133 results on '"Anita M. S. Richards"'
Search Results
2. Comment on 'Phosphine in the Venusian Atmosphere: A Strict Upper Limit from SOFIA GREAT Observations' by Cordiner et al
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Jane Greaves, Janusz Jurand Petkowski, Anita M S Richards, Clara Sousa-Silva, Sara Seager, and David L Clements
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Searches for phosphine in Venus’ atmosphere have sparked a debate. Cordiner et al. 2022 analyse spectra from the Stratospheric Observatory For Infrared Astronomy (SOFIA) and infer
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- 2023
3. Reply to: No evidence of phosphine in the atmosphere of Venus from independent analyses
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Clara Sousa-Silva, Anita M. S. Richards, Jane Greaves, Sukrit Ranjan, Paul B. Rimmer, Janusz J. Petkowski, Sara Seager, William Bains, David L. Clements, and Helen J. Fraser
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Atmosphere of Venus ,chemistry.chemical_compound ,chemistry ,Environmental science ,Astronomy and Astrophysics ,Phosphine ,Astrobiology - Published
- 2021
4. Addendum: Phosphine gas in the cloud deck of Venus
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E’lisa Lee, Anita M. S. Richards, Helen J. Fraser, Annabel Cartwright, Janusz J. Petkowski, Per Friberg, Jane Greaves, Clara Sousa-Silva, David L. Clements, Paul B. Rimmer, Ingo Mueller-Wodarg, Jim Hoge, Sara Seager, William Bains, Emily Drabek-Maunder, Sukrit Ranjan, Zhuchang Zhan, Iain Coulson, and Hideo Sagawa
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biology ,business.industry ,Addendum ,Astronomy and Astrophysics ,Venus ,Cloud computing ,biology.organism_classification ,Deck ,Astrobiology ,chemistry.chemical_compound ,chemistry ,Environmental science ,business ,Phosphine - Published
- 2021
5. (Sub)stellar companions shape the winds of evolved stars
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D. Gobrecht, Sandra Etoka, Malcolm Gray, I. El Mellah, Theo Khouri, W. Homan, K. T. Wong, Manali Jeste, Sofia Wallström, J. De Ridder, Pierre Kervella, E. De Beck, L. B. F. M. Waters, F. De Ceuster, E. Cannon, Leen Decin, E. Lagadec, Alain Baudry, Hugues Sana, Albert A. Zijlstra, Anita M. S. Richards, Taissa Danilovich, Raghvendra Sahai, J. A. Yates, J. Bolte, Carl A. Gottlieb, A. de Koter, John M. C. Plane, Karl M. Menten, M. Van de Sande, Iain McDonald, Miguel Montargès, Holger S. P. Müller, Tom J. Millar, Fabrice Herpin, Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), FEMIS 2021, Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), and Low Energy Astrophysics (API, FNWI)
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astro-ph.SR ,astro-ph.GA ,FOS: Physical sciences ,Binary number ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,01 natural sciences ,Submillimeter Array ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Asymptotic giant branch ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,ComputingMilieux_MISCELLANEOUS ,Astrophysics::Galaxy Astrophysics ,Physics ,Multidisciplinary ,010308 nuclear & particles physics ,Astrophysics - Astrophysics of Galaxies ,Planetary nebula ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,Astrophysics of Galaxies (astro-ph.GA) ,Physics::Space Physics ,Millimeter ,Astrophysics::Earth and Planetary Astrophysics ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] - Abstract
Binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. The evolution of a spherical wind from an asymptotic giant branch (AGB) star into a nonspherical planetary nebula (PN) could be due to binary interactions. We observed a sample of AGB stars with the Atacama Large Millimeter/submillimeter Array (ALMA) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (PNe). We infer that the same physics shapes both AGB winds and PNe; additionally, the morphology and AGB mass-loss rate are correlated. These characteristics can be explained by binary interaction. We propose an evolutionary scenario for AGB morphologies that is consistent with observed phenomena in AGB stars and PNe., 19 pages main journal, 97 pages Supplementary Information
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- 2020
6. Phosphine gas in the cloud decks of Venus
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Sara Seager, Jim Hoge, Janusz J. Petkowski, David L. Clements, Jane Greaves, E’lisa Lee, Paul B. Rimmer, Anita M. S. Richards, Per Friberg, Sukrit Ranjan, William Bains, Hideo Sagawa, Clara Sousa-Silva, Emily Drabek-Maunder, Zhuchang Zhan, Iain Coulson, Ingo Mueller-Wodarg, Helen J. Fraser, Annabel Cartwright, Greaves, JS [0000-0002-3133-413X], Richards, AMS [0000-0002-3880-2450], Rimmer, PB [0000-0002-7180-081X], Sagawa, H [0000-0003-2064-2863], Seager, S [0000-0002-6892-6948], Petkowski, JJ [0000-0002-1921-4848], Sousa-Silva, C [0000-0002-7853-6871], Mueller-Wodarg, I [0000-0001-6308-7826], Friberg, P [0000-0002-8010-8454], Apollo - University of Cambridge Repository, Science and Technology Facilities Council (STFC), Imperial College Trust, and Science and Technology Facilities Council
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010504 meteorology & atmospheric sciences ,sub-01 ,FOS: Physical sciences ,SULFUR ,Venus ,Cloud computing ,5109 Space Sciences ,Astronomy & Astrophysics ,01 natural sciences ,Astrobiology ,Atmosphere ,chemistry.chemical_compound ,CHEMISTRY ,0103 physical sciences ,LOWER ATMOSPHERE ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Earth and Planetary Astrophysics (astro-ph.EP) ,SPECTRUM ,geography ,Science & Technology ,geography.geographical_feature_category ,biology ,sub-99 ,business.industry ,Nearest neighbour ,Astronomy and Astrophysics ,biology.organism_classification ,Lightning ,Trace gas ,LIFE ,Volcano ,chemistry ,WATER-VAPOR ,5101 Astronomical Sciences ,13. Climate action ,Physical Sciences ,PH3 ,ENCELADUS ,CHEMICAL KINETIC-MODEL ,business ,51 Physical Sciences ,5107 Particle and High Energy Physics ,Phosphine ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Measurements of trace gases in planetary atmospheres help us explore chemical conditions different to those on Earth. Our nearest neighbour, Venus, has cloud decks that are temperate but hyperacidic. Here we report the apparent presence of phosphine (PH3) gas in Venus’s atmosphere, where any phosphorus should be in oxidized forms. Single-line millimetre-waveband spectral detections (quality up to ~15σ) from the JCMT and ALMA telescopes have no other plausible identification. Atmospheric PH3 at ~20 ppb abundance is inferred. The presence of PH3 is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venus’s atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery. PH3 could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of PH3 on Earth, from the presence of life. Other PH3 spectral features should be sought, while in situ cloud and surface sampling could examine sources of this gas. The detection of ~20 ppb of phosphine in Venus clouds by observations in the millimetre-wavelength range from JCMT and ALMA is puzzling, because according to our knowledge of Venus, no phosphine should be there. As the most plausible formation paths do not work, the source could be unknown chemical processes—maybe even life?
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- 2020
7. Venusian phosphine: a 'Wow!' signal in chemistry?
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Sukrit Ranjan, Clara Sousa-Silva, William Bains, Zhuchang Zhan, Paul B. Rimmer, Jane S. Greaves, Anita M. S. Richards, Sara Seager, and Janusz J. Petkowski
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Earth and Planetary Astrophysics (astro-ph.EP) ,biology ,Organic Chemistry ,FOS: Physical sciences ,Biosphere ,Venus ,biology.organism_classification ,Biochemistry ,Astrobiology ,Inorganic Chemistry ,Atmosphere ,Scientific debate ,Consensus model ,Astrophysics - Instrumentation and Methods for Astrophysics ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,Astrophysics - Earth and Planetary Astrophysics - Abstract
The potential detection of ppb levels phosphine (PH3) in the clouds of Venus through millimeter-wavelength astronomical observations is extremely surprising as PH3 is an unexpected component of an oxidized environment of Venus. A thorough analysis of potential sources suggests that no known process in the consensus model of Venus' atmosphere or geology could produce PH3 at anywhere near the observed abundance. Therefore, if the presence of PH3 in Venus' atmosphere is confirmed, it is highly likely to be the result of a process not previously considered plausible for Venusian conditions. The source of atmospheric PH3 could be unknown geo- or photochemistry, which would imply that the consensus on Venus' chemistry is significantly incomplete. An even more extreme possibility is that strictly aerial microbial biosphere produces PH3. This paper summarizes the Venusian PH3 discovery and the scientific debate that arose since the original candidate detection one year ago., A short overview of the Venusian PH3 discovery and the scientific debate that arose since the original candidate detection in September 2020. Additional discussion of possible non-canonical sources of PH3 on Venus is also included. arXiv admin note: text overlap with arXiv:2009.06499
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- 2021
8. ATOMIUM: The astounding complexity of the near circumstellar environment of the M-type AGB star R Hydrae - I. Morpho-kinematical interpretation of CO and SiO emission
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John M. C. Plane, Raghvendra Sahai, Dylan Kee, Tom J. Millar, Fabrice Herpin, Alain Baudry, Joe Nuth, Ward Homan, Iain McDonald, S. Maes, Albert A. Zijlstra, Malcolm Gray, Marie Van de Sande, D. Gobrecht, K. T. Wong, Holger S. P. Müller, Alex de Koter, Bannawit Pimpanuwat, Taissa Danilovich, Eric Lagadec, Jan Philip Sindel, Frederik De Ceuster, Kelvin Lee, Sofia Wallström, Anita M. S. Richards, J. Malfait, Miguel Montargès, Sandra Etoka, Jeremy Yates, Leen Decin, Carl A. Gottlieb, Rens Waters, Pierre Kervella, J. Bolte, Ileyk El Mellah, E. Cannon, Daniel Price, Manali Jeste, Karl M. Menten, and Low Energy Astrophysics (API, FNWI)
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Shock wave ,media_common.quotation_subject ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Submillimeter Array ,Physics::Fluid Dynamics ,0103 physical sciences ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,Angular resolution ,010306 general physics ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,media_common ,Physics ,Nebula ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy and Astrophysics ,Position angle ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,Sky ,Astrophysics::Earth and Planetary Astrophysics - Abstract
Evolved low- to intermediate-mass stars are known to shed their gaseous envelope into a large, dusty, molecule-rich circumstellar nebula which typically develops a high degree of structural complexity. Most of the large-scale, spatially correlated structures in the nebula are thought to originate from the interaction of the stellar wind with a companion. As part of the Atomium large programme, we observed the M-type asymptotic giant branch (AGB) star R Hydrae with ALMA. The morphology of the inner wind of R Hya, which has a known companion at ~3500 au, was determined from maps of CO and SiO obtained at high angular resolution. A map of the CO emission reveals a multi-layered structure consisting of a large elliptical feature at an angular scale of ~10'' that is oriented along the north-south axis. The wind morphology within the elliptical feature is dominated by two hollow bubbles. The bubbles are on opposite sides of the AGB star and lie along an axis with a position angle of ~115 deg. Both bubbles are offset from the central star, and their appearance in the SiO channel maps indicates that they might be shock waves travelling through the AGB wind. An estimate of the dynamical age of the bubbles yields an age of the order of 100 yr, which is in agreement with the previously proposed elapsed time since the star last underwent a thermal pulse. When the CO and SiO emission is examined on subarcsecond angular scales, there is evidence for an inclined, differentially rotating equatorial density enhancement, strongly suggesting the presence of a second nearby companion. The position angle of the major axis of this disc is ~70 deg in the plane of the sky. We tentatively estimate that a lower limit on the mass of the nearby companion is ~0.65 Msol on the basis of the highest measured speeds in the disc and the location of its inner rim at ~6 au from the AGB star., 21 pages, 23 figures
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- 2021
9. ATOMIUM: A high-resolution view on the highly asymmetric wind of the AGB star pi(1)Gruis: I. First detection of a new companion and its effect on the inner wind
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Marie Van de Sande, Eric Lagadec, Dylan Kee, Raghvendra Sahai, Holger S. P. Müller, Alain Baudry, Albert A. Zijlstra, Joe Nuth, D. Gobrecht, Malcolm D. Grey, Tom J. Millar, Ileyk El Mellah, Alex de Koter, Kelvin Lee, Elaine Gottlieb, Iain McDonald, E. Cannon, Bannawit Pimpanuwat, M. Montargès, K. T. Wong, Manali Jeste, Karl M. Menten, Fabrice Herpin, Jeremy Yates, Ward Homan, Jan Philip Sindel, Frederik De Ceuster, Anita M. S. Richards, Sandra Etoka, Taissa Danilovich, Sofia Wallström, J. Bolte, John M. C. Plane, Daniel J. Price, Leen Decin, Carl A. Gottlieb, Pierre Kervella, Rens Waters, and Low Energy Astrophysics (API, FNWI)
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CIRCUMSTELLAR ENVELOPES ,Astrophysics::High Energy Astrophysical Phenomena ,Continuum (design consultancy) ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,PLANETARY-NEBULA ,Astronomy & Astrophysics ,01 natural sciences ,Submillimeter Array ,Computer Science::Digital Libraries ,circumstellar matter ,law.invention ,law ,DUSTY WINDS ,0103 physical sciences ,profiles [line] ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,Maser ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,BIPOLAR PREPLANETARY NEBULAE ,Physics ,Spiral galaxy ,Science & Technology ,stars [submillimeter] ,010308 nuclear & particles physics ,S-STARS ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy and Astrophysics ,MASS-LOSS ,AGB and post-AGB [stars] ,Physics::History of Physics ,ELECTRIC-DIPOLE ,BINARY-SYSTEMS ,RED GIANTS ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,SIO ,Physical Sciences ,Millimeter ,Astrophysics::Earth and Planetary Astrophysics ,Spiral (railway) - Abstract
The nebular circumstellar environments of cool evolved stars are known to harbour a rich morphological complexity of gaseous structures on different length scales. A large part of these density structures are thought to be brought about by the interaction of the stellar wind with a close companion. The S-type asymptotic giant branch star Pi1 Gruis, which has a known companion at ~440 au and is thought to harbour a second, closer-by (, 19 pages, 20 figures
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- 2020
10. A detailed view on the circumstellar environment of the M-type AGB star EP Aquarii I. High-resolution ALMA and SPHERE observations
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Miguel Montargès, Anita M. S. Richards, Ward Homan, E. Cannon, Leen Decin, Tom J. Millar, Cannon, Emily, Montarges, Miguel, Richards, Anita MS, Millar, Tom J, and Decin, Leen
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Brightness ,FOS: Physical sciences ,High resolution ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,01 natural sciences ,Computer Science::Digital Libraries ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Asymptotic giant branch ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,Physics ,010308 nuclear & particles physics ,Photodissociation ,Astrophysics::Instrumentation and Methods for Astrophysics ,White dwarf ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Physics::History of Physics ,Interstellar medium ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,Astrophysics of Galaxies (astro-ph.GA) ,Outflow ,Astrophysics::Earth and Planetary Astrophysics - Abstract
Cool evolved stars are known to be significant contributors to the enrichment of the interstellar medium through their dense and dusty stellar winds. High resolution observations of these outflows have shown them to possess high degrees of morphological complexity. We observed the asymptotic giant branch (AGB) star EP Aquarii with ALMA in band 6 and VLT/SPHERE/ZIMPOL in four filters the visible. Both instruments had an angular resolution of 0.025''. These are follow-up observations to the lower-resolution 2016 ALMA analysis of EP Aquarii, which revealed that its wind possesses a nearly face-on, spiral-harbouring equatorial density enhancement, with a nearly pole-on bi-conical outflow. At the base of the spiral, the SiO emission revealed a distinct emission void approximately 0.4'' to the west of the continuum brightness peak, which was proposed to be linked to the presence of a companion. The new ALMA data better resolve the inner wind and reveal that its morphology as observed in CO is consistent with hydrodynamical companion-induced perturbations. Assuming that photodissociation by the UV-field of the companion is responsible for the emission void in SiO, we deduced the spectral properties of the tentative companion from the size of the hole. We conclude that the most probable companion candidate is a white dwarf with a mass between 0.65 and 0.8 Msol , though a solar-like companion could not be definitively excluded. The radial SiO emission shows periodic, low-amplitude perturbations. We tentatively propose that they could be the consequence of the interaction of the AGB wind with another much closer low-mass companion. The polarised SPHERE/ZIMPOL data show a circular signal surrounding the AGB star with a radius of 0.1''..., 24 pages, 25 Figures
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- 2020
11. Phosphine on Venus Cannot be Explained by Conventional Processes
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Sukrit Ranjan, Sara Seager, Anita M. S. Richards, Clara Sousa-Silva, Zhuchang Zhan, Janusz J. Petkowski, Jane Greaves, Paul B. Rimmer, and William Bains
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Haze ,Extraterrestrial Environment ,Phosphines ,FOS: Physical sciences ,Venus ,Astrobiology ,Atmosphere of Venus ,Atmosphere ,chemistry.chemical_compound ,Planet ,Physics - Chemical Physics ,Biosignature ,Earth and Planetary Astrophysics (astro-ph.EP) ,Chemical Physics (physics.chem-ph) ,biology ,Other Quantitative Biology (q-bio.OT) ,biology.organism_classification ,Agricultural and Biological Sciences (miscellaneous) ,Quantitative Biology - Other Quantitative Biology ,chemistry ,Space and Planetary Science ,FOS: Biological sciences ,Environmental science ,Phosphine ,Astrophysics - Earth and Planetary Astrophysics - Abstract
The recent candidate detection of ~1 ppb of phosphine in the middle atmosphere of Venus is so unexpected that it requires an exhaustive search for explanations of its origin. Phosphorus-containing species have not been modelled for Venus' atmosphere before and our work represents the first attempt to model phosphorus species in the Venusian atmosphere. We thoroughly explore the potential pathways of formation of phosphine in a Venusian environment, including in the planet's atmosphere, cloud and haze layers, surface, and subsurface. We investigate gas reactions, geochemical reactions, photochemistry, and other non-equilibrium processes. None of these potential phosphine production pathways are sufficient to explain the presence of ppb phosphine levels on Venus. If PH3's presence in Venus' atmosphere is confirmed, it therefore is highly likely to be the result of a process not previously considered plausible for Venusian conditions. The process could be unknown geochemistry, photochemistry, or even aerial microbial life, given that on Earth phosphine is exclusively associated with anthropogenic and biological sources. The detection of phosphine adds to the complexity of chemical processes in the Venusian environment and motivates in situ follow up sampling missions to Venus. Our analysis provides a template for investigation of phosphine as a biosignature on other worlds., v2 is in press in Astrobiology, Special Collection: Venus; v2 also expands on the potential of phosphides from the deep mantle volcanism as a source of PH3 (as suggested by Truong and Lunine 2021: https://www.pnas.org/content/118/29/e2021689118) and shows the volcanic source of PH3 to be unlikely
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- 2020
12. Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse
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Edward F. Guinan, Anita M. S. Richards, Richard Wasatonic, Lynn D. Matthews, Michael Weber, Miguel Montargès, Reimar Leike, Thomas Calderwood, Andrea K. Dupree, Han Uitenbroek, Klaus G. Strassmeier, and Thomas Granzer
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010504 meteorology & atmospheric sciences ,IMAGES ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astrophysics ,Astronomy & Astrophysics ,LONG SECONDARY PERIODS ,01 natural sciences ,Stellar mass loss ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Stellar chromospheres ,010303 astronomy & astrophysics ,Chromosphere ,Solar and Stellar Astrophysics (astro-ph.SR) ,Space Telescope Imaging Spectrograph ,Physics::Atmospheric and Oceanic Physics ,Astrophysics::Galaxy Astrophysics ,0105 earth and related environmental sciences ,Line (formation) ,Betelgeuse ,Physics ,M supergiant stars ,Photosphere ,Science & Technology ,CHROMOSPHERE ,Stellar atmosphere ,Astronomy and Astrophysics ,Stellar atmospheres ,ALPHA ,VARIABILITY ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,Physical Sciences ,LUMINOSITY ,Astrophysics::Earth and Planetary Astrophysics ,Supergiant - Abstract
The bright supergiant, Betelgeuse (Alpha Orionis, HD 39801) experienced a visual dimming during 2019 December and the first quarter of 2020 reaching an historic minimum 2020 February 7$-$13. During 2019 September-November, prior to the optical dimming event, the photosphere was expanding. At the same time, spatially resolved ultraviolet spectra using the Hubble Space Telescope/Space Telescope Imaging Spectrograph revealed a substantial increase in the ultraviolet spectrum and Mg II line emission from the chromosphere over the southern hemisphere of the star. Moreover, the temperature and electron density inferred from the spectrum and C II diagnostics also increased in this hemisphere. These changes happened prior to the Great Dimming Event. Variations in the Mg II k-line profiles suggest material moved outwards in response to the passage of a pulse or acoustic shock from 2019 September through 2019 November. It appears that this extraordinary outflow of material from the star, likely initiated by convective photospheric elements, was enhanced by the coincidence with the outward motions in this phase of the $\sim$400 day pulsation cycle. These ultraviolet observations appear to provide the connecting link between the known large convective cells in the photosphere and the mass ejection event that cooled to form the dust cloud in the southern hemisphere imaged in 2019 December, and led to the exceptional optical dimming of Betelgeuse in 2020 February., 11 pages, 8 figures, Astrophysical Journal, accepted
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- 2020
13. COBRaS: the e-MERLIN 21 cm Legacy survey of Cygnus OB2
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Nicholas J. Wright, Sean M. Dougherty, J. S. Clark, Jeremy Yates, R. K. Prinja, H. A. Smith, Danielle Fenech, Jorick S. Vink, Anita M. S. Richards, Jeremy J. Drake, Julian M. Pittard, Ian R. Stevens, Ronny Blomme, S. P. S. Eyres, and J. C. Morford
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Hubble Deep Field ,Young stellar object ,Binary number ,FOS: Physical sciences ,Astrophysics ,F500 ,01 natural sciences ,0103 physical sciences ,massive [Stars] ,Radiative transfer ,winds, outflows [Stars] ,open clusters and associations: individual: Cygnus OB2 ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Physics ,stars: winds, outflows ,010308 nuclear & particles physics ,Star formation ,Astronomy and Astrophysics ,Astrophysics - Astrophysics of Galaxies ,individual: Cygnus OB2 [Open clusters and associations] ,Galaxy ,stars: massive ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,techniques: interferometric ,Astrophysics of Galaxies (astro-ph.GA) ,interferometric [Techniques] ,stars [Radio continuum] ,Cygnus OB2 ,radio continuum: stars ,QB799 - Abstract
The role of massive stars is central to an understanding of galactic ecology. It is important to establish the details of how massive stars provide radiative, chemical, and mechanical feedback in galaxies. Central to these issues is an understanding of the evolution of massive stars, and the critical role of mass loss via strongly structured winds and stellar binarity. Ultimately, massive stellar clusters shape the structure and energetics of galaxies. We aim to conduct high-resolution, deep field mapping at 21cm of the core of the massive Cygnus OB2 association and to characterise the properties of the massive stars and colliding winds at this waveband. We used seven stations of the e-MERLIN radio facility, with its upgraded bandwidth and enhanced sensitivity to conduct a 21cm census of Cygnus OB2. Based on 42 hours of observations, seven overlapping pointings were employed over multiple epochs during 2014 resulting in 1 sigma sensitivities down to ~21microJy and a resolution of ~180mas. A total of 61 sources are detected at 21cm over a ~0.48deg x 0.48deg region centred on the heart of the Cyg OB2 association. Of these 61 sources, 33 are detected for the first time. We detect a number of previously identified sources including four massive stellar binary systems, two YSOs, and several known X-ray and radio sources. We also detect the LBV candidate (possible binary system) and blue hypergiant (BHG) star of Cyg OB2 #12. The 21cm observations secured in the COBRaS Legacy project provide data to constrain conditions in the outer wind regions of massive stars; determine the non-thermal properties of massive interacting binaries; examine evidence for transient sources, including those associated with young stellar objects; and provide unidentified sources that merit follow-up observations. The 21cm data are of lasting value and will serve in combination with other key surveys of Cyg OB2., 41 pages, 12 figures, accepted in A&A
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- 2020
14. ALMA High-frequency Long Baseline Campaign in 2017: Band-to-band Phase Referencing in Submillimeter Waves
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Tsuyoshi Sawada, Akihiko Hirota, Satoko Takahashi, Neil M. Phillips, Eric Villard, John M. Carpenter, Luke T. Maud, Anita M. S. Richards, Elizabeth M. Humphreys, Yoshiharu Asaki, William R. F. Dent, Edward B. Fomalont, Stuartt Corder, and L. Barcos-Muñoz
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Physics ,Differential gain ,business.industry ,Image quality ,Phase (waves) ,FOS: Physical sciences ,Astronomy and Astrophysics ,01 natural sciences ,Submillimeter Array ,010309 optics ,Wavelength ,Optics ,Space and Planetary Science ,0103 physical sciences ,Calibration ,Angular resolution ,Millimeter ,business ,Astrophysics - Instrumentation and Methods for Astrophysics ,010303 astronomy & astrophysics ,Instrumentation and Methods for Astrophysics (astro-ph.IM) - Abstract
In 2017, an Atacama Large Millimeter/submillimeter Array (ALMA) high-frequency long baseline campaign was organized to test image capabilities with baselines up to 16 km at submillimeter (submm) wavelengths. We investigated image qualities using ALMA receiver Bands 7, 8, 9, and 10 (285-875 GHz) by adopting band-to-band (B2B) phase referencing in which a phase calibrator is tracked at a lower frequency. For B2B phase referencing, it is expected that a closer phase calibrator to a target can be used, comparing to standard in-band phase referencing. In the first step, it is ensured that an instrumental phase offset difference between low- and high-frequency Bands can be removed using a differential gain calibration in which a phase calibrator is certainly detected while frequency switching. In the next step, comparative experiments are arranged to investigate the image quality between B2B and in-band phase referencing with phase calibrators at various separation angles. In the final step, we conducted long baseline imaging tests for a quasar at 289 GHz in Band 7 and 405 GHz in Band 8 and complex structure sources of HL Tau and VY CMa at ~670 GHz in Band 9. The B2B phase referencing was successfully applied, allowing us to achieve an angular resolution of 14x11 and 10x8 mas for HL Tau and VY CMa, respectively. There is a high probability of finding a low-frequency calibrator within 5.4 deg in B2B phase referencing, bright enough to use an 8 s scan length combined with a 7.5 GHz bandwidth., Comment: 61 pages, 17 figures, 8 tables
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- 2020
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15. Circumstellar CO J = 3-2 detected around the evolving metal-poor ([Fe/H] ~ -1.15 dex) AGB star RU Vulpeculae
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Anita M. S. Richards, S. Uttenthaler, Iain McDonald, Eric Lagadec, and Albert A. Zijlstra
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Physics ,Infrared excess ,010308 nuclear & particles physics ,Infrared ,FOS: Physical sciences ,Flux ,Astronomy and Astrophysics ,Astrophysics ,01 natural sciences ,Silicate ,Stars ,chemistry.chemical_compound ,chemistry ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,0103 physical sciences ,Asymptotic giant branch ,Absorption (electromagnetic radiation) ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Line (formation) - Abstract
We report the first detection of CO J = 3-2 around a truly metal-poor evolved star. RU Vulpeculae is modelled to have Teff ~ 3620 K, L ~ 3128 +/- 516 L_Sun, log(g) = 0.0 ~ 0.2 dex and [Fe/H] = -1.3 to -1.0 dex, and is modelled to have recently undergone a thermal pulse. Its infrared flux has approximately doubled over 35 years. ALMA observations show the 3-2 line is narrow (half-width ~1.8-3.5 km/s). The 2-1 line is much weaker: it is not confidently detected. Spectral-energy-distribution fitting indicates very little circumstellar absorption, despite its substantial mid-infrared emission. A VISIR mid-infrared spectrum shows features typical of previously observed metal-poor stars, dominated by a substantial infrared excess but with weak silicate and (possibly) Al2O3 emission. A lack of resolved emission, combined with weak 2!1 emission, indicates the dense circumstellar material is truncated at large radii. We suggest that rapid dust condensation is occurring, but with an aspherical geometry (e.g., a disc or clumps) that does not obscure the star. We compare with T UMi, a similar star which is currently losing its dust., Accepted MNRAS, 16 pages, 7 figures
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- 2019
16. SOFIA upGREAT/FIFI-LS Emission-line Observations of Betelgeuse during the Great Dimming of 2019/2020
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Anita M. S. Richards, Richard Wasatonic, Nils Ryde, Christian Fischer, Urs U. Graf, Helmut Wiesemeyer, Edward F. Guinan, Graham M. Harper, Dario Fadda, William D. Vacca, Sebastian Colditz, Robert F. Minchin, Edward T. Chambers, Matthew J. Richter, and Curtis DeWitt
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Physics ,Betelgeuse ,Space and Planetary Science ,Astronomy ,Astronomy and Astrophysics ,Emission spectrum - Abstract
We report NASA-DLR SOFIA upGREAT circumstellar [O i] 63.2 μm and [C ii] 157.7 μm emission profiles and FIFI-LS [O i] 63.2 μm, [O i] 145.5 μm, and [C ii] 157.7 μm fluxes obtained shortly after Betelgeuse’s 2019/2020 Great Dimming event. Haas et al. noted a potential correlation between the [O i] 63.2 μm flux and V magnitude based on three Kuiper Airborne Observatory observations made with the CGS and FIFI instruments. The FIFI observation was obtained when V ≃ 0.88 and revealed a 3σ non-detection at a quarter of the previous CGS flux measurement made when V ≃ 0.35. A potential explanation could be a change in dust-gas drag heating by circumstellar silicates caused by variations in the photospheric radiation field. SOFIA observations provide a unique test of this correlation because the V-band brightness went to its lowest value on record, V ≃ 1.61, with the SOFIA observations being made when V FIFI−LS ≃ 1.51 and V upGREAT ≃ 1.36. The upGREAT spectra show a [O i] 63.2 μm flux larger than previous space observatory measurements obtained when V ≃ 0.58. The profile is consistent with formation in the slower, more turbulent inner S1 outflow, while the [C ii] 157.7 μm profile is consistent with formation farther out in the faster S2 outflow. Modeling of dust-gas drag heating, combined with 25 yr of Wing three-filter and V photometry, reveals that it is unlikely that the S1 circumstellar envelope and [O i] 63.2 μm fluxes are dominated by the dust-gas drag heating and that another heating source is also active. The [O i] 63.2 μm profile is hard to reconcile with existing outflow velocity models.
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- 2021
17. Detailed SiO proper motion analysis: slow net expansion and a small correlation with the magnetic field
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Bill Cotton, K. Assaf, P. J. Diamond, Liz Humphreys, Anita M. S. Richards, Malcolm Gray, Markus Wittkowski, and Sandra Etoka
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Physics ,Brightness ,Photosphere ,Proper motion ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Polarization (waves) ,Kinetic energy ,law.invention ,Magnetic field ,Stars ,law ,Astrophysics::Solar and Stellar Astrophysics ,Maser ,Astrophysics::Galaxy Astrophysics - Abstract
A detailed analysis of 23 epochs (covering two stellar cycles) of monitoring R Cas SiO J=1-0 v=1 masers showed 184 maser features (an average of 20% per epoch) could be matched over between 3 and 13 epochs. The largest number of matches occur in the early part of each cycle, following the maser brightness trends, which are roughly as predicted. The proper motions can be tangential, radial, intermediate or change direction, but overall the net direction is expansion corresponding to ~0.4(0.1) km/s. This would take ~67 year to cross the SiO maser shell, giving a mass loss rate similar to other estimates in the literature. A small proportion of feature pairs in successive epochs have significant polarization and polarization angles consistent to within pi/8 rad. A small excess of this subsample have proper motion vectors within 22.5 deg of parallel to the inferred magnetic field direction (2sigma significance) but this is in radial expansion for less than half of these. The magnetic field strength provides a force comparable to the kinetic and thermal energy densities and could influence their directions, but it does not appear to be driving the majority of motions of gas clumps. The SiO masers typically emanate from a shell within 2-5 optical stellar radii, which is also the region where the radio photosphere becomes optically thick at 1.3 - 6 cm wavelength, and where molecular or dust emission can be traced by IR interferometry. Recent advances in techniques and e-MERLIN K-band observations will allow improved coordination between maser and continuum/IR observations in the investigation of how exactly mass is lost from stars.
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- 2019
18. Circumstellar CO in metal-poor stellar winds: the highly irradiated globular cluster star 47 Tucanae V3
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Iain McDonald, Eric Lagadec, Albert A. Zijlstra, Gregory C. Sloan, Anita M. S. Richards, Martha L. Boyer, and Martin Groenewegen
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Opacity ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,circumstellar matter ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,individual: NGC 104 [globular clusters] ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,Maser ,winds, outflows [stars] ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Physics ,Photosphere ,stars [infrared] ,010308 nuclear & particles physics ,mass-loss [stars] ,Astronomy and Astrophysics ,AGB and post-AGB [stars] ,Astrophysics - Astrophysics of Galaxies ,Grain size ,Stars ,Radiation pressure ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,Globular cluster ,Astrophysics of Galaxies (astro-ph.GA) ,Astrophysics::Earth and Planetary Astrophysics - Abstract
We report the first detection of circumstellar CO in a globular cluster. Observations with ALMA have detected the CO J=3-2 and SiO v=1 J=8-7 transitions at 345 and 344 GHz, respectively, around V3 in 47 Tucanae (NGC 104; [Fe/H] = -0.72 dex), a star on the asymptotic giant branch. The CO line is detected at 7 sigma at a rest velocity v_LSR = -40.6 km/s and expansion velocity of 3.2 +/- ~0.4 km/s. The brighter, asymmetric SiO line may indicate a circumstellar maser. The stellar wind is slow compared to similar Galactic stars, but the dust opacity remains similar to Galactic comparisons. We suggest that the mass-loss rate is set by the levitation of material into the circumstellar environment by pulsations, but that the terminal wind-expansion velocity is determined by radiation pressure on the dust: a pulsation-enhanced dust-driven wind. We suggest the metal-poor nature of the star decreases the grain size, slowing the wind and increasing its density and opacity. Metallic alloys at high altitudes above the photosphere could also provide an opacity increase. The CO line is weaker than expected from Galactic AGB stars, but its strength confirms a model that includes CO dissociation by the strong interstellar radiation field present inside globular clusters., Comment: 5 pages, accepted MNRAS Letters
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- 2019
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19. An unusual face-on spiral in the wind of the M-type AGB star EP Aquarii (Corrigendum)
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Alex de Koter, Anita M. S. Richards, Leen Decin, Ward Homan, Pierre Kervella, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
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[PHYS]Physics [physics] ,Physics ,010308 nuclear & particles physics ,Astronomy and Astrophysics ,Astrophysics ,Type (model theory) ,01 natural sciences ,[SDU]Sciences of the Universe [physics] ,Space and Planetary Science ,0103 physical sciences ,Radiative transfer ,Asymptotic giant branch ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,010303 astronomy & astrophysics ,ComputingMilieux_MISCELLANEOUS ,Unusual face ,Spiral - Abstract
International audience
- Published
- 2019
20. An unusual face-on spiral in the wind of the M-type AGB star EP Aquarii
- Author
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Pierre Kervella, Anita M. S. Richards, Ward Homan, Alex de Koter, Leen Decin, Institute of Astronomy [Leuven], Catholic University of Leuven - Katholieke Universiteit Leuven (KU Leuven), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Low Energy Astrophysics (API, FNWI), and PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Brightness ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Spectral line ,0103 physical sciences ,Radiative transfer ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,010306 general physics ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,ComputingMilieux_MISCELLANEOUS ,Physics ,[PHYS]Physics [physics] ,Astronomy and Astrophysics ,Position angle ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,Substructure ,Outflow ,Astrophysics::Earth and Planetary Astrophysics ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] - Abstract
High-resolution interferometric observations of the circumstellar environments of AGB stars show a variety of morphologies. Guided by the unusual carbon monoxide line profile of the AGB star EP Aquarii, we have observed its circumstellar environment with ALMA band 6 in cycle 4. We describe the morphological complexity of the CO, SiO and SO2 molecular emission. The CO emission exhibits the characteristics of a bi-conical wind with a bright nearly face-on spiral feature around the systemic velocity. This is the first convincing detection of a spiral morphology in an O-rich wind. Based on the offsets of the centers of the two bi-conical wind hemispheres, we deduce the position angle of the inclination axis to be ~150 deg measured counterclockwise from north. Based on the velocity width of the spiral signature we estimate the inclination angle of the system to be between 4 deg and 18 deg. The central emission zone exhibits a morphology that resembles simulations modelling the spiral-inducing wind-Roche-lobe-overflow mechanism. Though the spiral may be a (companion-induced) density enhancement in the stellar outflow, the extremely narrow width of the spiral signature in velocity space suggests that it may be a hydrodynamical perturbation in a face-on differentially rotating disk. The SiO emission does not show the spiral, but exhibits a local emission void approximately 0.5'' west of the continuum brightness peak. We hypothesise that this may be a local environment caused by the presence of a (stellar) companion with a mass of at most 0.1 Msol, based on its non-detection in the continuum..., 20 pages, 16 Figures
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- 2018
21. High Angular Resolution ALMA Images of Dust and Molecules in the SN 1987A Ejecta
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Jason Spyromilio, Sangwook Park, Giovanna Zanardo, Bryan Gaensler, Patrick F. Roche, M. J. Barlow, Jacco Th. van Loon, Remy Indebetouw, Anita M. S. Richards, J. C. Wheeler, Phil Cigan, Hans-Thomas Janka, Patrice Bouchet, J. M. Marcaide, Timothy A. Davis, Cherry Ng, David N. Burrows, Haley Louise Gomez, Dennis Alp, Josefin Larsson, F. J. Abellan, Mikako Matsuura, Eli Dwek, Claes Fransson, Michael Gabler, Peter Lundqvist, Département d'Astrophysique (ex SAP) (DAP), Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), and Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112))
- Subjects
astro-ph.SR ,010504 meteorology & atmospheric sciences ,FOS: Physical sciences ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,01 natural sciences ,Spectral line ,Nucleosynthesis ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Molecule ,Ejecta ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics ,0105 earth and related environmental sciences ,astro-ph.HE ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,Astronomy and Astrophysics ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Spectral energy distribution ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics - High Energy Astrophysical Phenomena ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,QB799 - Abstract
We present high angular resolution (~80 mas) ALMA continuum images of the SN 1987A system, together with CO $J$=2 $\!\rightarrow\!$ 1, $J$=6 $\!\rightarrow\!$ 5, and SiO $J$=5 $\!\rightarrow\!$ 4 to $J$=7 $\!\rightarrow\!$ 6 images, which clearly resolve the ejecta (dust continuum and molecules) and ring (synchrotron continuum) components. Dust in the ejecta is asymmetric and clumpy, and overall the dust fills the spatial void seen in H$\alpha$ images, filling that region with material from heavier elements. The dust clumps generally fill the space where CO $J$=6 $\!\rightarrow\!$ 5 is fainter, tentatively indicating that these dust clumps and CO are locationally and chemically linked. In these regions, carbonaceous dust grains might have formed after dissociation of CO. The dust grains would have cooled by radiation, and subsequent collisions of grains with gas would also cool the gas, suppressing the CO $J$=6 $\!\rightarrow\!$ 5 intensity. The data show a dust peak spatially coincident with the molecular hole seen in previous ALMA CO $J$=2 $\!\rightarrow\!$ 1 and SiO $J$=5 $\!\rightarrow\!$ 4 images. That dust peak, combined with CO and SiO line spectra, suggests that the dust and gas could be at higher temperatures than the surrounding material, though higher density cannot be totally excluded. One of the possibilities is that a compact source provides additional heat at that location. Fits to the far-infrared--millimeter spectral energy distribution give ejecta dust temperatures of 18--23K. We revise the ejecta dust mass to $\mathrm{M_{dust}} = 0.2-0.4$M$_\odot$ for carbon or silicate grains, or a maximum of $, Comment: 32 pages, containing 19 figures and three appendices
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- 2019
22. ALMA observations of the nearby AGB star L$_{\rm 2}$ Puppis. II. Gas disk properties derived from $^{\rm 12}$CO and $^{\rm13}$CO $J=$3$-$2 emission
- Author
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Leen Decin, Anita M. S. Richards, Iain McDonald, Alex de Koter, Pierre Kervella, Ward Homan, K. Ohnaka, and Low Energy Astrophysics (API, FNWI)
- Subjects
Physics ,molecular data ,010308 nuclear & particles physics ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,stars / stars ,AGB and post-AGB ,circumstellar matter ,7. Clean energy ,01 natural sciences ,3. Good health ,Astrophysics - Solar and Stellar Astrophysics ,radiative transfer ,Space and Planetary Science ,0103 physical sciences ,Radiative transfer ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,submillimeter ,Astrophysics::Earth and Planetary Astrophysics ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics - Abstract
The circumstellar environment of the AGB star L$_{\rm 2}$ Puppis was observed with ALMA in cycle 3, with a resolution of $15 \times 18 \rm\ mas$. The molecular emission shows a differentially rotating disk, inclined to a nearly edge-on position. In the first paper in this series (paper I) the molecular emission was analysed to accurately deduce the motion of the gas in the equatorial regions of the disk. In this work we model the optically thick $^{\rm 12}$CO $J=$3$-$2 and the optically thin $^{\rm 13}$CO $J=$3$-$2 rotational transition to constrain the physical conditions in the disk. To realise this effort we make use of the 3D NLTE radiative transfer code {\tt LIME}. The temperature structure and velocity structure show a high degree of complexity, both radially and vertically. The radial H$_{\rm 2}$ density profile in the disk plane is characterised by a power law with a slope of $-3.1$. We find a $^{\rm 12}$CO over $^{\rm 13}$CO abundance ratio of 10 inside the disk. Finally, estimations of the angular momentum in the disk surpass the expected available angular momentum of the star, strongly supporting the indirect detection of a compact binary companion reported in paper I. We estimate the mass of the companion to be around 1 Jupiter mass., 21 pages; 19 figures
- Published
- 2018
23. Methanol masers and magnetic field in IRAS18089-1732
- Author
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Henrik Beuther, Wouter Vlemmings, Daria Dall'Olio, G. Surcis, Anita M. S. Richards, E. Varenius, Boy Lankhaar, M. V. Persson, ITA, GBR, DEU, and SWE
- Subjects
Field (physics) ,Star formation ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Polarization (waves) ,Accretion (astrophysics) ,Magnetic field ,law.invention ,Space and Planetary Science ,law ,Bipolar outflow ,Protostar ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Maser ,Astrophysics::Galaxy Astrophysics - Abstract
Theoretical simulations have shown that magnetic fields play an important role in massive star formation: they can suppress fragmentation in the star forming cloud, enhance accretion via disc and regulate outflows and jets. However, models require specific magnetic configurations and need more observational constraints to properly test the impact of magnetic fields. We investigate the magnetic field structure of the massive protostar IRAS18089-1732, analysing 6.7 GHz CH3OH maser MERLIN observations. IRAS18089-1732 is a well studied high mass protostar, showing a hot core chemistry, an accretion disc and a bipolar outflow. An ordered magnetic field oriented around its disc has been detected from previous observations of polarised dust. This gives us the chance to investigate how the magnetic field at the small scale probed by masers relates to the large scale field probed by the dust.
- Published
- 2018
24. The 6-GHz multibeam maser survey II. Statistical analysis & Galactic distribution of 6668-MHz methanol masers
- Author
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Jeremy Yates, Gary A. Fuller, Adam Avison, J. Cox, Antonio Chrysostomou, Michael G. Burton, Anita M. S. Richards, P. J. Diamond, J. A. Green, Andrew Walsh, Chris Phillips, Naomi McClure-Griffiths, Simon Ellingsen, Shari Breen, Melvin Hoare, L. Quinn, Malcolm Gray, M. R. W. Masheder, Mark Thompson, Kate Brooks, M. A. Voronkov, M. R. Pestalozzi, Derek Ward-Thompson, and D. Wong-McSweeney
- Subjects
Astrophysics::High Energy Astrophysical Phenomena ,Population ,Flux ,Astrophysics ,F500 ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,Protostar ,Astrophysics::Solar and Stellar Astrophysics ,Maser ,education ,010303 astronomy & astrophysics ,Southern Hemisphere ,Luminosity function ,Astrophysics::Galaxy Astrophysics ,Physics ,education.field_of_study ,010308 nuclear & particles physics ,Astronomy ,Astronomy and Astrophysics ,Galactic plane ,Galaxy ,Space and Planetary Science - Abstract
The Methanol Multibeam survey has produced the largest and most complete census of methanol and excited-state hydroxyl masers in the Galaxy to date. Observing the entire Galactic plane visible from the Southern hemisphere for 6668-MHz methanol and 6030/6035-MHz hydroxyl masers, to a rms sensitivity of 0.015 Jy km s−1, the survey has detected a total of 972 methanol maser sources, implying a total Galactic population of ∼ 1290 sources with flux densities above the survey 3-σ peak flux density limit of 0.51 Jy. We present here the statistical properties of the methanol detections of the survey, including distributions in flux density, variability, and range of source velocities. The data suggest that the weaker masers exhibit greater variability. We also present an analysis of the Galactic distribution of 6668-MHz methanol masers. For theGalactic distribution, we present kinematic distance resolutions to an additional 202 sources to those published previously, and collate these with previous allocations, as well as exploring a recent Bayesian distance approach based on maser parallaxes to separately determine distances. We examine Galactic structure and determine the luminosity function of the Galactic population of methanol masers. We find that more luminous masers have an evenly distributed wide range of velocity widths compared with less luminous masers being dominated by narrow velocity ranges, with the implication that this may be tied to the evolution of the host protostar(s). We also see an indication that brighter sources are seen towards the arm origins.
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- 2017
25. Distances of Stars by mean of the Phase-lag Method
- Author
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D. Engels, Sandra Etoka, Anita M. S. Richards, and Eric Gérard
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Physics ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,Metallicity ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Circumstellar envelope ,01 natural sciences ,Monitoring program ,Galaxy ,Radio telescope ,Stars ,Astrophysics - Solar and Stellar Astrophysics ,Space and Planetary Science ,Angular diameter ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Asymptotic giant branch ,Astrophysics::Earth and Planetary Astrophysics ,010303 astronomy & astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Astrophysics::Galaxy Astrophysics - Abstract
Variable OH/IR stars are Asymptotic Giant Branch (AGB) stars with an optically thick circumstellar envelope that emit strong OH 1612 MHz emission. They are commonly observed throughout the Galaxy but also in the LMC and SMC. Hence, the precise inference of the distances of these stars will ultimately result in better constraints on their mass range in different metallicity environments. Through a multi-year long-term monitoring program at the Nancay Radio telescope (NRT) and a complementary high-sensitivity mapping campaign at the eMERLIN and JVLA to measure precisely the angular diameter of the envelopes, we have been re-exploring distance determination through the phase-lag method for a sample of stars, in order to refine the poorly-constrained distances of some and infer the currently unknown distances of others. We present here an update of this project., 4 pages, 1 figure, 2 tables, to appear in the Proceedings of the IAU Symposium No. 336: Astrophysical Masers: Unlocking the Mysteries of the Universe
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- 2017
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26. ALMA Discovery of Dust Belts around Proxima Centauri
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Guillem Anglada-Escudé, Itziar de Gregorio-Monsalvo, José L. Gómez, E. Rodriguez, M. J. López-González, Z. M. Berdiñas, Jose L. Ortiz, Ignasi Ribas, Cristina Rodríguez-López, Mayra Osorio, José F. Gómez, Pedro J. Amado, Enrique Macías, Guillem Anglada, James S. Jenkins, Anita M. S. Richards, Izaskun Jiménez-Serra, Manuel López-Puertas, Antxon Alberdi, Luisa Lara, Nicolás Morales, and Miguel A. Pérez-Torres
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Physics ,Earth and Planetary Astrophysics (astro-ph.EP) ,010308 nuclear & particles physics ,Astronomy ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Planetary system ,planetary systems [radio continuum] ,01 natural sciences ,circumstellar matter ,Space and Planetary Science ,0103 physical sciences ,Physics::Space Physics ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,010303 astronomy & astrophysics ,planetary systems ,individual (Proxima Centauri) [stars] ,Astrophysics::Galaxy Astrophysics ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Proxima Centauri, the star closest to our Sun, is known to host at least one terrestrial planet candidate in a temperate orbit. Here we report the ALMA detection of the star at 1.3 mm wavelength and the discovery of a belt of dust orbiting around it at distances ranging between 1 and 4 au, approximately. Given the low luminosity of the Proxima Centauri star, we estimate a characteristic temperature of about 40 K for this dust, which might constitute the dust component of a small-scale analog to our solar system Kuiper belt. The estimated total mass, including dust and bodies up to 50 km in size, is of the order of 0.01 Earth masses, which is similar to that of the solar Kuiper belt. Our data also show a hint of warmer dust closer to the star. We also find signs of two additional features that might be associated with the Proxima Centauri system, which, however, still require further observations to be confirmed: an outer extremely cold (about 10 K) belt around the star at about 30 au, whose orbital plane is tilted about 45 degrees with respect to the plane of the sky; and additionally, we marginally detect a compact 1.3 mm emission source at a projected distance of about 1.2 arcsec from the star, whose nature is still unknown., 9 pages, 4 figures, accepted for publication in The Astrophysical Journal Letters
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- 2017
27. The close circumstellar environment of Betelgeuse - V. Rotation velocity and molecular envelope properties from ALMA
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Keiichi Ohnaka, Pierre Kervella, E. O'Gorman, Leen Decin, Iain McDonald, Graham M. Harper, Anita M. S. Richards, Ward Homan, Miguel Montargès, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institute of Astronomy [Leuven], Catholic University of Leuven - Katholieke Universiteit Leuven (KU Leuven), Jodrell Bank Centre for Astrophysics (JBCA), University of Manchester [Manchester], Center for Astrophysics and Space Astronomy [Boulder] (CASA), University of Colorado [Boulder], Dublin Institute for Advanced Studies (DIAS), Instituto de Astronomıa, universidad catolica del Norte, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Jodrell Bank Centre for Astrophysics, Laboratoire d'études spatiales et d'instrumentation en astrophysique ( LESIA ), Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de Paris-Université Paris Diderot - Paris 7 ( UPD7 ) -Centre National de la Recherche Scientifique ( CNRS ), Katholieke Universiteit Leuven ( KU Leuven ), Center for Astrophysics and Space Astronomy [Boulder] ( CASA ), University of Colorado Boulder [Boulder], and Dublin Institute for Advanced Studies ( DIAS )
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Rotation period ,010504 meteorology & atmospheric sciences ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,circumstellar matter [Stars] ,0103 physical sciences ,Astrophysics::Solar and Stellar Astrophysics ,Red supergiant ,Solar and Stellar Astrophysics ,010303 astronomy & astrophysics ,Chromosphere ,Astrophysics::Galaxy Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,0105 earth and related environmental sciences ,Convection cell ,Physics ,Betelgeuse ,[SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR] ,individual: Betelgeuse [Stars] ,Astronomy and Astrophysics ,Radius ,Position angle ,rotation [Stars] ,high angular resolution [Techniques] ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,imaging [Stars] ,Astrophysics::Earth and Planetary Astrophysics ,Supergiant ,supergiants [Stars] ,[ SDU.ASTR.SR ] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR] - Abstract
We observed Betelgeuse using ALMA's extended configuration in band 7 (f~340 GHz, {\lambda}~0.88 mm), resulting in a very high angular resolution of 18 mas. Using a solid body rotation model of the 28SiO(v=2,J=8-7) line emission, we show that the supergiant is rotating with a projected equatorial velocity of v_eq sin i = 5.47 +/- 0.25 km/s at the equivalent continuum angular radius R_star = 29.50 +/- 0.14 mas. This corresponds to an angular rotation velocity of {\omega} sin i = (5.6 +/- 1.3) x 10^(-9) rad/s. The position angle of its north pole is PA = 48.0 +/- 3.5{\deg}. The rotation period of Betelgeuse is estimated to P/sin i = 36 +/- 8 years. The combination of our velocity measurement with previous observations in the ultraviolet shows that the chromosphere is co-rotating with the star up to a radius of ~10 au (45 mas or 1.5x the ALMA continuum radius). The coincidence of the position angle of the polar axis of Betelgeuse with that of the major ALMA continuum hot spot, a molecular plume, and a partial dust shell (from previous observations) suggests that focused mass loss is currently taking place in the polar region of the star. We propose that this hot spot corresponds to the location of a particularly strong "rogue" convection cell, which emits a focused molecular plume that subsequently condenses into dust at a few stellar radii. Rogue convection cells therefore appear to be an important factor shaping the anisotropic mass loss of red supergiants., Comment: 18 pages, 19 figures, accepted for publication in A&A, update of bibliography and acknowledgements
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- 2017
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28. SS433's Jet Trace from ALMA Imaging and Global Jet Watch Spectroscopy: Evidence for Post-launch Particle Acceleration
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Anita M. S. Richards, Robert Laing, Steven Lee, and Katherine M. Blundell
- Subjects
astro-ph.HE ,High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,Jet (fluid) ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,01 natural sciences ,Submillimeter Array ,Magnetic field ,010309 optics ,Particle acceleration ,Stars ,symbols.namesake ,Space and Planetary Science ,0103 physical sciences ,Faraday effect ,symbols ,Astrophysics - High Energy Astrophysical Phenomena ,Ejecta ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Line (formation) - Abstract
We present a comparison of Doppler-shifted H-alpha line emission observed by the Global Jet Watch from freshly-launched jet ejecta at the nucleus of the Galactic microquasar SS433 with subsequent ALMA imaging at mm-wavelengths of the same jet ejecta. There is a remarkable similarity between the transversely-resolved synchrotron emission and the prediction of the jet trace from optical spectroscopy: this is an a priori prediction not an a posteriori fit, confirming the ballistic nature of the jet propagation. The mm-wavelength of the ALMA polarimetry is sufficiently short that the Faraday rotation is negligible and therefore that the observed E-vector directions are accurately orthogonal to the projected local magnetic field. Close to the nucleus the B-field vectors are perpendicular to the direction of propagation. Further out from the nucleus, the B-field vectors that are coincident with the jet instead become parallel to the ridge line; this occurs at a distance where the jet bolides are expected to expand into one another. X-ray variability has also been observed at this location; this has a natural explanation if shocks from the expanding and colliding bolides cause particle acceleration. In regions distinctly separate from the jet ridge line, the fractional polarisation approaches the theoretical maximum for synchrotron emission., Comment: To appear in ApJ Letters
- Published
- 2018
29. OH MASERS TOWARDS THE W49A STAR-FORMING REGION WITH MERLIN AND e-MERLN OBSERVATIONS
- Author
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K. Asanok, Anita M. S. Richards, Malcolm Gray, Sandra Etoka, B. Kramer, and N. Gasiprong
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Very large array ,Epoch (astronomy) ,Star formation ,Astronomy ,General Medicine ,Astrophysics ,Star (graph theory) ,law.invention ,Interferometry ,Geography ,law ,OH/IR star ,Maser ,MERLIN - Abstract
We present preliminary results from OH ground state phase referenced observations carried out with the Multi Element Radio Linked Interferometer Network (MERLIN) and e-MERLIN towards the massive star forming region W49A. There are three active SFRs within this complex: W49 North (W49 N), W49 South (W49 S) and W49 South West (W49 SW). The rst epoch of observations was obtained in 2005 with MERLIN while the second epoch was obtained in 2013 with the e-MERLIN upgraded system. In this paper, we present 1665 and 1720 MHz maser emission towards W49 S and W49 SW. Overall, both epochs show good agreement with the previous observations of Argon et al. (2000) carried out with the Very Large Array (VLA). The better sensitivity and wider velocity coverage of the MERLIN/e-MERLIN observations allowed us to discover a new 1720 MHz OH maser site in W49 S.
- Published
- 2015
30. Polarization morphology of SiO masers in the circumstellar envelope of the asymptotic giant branch star R Cassiopeiae
- Author
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Anita M. S. Richards, Philip J. Diamond, Malcolm Gray, and K. Assaf
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Physics ,Photosphere ,Polarization in astronomy ,Linear polarization ,Astronomy and Astrophysics ,Circumstellar envelope ,Astrophysics ,Polarization (waves) ,symbols.namesake ,Space and Planetary Science ,Faraday effect ,symbols ,Astrophysics::Solar and Stellar Astrophysics ,Asymptotic giant branch ,Astrophysics::Galaxy Astrophysics ,Circular polarization - Abstract
Silicon monoxide maser emission has been detected in the circumstellar envelopes of many evolved stars in various vibrationally-excited rotational transitions. It is considered a good tracer of the wind dynamics close to the photosphere of the star. We have investigated the polarization morphology in the circumstellar envelope of an AGB star, R Cas. We mapped the linear and circular polarization of SiO masers in the v=1, J=1-0 transition. The linear polarization is typically a few tens of percent while the circular polarization is a few percent. The fractional polarization tends to be higher for emission of lower total intensity. We found that, in some isolated features the fractional linear polarization appears to exceed 100%. We found the Faraday rotation is not negligible but is ~15 deg., which could produce small scale structure in polarized emission whilst total intensity is smoother and partly resolved out. The polarization angles vary considerably from feature to feature but there is a tendency to favour the directions parallel or perpendicular to the radial direction with respect to the star. In some features, the polarization angle abruptly flips 90 deg. We found that our data are in the regime where the model of Goldreich et al (1973) can be applied and the polarization angle flip is caused when the magnetic field is at close to 55 deg. to the line of sight. The polarization angle configuration is consistent with a radial magnetic field although other configurations are not excluded.
- Published
- 2013
31. ALMA observations of the nearby AGB star L2 Puppis - I. Mass of the central star and detection of a candidate planet
- Author
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Iain McDonald, Anita M. S. Richards, W. Homan, Miguel Montargès, Leen Decin, Keiichi Ohnaka, and Pierre Kervella
- Subjects
Solar System ,Red giant ,individual: HD 56096 [Stars] ,Brown dwarf ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Planet ,0103 physical sciences ,Asymptotic giant branch ,Astrophysics::Solar and Stellar Astrophysics ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,Physics ,010308 nuclear & particles physics ,Astronomy and Astrophysics ,Circumstellar matter ,AGB and post-AGB [Stars] ,Planetary nebula ,Radial velocity ,Planetary systems ,detection [Planets and satellites] ,high angular resolution [Techniques] ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,Circumstellar dust ,Astrophysics::Earth and Planetary Astrophysics - Abstract
Six billion years from now, while evolving on the asymptotic giant branch (AGB), the Sun will metamorphose from a red giant into a beautiful planetary nebula. This spectacular evolution will impact the Solar System planets, but observational confirmations of the predictions of evolution models are still elusive as no planet orbiting an AGB star has yet been discovered. The nearby AGB red giant L2 Puppis (d = 64 pc) is surrounded by an almost edge-on circumstellar dust disk. We report new observations with ALMA at very high angular resolution (18 x 15 mas) in band 7 (f ~ 350 GHz) that allow us to resolve the velocity profile of the molecular disk. We establish that the gas velocity profile is Keplerian within the central cavity of the dust disk, allowing us to derive the mass of the central star L2 Pup A, mA = 0.659 +/- 0.011 +/- 0.041 Msun (+/- 6.6%). From evolutionary models, we determine that L2 Pup A had a near-solar main sequence mass, and is therefore a close analog of the future Sun in 5 to 6 Gyr. The continuum map reveals the presence of a secondary source (B) at a radius of 2 AU contributing fB/ fA = 1.3 +/- 0.1% of the flux of the AGB star. L2 Pup B is also detected in CO emission lines at a radial velocity of vB = 12.2 +/- 1.0 km/s. The close coincidence of the center of rotation of the gaseous disk with the position of the continuum emission from the AGB star allows us to constrain the mass of the companion to mB = 12 +/- 16 MJup. L2 Pup B is most likely a planet or low mass brown dwarf with an orbital period around 5 years. Its continuum brightness and molecular emission suggest that it may be surrounded by an extended molecular atmosphere or an accretion disk. L2 Pup therefore emerges as a promising vantage point on the distant future of our Solar System., Comment: 18 pages, 12 figures, Astronomy & Astrophysics, in press
- Published
- 2016
- Full Text
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32. Polarization properties of R Cas SiO masers
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Philip J. Diamond, Anita M. S. Richards, Malcolm Gray, and K. Assaf
- Subjects
Physics ,Space and Planetary Science ,law ,Astrophysics::Solar and Stellar Astrophysics ,Astronomy and Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Maser ,Molecular physics ,Astrophysics::Galaxy Astrophysics ,law.invention - Abstract
Silicon monoxide maser emission has been detected in the circumstellar envelopes of many evolved stars. It is a good tracer of the wind dynamics within a few stellar radii of the central star. We investigated the polarization morphology in the circumstellar envelope of an AGB star, R Cas, by using the VLBA to map the linear and circular polarization of the v=1, J=1-0 SiO maser transition during 23 epochs over two stellar cycles. The average fractional circular polarization is a few percent. The average fractional linear polarization per epoch is 11–58%, but some isolated features exceed 100%, probably because the total intensity emission is smoother and more resolved-out. The maser electric polarization vector angle has a preferrential tendency to be either parallel or perpendicular to the radial direction to the star.
- Published
- 2012
33. Masers in evolved star winds
- Author
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Anita M. S. Richards
- Subjects
Physics ,Late type ,Astronomy ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Star (graph theory) ,law.invention ,Space and Planetary Science ,law ,Astrophysics::Solar and Stellar Astrophysics ,Supergiant ,Maser ,Astrophysics::Galaxy Astrophysics - Abstract
This review summarises current observations of masers around evolved stars and models for their location and behaviour, followed by some of the many highlights from the past 5 years. Some of these have been the fruition of long-term monitoring, a vital aspect of study of stars which are both periodically variable and prone to rapid outbursts or transition to a new evolutionary stage. Interferometric imaging of masers provide the highest-resolution probes of the stellar wind, but their exponential amplification and variability means that multiple observations are needed to investigate questions such as what drives the wind from the stellar surface; why does it accelerate slowly over many tens of stellar radii; what causes maser variability. VLBI parallaxes have improved our understanding of individual objects and of Galactic populations. Masers from wide range of binary and post-AGB objects are accessible to sensitive modern instruments, including energetic symbiotic systems. Masers have been detected up to THz frequencies withHerscheland ALMA's ability to resolve a wide range of maser and thermal lines will provide accurate constraints on physical conditions including during dust formation.
- Published
- 2012
34. Flares and proper motions of ground-state OH masers in W75N
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Vincent L. Fish, Anita M. S. Richards, W. M. Goss, and Malcolm Gray
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Physics ,H II region ,Astrophysics::High Energy Astrophysical Phenomena ,Continuum (design consultancy) ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,law.invention ,Radio telescope ,Interferometry ,Space and Planetary Science ,law ,Astrophysics::Solar and Stellar Astrophysics ,Outflow ,Maser ,Astrophysics::Galaxy Astrophysics ,MERLIN ,Very Long Baseline Array - Abstract
The star-forming region W75N hosts bright OH masers that are observed to be variable. We present observations taken in 2008 of the ground-state OH maser transitions with the Very Long Baseline Array (VLBA) and the Multi-Element Radio-Linked Interferometer Network (MERLIN) and with the Nancay Radio Telescope in 2011. Several of the masers in W75N were observed to be flaring, with the brightest 1720-MHz maser in excess of 400 Jy. The 1720-MHz masers appear to be associated with the continuum source VLA 1, unlike the bright flaring 1665- and 1667-MHz masers, which are associated with VLA 2. The 1720-MHz masers are located in an outflow traced by water masers and are indicative of very dense molecular material near the H II region. The magnetic field strengths are larger in the 1720-MHz maser region than in most regions hosting only main-line OH masers. The density falls off along the outflow, and the order of appearance of different transitions of OH masers is consistent with theoretical models. The 1665- and 1667-MHz VLBA data are compared against previous epochs over a time baseline of over 7 years. The median maser motion is 3.5 km/s, with a scatter that is comparable to thermal turbulence. The general pattern of maser proper motions observed in the 1665- and 1667-MHz transitions is consistent with previous observations.
- Published
- 2011
35. QUASI-PERIODIC FORMALDEHYDE MASER FLARES IN THE MASSIVE PROTOSTELLAR OBJECT IRAS 18566+0408
- Author
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Stan Kurtz, Marta Sewilo, Luca Olmi, W. M. Goss, Peter Hofner, Anita M. S. Richards, H. Linz, and Esteban Araya
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Physics ,010504 meteorology & atmospheric sciences ,Infrared ,Formaldehyde ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,01 natural sciences ,Accretion (astrophysics) ,law.invention ,chemistry.chemical_compound ,chemistry ,13. Climate action ,Space and Planetary Science ,law ,Astrophysics of Galaxies (astro-ph.GA) ,0103 physical sciences ,Angular resolution ,Maser ,Quasi periodic ,010303 astronomy & astrophysics ,MERLIN ,0105 earth and related environmental sciences ,Line (formation) - Abstract
We report results of an extensive observational campaign of the 6 cm formaldehyde maser in the young massive stellar object IRAS18566+0408 (G37.55+0.20) conducted from 2002 to 2009. Using Arecibo, VLA, and GBT, we discovered quasi-periodic formaldehyde flares (P ~ 237 days). Based on Arecibo observations, we also discovered correlated variability between formaldehyde (H2CO) and methanol (CH3OH) masers. The H2CO and CH3OH masers are not spatially coincident, as demonstrated by different line velocities and high angular resolution MERLIN observations. The flares could be caused by variations in the infrared radiation field, possibly modulated by periodic accretion onto a young binary system., Comment: 16 pages, 3 figures, accepted for publication in the Astrophysical Journal Letters
- Published
- 2010
36. The diversity of methanol maser morphologies from VLBI observations
- Author
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H. J. van Langevelde, Ylva Pihlström, Marian Szymczak, Anna Bartkiewicz, and Anita M. S. Richards
- Subjects
Physics ,H II region ,European VLBI Network ,FOS: Physical sciences ,Astronomy and Astrophysics ,Torus ,Observable ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,law.invention ,Wavelength ,Space and Planetary Science ,law ,Astrophysics of Galaxies (astro-ph.GA) ,Very-long-baseline interferometry ,Astrophysics::Solar and Stellar Astrophysics ,Protostar ,Maser ,Astrophysics::Galaxy Astrophysics - Abstract
We investigate which structures the 6.7 GHz methanol masers trace in the environment of high-mass protostar candidates by observing a homogenous sample of methanol masers selected from Torun surveys. We also probed their origins by looking for associated H II regions and IR emission. We selected 30 methanol sources with improved position accuracies achieved using MERLIN and another 3 from the literature. We imaged 31 of these using the European VLBI Network's expanded array of telescopes with 5-cm (6-GHz) receivers. We used the VLA to search for 8.4 GHz radio continuum counterparts and inspected Spitzer GLIMPSE data at 3.6-8 um from the archive. High angular resolution images allowed us to analyze the morphology and kinematics of the methanol masers in great detail and verify their association with radio continuum and mid-infrared emission. A new class of "ring-like" methanol masers in star--forming regions appeared to be suprisingly common, 29 % of the sample. The new morphology strongly suggests that methanol masers originate in the disc or torus around a proto- or a young massive star. However, the maser kinematics indicate the strong influence of outflow or infall. This suggests that they form at the interface between the disc/torus and a flow. This is also strongly supported by Spitzer results because the majority of the masers coincide with 4.5 um emission to within less than 1 arcsec. Only four masers are associated with the central parts of UC H II regions. This implies that 6.7 GHz methanol maser emission occurs before H II region observable at cm wavelengths is formed., 32 pages, 10 tables, 6 figures, accepted for publication in A&A
- Published
- 2009
37. Turbulent, steamy red supergiant winds
- Author
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Indra Bains, Anna Bartkiewicz, Anita M. S. Richards, Marian Szymczak, Jeremy Yates, Malcolm Gray, E. Mendoza-Torres, H. J. van Langevelde, M. R. W. Masheder, R. J. Cohen, Sandra Etoka, Philip J. Diamond, Wouter Vlemmings, E. E. Lekht, and Koji Murakawa
- Subjects
Physics ,Turbulence ,Late type ,Astronomy ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,law.invention ,Supernova ,Space and Planetary Science ,law ,Very-long-baseline interferometry ,Astrophysics::Solar and Stellar Astrophysics ,Red supergiant ,Supergiant ,Maser ,Astrophysics::Galaxy Astrophysics ,Water vapor - Abstract
Rapidly-evolving red supergiants (RSG) lose half or more of their mass before ending their lives as supernovae. Masers allow us to study the mass loss from 4 nearby RSG in AU-scale detail using MERLIN and EVN/global VLBI. The water maser clouds are over-dense and over-magnetised with respect to the surrounding wind. In most cases, the brighter an individual maser component is the smaller its apparent (beamed) FWHM appears, as predicted for approximately spherical clouds. Individual water maser features have a typical half-life of 5-10 yr, but comparison with single dish monitoring suggests that the water vapour clouds themselves survive many decades (the water maser shell crossing time), within which the local masers wink on and off. OH mainline masers are found in the tenuous surrounding gas, overlapping the water maser shell, surrounded by OH 1612-MHz masers at a greater distance from the star.
- Published
- 2007
38. The 2014 Alma Long Baseline Campaign: First Results From High Angular Resolution Observations Toward The Hl Tau Region
- Author
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Tsuyoshi Sawada, Kouichiro Nakanishi, Laura M. Pérez, Stuartt Corder, Akihiko Hirota, Vincent Piétu, F. Morales, Paulo C. Cortes, Richard Hills, L. C. Watson, T. A. van Kempen, Alwyn Wootten, D. Garcia-Appadoo, Crystal L. Brogan, N. Marcelino, Seiji Kameno, Lizette Guzman-Ramirez, Remo P. J. Tilanus, K. Plarre, Robert Laing, S. Gonzalez, J. A. Rodón, Ed Fomalont, A. S. Hales, Jacqueline Hodge, Taehyun Jung, T. Kaminski, Elisabetta Liuzzo, H. Y. Liu, Carmen López, Catherine Vlahakis, Frédéric Gueth, John E. Hibbard, Gianni Marconi, G. Schieven, J. Gallardo, Todd R. Hunter, Rebeca Aladro, Stephane Leon, Yasutaka Kurono, Satoko Takahashi, I. Toledo, J. R. Cortes, L. Videla, F. Galarza, Eiji Akiyama, Denis Barkats, M. Radiszcz, Paola Andreani, L.-Å. Nyman, Leonardo Testi, Y. Asaki, Anita M. S. Richards, Anthony J. Remijan, Chin-Fei Lee, Satoki Matsushita, William R. F. Dent, Patricio Sanhueza, Ray A. Lucas, Neil M. Phillips, Jeffrey G. Mangum, I. de Gregorio-Monsalvo, Caterina M. V. Impellizzeri, E. Chapillon, Bojan Nikolic, Q. Nguyen Luong, Eric Villard, D. Broguiere, Alma Partnership, J. Di Francesco, Akiko Kawamura, J. Garcia, B. Vila Vilaro, Shigehisa Takakuwa, Ken'ichi Tatematsu, R. Kneissl, T. Hill, Daniel Espada, K. Saigo, Elizabeth Humphreys, H. Francke, Tommy Wiklind, A. Castro-Carrizo, C. Ubach, A. Mignano, National Radio Astronomy Observatory [Charlottesville] (NRAO), National Radio Astronomy Observatory (NRAO), National Radio Astronomy Observatory [Socorro] (NRAO), European Southern Observatory [Santiago] (ESO), European Southern Observatory (ESO), Joint ALMA Observatory (JAO), European Southern Observatory (ESO)-National Radio Astronomy Observatory (NRAO), Cavendish Laboratory, University of Cambridge [UK] (CAM), Institute of Space and Astronautical Science (ISAS), National Astronomical Observatory of Japan (NAOJ), INAF - Osservatorio Astronomico di Bologna (OABO), Istituto Nazionale di Astrofisica (INAF), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Centre National d'Études Spatiales [Toulouse] (CNES)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS), Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), Academia Sinica, Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Institut de RadioAstronomie Millimétrique (IRAM), Centre National de la Recherche Scientifique (CNRS), Korea Astronomy and Space Science Institute (KASI), Okayama University [Okayama], Leiden Observatory [Leiden], Universiteit Leiden [Leiden], AMOR 2015, Laboratoire d'Astrophysique de Bordeaux [Pessac] (LAB), Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Herzberg Institute of Astrophysics, National Research Council of Canada (NRC), Japan Aerospace Exploration Agency [Sagamihara] (JAXA), Institut de Planétologie et d'Astrophysique de Grenoble (IPAG ), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), and Okayama University
- Subjects
Physics ,Spectral index ,stars: formation ,LkHα358 ,[SDU.ASTR.CO]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO] ,protoplanetary disks ,Astronomy and Astrophysics ,submillimeter: planetary systems ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Position angle ,Submillimeter Array ,Spectral line ,Stars ,Wavelength ,stars: individual: HL Tau ,Space and Planetary Science ,techniques: interferometric ,XZ Tau ,stars: individual (HL Tau, XZ Tau, LkHα358) ,Protostar ,Astrophysics::Earth and Planetary Astrophysics ,Protoplanet ,Astrophysics::Galaxy Astrophysics - Abstract
著者人数: 84名, Accepted: 2015-03-17, 資料番号: SA1150147000
- Published
- 2015
39. Measuring Magnetic Fields Near and Far with the SKA via the Zeeman Effect
- Author
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Vincent L. Fish, A. P. Sarma, Sandra Etoka, James McBride, Albert A. Zijlstra, Timothy Robishaw, Wouter Vlemmings, James Green, Emmanuel Momjian, Anita M. S. Richards, B. Kramer, Gabriele Surcis, Tyler L. Bourke, Hiroshi Imai, and Malcolm Gray
- Subjects
Physics ,Zeeman effect ,Field (physics) ,Molecular cloud ,FOS: Physical sciences ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Magnetic field ,law.invention ,Interstellar medium ,symbols.namesake ,law ,Astrophysics of Galaxies (astro-ph.GA) ,Ionization ,symbols ,Physics::Atomic Physics ,Faraday cage ,Astrophysics::Galaxy Astrophysics - Abstract
The measurement of Zeeman splitting in spectral lines---both in emission and absorption---can provide direct estimates of the magnetic field strength and direction in atomic and molecular clouds, both in our own Milky Way and in external galaxies. This method will probe the magnetic field in the warm and cold neutral components of the interstellar medium, providing a complement to the extensive SKA Faraday studies planning to probe the field in the ionized components., Comment: 10 pages, 0 figures; to appear as part of 'Cosmic Magnetism' in Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)110
- Published
- 2015
40. Phase-lag distance of OH83.4-0.9 from eMERLIN and NRT observations
- Author
-
Sandra Etoka, D. Engels, E. Gerard, and Anita M. S. Richards
- Subjects
Physics ,Geodesy ,Phase lag - Published
- 2015
41. MERLIN and eMERLIN OH maser observations toward the star forming region complex W49 A
- Author
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K. Asanok, Sandra Etoka, Malcolm Gray, Anita M. S. Richards, B. Kramer, and N. Gasiprong
- Subjects
Physics ,Merlin (protein) ,law ,Astronomy ,Star (graph theory) ,Maser ,law.invention - Published
- 2015
42. Temporal Evolution of the Size and Temperature of Betelgeuse's Extended Atmosphere
- Author
-
Edward F. Guinan, Richard Wasatonic, Graham M. Harper, Alexander Brown, Wouter Vlemmings, E. O'Gorman, and Anita M. S. Richards
- Subjects
Shock wave ,010504 meteorology & atmospheric sciences ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Power law ,Photometry (optics) ,0103 physical sciences ,massive [Stars] ,Radiative transfer ,Astronomy, Astrophysics and Cosmology ,Astrophysics::Solar and Stellar Astrophysics ,atmospheres [Stars] ,010303 astronomy & astrophysics ,Very Long Baseline Array ,Astrophysics::Galaxy Astrophysics ,Solar and Stellar Astrophysics (astro-ph.SR) ,0105 earth and related environmental sciences ,Physics ,Betelgeuse ,mass-loss [Stars] ,individual: Betelgeuse [Stars] ,Astronomy and Astrophysics ,Wavelength ,Supergiants ,Astrophysics - Solar and Stellar Astrophysics ,13. Climate action ,Space and Planetary Science ,late-type [Stars] ,Circular symmetry ,Astrophysics::Earth and Planetary Astrophysics - Abstract
Spatially resolved multi-wavelength centimeter continuum observations of cool evolved stars can not only constrain the morphology of the radio emitting regions, but can also directly probe the mean gas temperature at various depths of the star's extended atmosphere. Here, we use the Very Large Array (VLA) in the A configuration with the Pie Town (PT) Very Long Baseline Array (VLBA) antenna to spatially resolve the extended atmosphere of Betelgeuse over multiple epochs at 0.7, 1.3, 2.0, 3.5, and 6.1 cm. The extended atmosphere deviates from circular symmetry at all wavelengths while at some epochs we find possible evidence for small pockets of gas significantly cooler than the mean global temperature. We find no evidence for the recently reported e-MERLIN radio hotspots in any of our multi-epoch VLA/PT data, despite having sufficient spatial resolution and sensitivity at short wavelengths, and conclude that these radio hotspots are most likely interferometric artefacts. The mean gas temperature of the extended atmosphere has a typical value of 3000 K at 2 R∗ and decreases to 1800 K at 6 R∗, in broad agreement with the findings of the single epoch study from Lim et al. (1998, Nature, 392, 575). The overall temperature profile of the extended atmosphere between 2 R∗ ≲ r ≲ 6 R∗ can be described by a power law of the form Tgas(r) ∝ r-0.6, with temporal variability of a few 100 K evident at some epochs. Finally, we present over 12 yr of V band photometry, part of which overlaps our multi-epoch radio data. We find a correlation between the fractional flux density variability at V band with most radio wavelengths. This correlation is likely due to shock waves induced by stellar pulsations, which heat the inner atmosphere and ionize the more extended atmosphere through radiative means. Stellar pulsations may play an important role in exciting Betelgeuse's extended atmosphere.
- Published
- 2015
- Full Text
- View/download PDF
43. The 2014 ALMA Long Baseline Campaign: Observations of Asteroid 3 Juno at 60 Kilometer Resolution
- Author
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Arielle Moullet, S. Gonzalez, Ed Fomalont, Taehyun Jung, J. Gallardo, Eric Villard, F. Morales, Lizette Guzman-Ramirez, Jacqueline Hodge, L. Videla, Paola Andreani, William R. F. Dent, Akihiko Hirota, F. Galarza, L. C. Watson, D. Broguiere, John E. Hibbard, Ken'ichi Tatematsu, Jeffrey G. Mangum, Alma Partnership, Y. Asaki, Anita M. S. Richards, J. Di Francesco, Carmen López, Richard Hills, A. Mignano, Seiji Kameno, J. R. Cortes, Catherine Vlahakis, Gianni Marconi, Anthony J. Remijan, Paulo C. Cortes, Rebeca Aladro, J. A. Rodón, Satoki Matsushita, Stephane Leon, R. Kneissl, Ray A. Lucas, D. Garcia-Appadoo, I. Toledo, H. Francke, Tsuyoshi Sawada, Caterina M. V. Impellizzeri, Tommy Wiklind, L.-Å. Nyman, Antonio Hales, T. Kaminski, Yasutaka Kurono, Satoko Takahashi, I. de Gregorio-Monsalvo, Bojan Nikolic, M. Radiszcz, K. Plarre, Crystal L. Brogan, Kouichiro Nakanishi, Robert Laing, N. Marcelino, Todd R. Hunter, Elisabetta Liuzzo, Denis Barkats, Laura M. Pérez, Suzanna K. Randall, Remo P. J. Tilanus, D. Espada, Neil M. Phillips, T. A. van Kempen, B. Vila Vilaro, J. Garcia, T. Hill, and Elizabeth Humphreys
- Subjects
Physics ,Rotation period ,Solar System ,minor planets, asteroids: individual (3 Juno) ,media_common.quotation_subject ,Subsolar point ,Astronomy and Astrophysics ,Astrophysics ,minor planets, asteroids: general ,planets and satellites: surfaces ,Submillimeter Array ,Asteroids ,Impact crater ,techniques: interferometric ,Space and Planetary Science ,Sky ,Asteroid ,Brightness temperature ,ALMA ,media_common ,Solar system - Abstract
著者人数: 69名, Accepted: 2015-03-13, 資料番号: SA1150146000
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- 2015
44. Maser Astrometry with VLBI and the SKA
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M. J. Reid, Simon Ellingsen, J. A. Green, Wouter Vlemmings, Andreas Brunthaler, Anita M. S. Richards, H. J. van Langevelde, and Hiroshi Imai
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Physics ,Star formation ,Milky Way ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy ,Local Group ,FOS: Physical sciences ,Astrophysics ,Astrometry ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,law.invention ,Stars ,law ,Astrophysics of Galaxies (astro-ph.GA) ,Very-long-baseline interferometry ,Astrophysics::Solar and Stellar Astrophysics ,Maser ,Astrophysics::Galaxy Astrophysics - Abstract
We discuss the unique opportunities for maser astrometry with the inclusion of the Square Kilometre Array (SKA) in Very Long Baseline Interferometry (VLBI) networks. The first phase of the SKA will enable observations of hydroxyl and methanol masers, positioning the latter to an accuracy of 5 microarcseconds, and the second phase may allow water maser observations. These observations will provide trigonometric distances with errors as small as 1%. The unrivalled sensitivity of the SKA will enable large-scale surveys and, through joint operations, will turn any VLBI network into a fast astrometry device. Both evolved stars and high mass star formation regions will be accessible throughout the (Southern) Milky Way, completing our understanding of the content, dynamics and history of our Galaxy. Maser velocities and proper motions will be measurable in the Local Group of galaxies and beyond, providing new insights into their kinematics and evolution., Comment: 9 pages, 1 figure, to appear in the Proceedings of "Advancing Astrophysics with the Square Kilometre Array" PoS(AASKA14)119
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- 2015
- Full Text
- View/download PDF
45. Special Session 6 Astronomical data management
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Robert J. Hanisch, Guenther Eichhorn, Françoise Genova, Anita M. S. Richards, Heinz Andernach, Robert C. Kennicutt, R. Elizabeth Griffin, Ajit K. Kembhavi, and Ray P. Norris
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Manifesto ,Legacy data ,business.industry ,General assembly ,Computer science ,media_common.quotation_subject ,Data management ,Best practice ,Astronomy and Astrophysics ,Virtual observatory ,Data science ,ComputingMilieux_GENERAL ,Space and Planetary Science ,Quality (business) ,Session (computer science) ,business ,media_common - Abstract
We present a summary of the major contributions to the Special Session on Astronomical Data Management held at the IAU XXVI General Assembly in Prague in 2006. While recent years have seen enormous improvements in access to astronomical data, and the Virtual Observatory aims to provide astronomers with seamless access to on-line resources, more attention needs to be paid to ensuring the quality and completeness of those resources. For example, data produced by telescopes are not always made available to the astronomical community, and new instruments are sometimes designed and built with insufficient planning for data management, while older but valuable legacy data often remain undigitised. Data and results published in journals do not always appear in the data centres, and astronomers in developing countries sometimes have inadequate access to on-line resources. To address these issues, an ‘Astronomers' Data Manifesto’ has been formulated with the aim of initiating a discussion that will lead to the development of a ‘code of best practice’ in astronomical data management.
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- 2006
46. A warped m= 2 water maser disc in V778 Cyg?
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Juri Poutanen, Natalia Babkovskaia, Anita M. S. Richards, and R. Szczerba
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Coupling ,Physics ,Astronomy and Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Radius ,Carbon star ,Silicate ,law.invention ,chemistry.chemical_compound ,chemistry ,Space and Planetary Science ,law ,Astrophysics::Solar and Stellar Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Binary system ,Maser ,Impact parameter ,Astrophysics::Galaxy Astrophysics ,Dust emission - Abstract
The silicate carbon star V778 Cyg is a source of 22 GHz water maser emission which was recently resolved by MERLIN. Observations revealed an elongated S-like structure along which the velocities of the maser features show a linear dependence on the impact parameter. This is consistent with a doubly-warped m=2 disc observed edge-on. Water masers and silicate dust emission (detected by IRAS and ISO) have a common origin in O-rich material and are likely to be co-located in the disc. We propose a detailed self-consistent model of a masing gas-dust disc around a companion to the carbon star in a binary system, which allows us to estimate the companion mass of 1.7 +- 0.1 M_sun, the disc radius of 40 +-3 AU and the distance between companions of about 80 AU. Using a dust-gas coupling model for water masing, we calculate the maser power self-consistently, accounting for both the gas and the dust energy balances. Comparing the simulation results with the observational data, we deduce the main physical parameters of the masing disc, such as the gas and dust temperatures and their densities. We also present an analysis of the stability of the disc.
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- 2006
47. SKA studies of nearby galaxies: star-formation, accretion processes and molecular gas across all environments
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Megan Argo, Susanne Aalto, T. W. B. Muxlow, Elias Brinks, Eric J. Murphy, A. Rushton, Miguel A. Pérez-Torres, Eva Schinnerer, Clive Dickinson, D Fenech, Michael W. Peel, John Conway, Anita M. S. Richards, A. Alberdi, I. van Bemmel, Robert Beswick, Malcolm Gray, and H. R. Kloeckner
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Physics ,Cosmology and Nongalactic Astrophysics (astro-ph.CO) ,Molecular line ,Star formation ,Astrophysics::High Energy Astrophysical Phenomena ,Astrophysics::Instrumentation and Methods for Astrophysics ,Astronomy ,FOS: Physical sciences ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics - Astrophysics of Galaxies ,Galaxy ,Accretion (astrophysics) ,Astrophysics of Galaxies (astro-ph.GA) ,Surface brightness ,Astrophysics::Galaxy Astrophysics ,Astrophysics - Cosmology and Nongalactic Astrophysics - Abstract
The SKA will be a transformational instrument in the study of our local Universe. In particular, by virtue of its high sensitivity (both to point sources and diffuse low surface brightness emission), angular resolution and the frequency ranges covered, the SKA will undertake a very wide range of astrophysical research in the field of nearby galaxies. By surveying vast numbers of nearby galaxies of all types with $\mu$Jy sensitivity and sub-arcsecond angular resolutions at radio wavelengths, the SKA will provide the cornerstone of our understanding of star-formation and accretion activity in the local Universe. In this chapter we outline the key continuum and molecular line science areas where the SKA, both during phase-1 and when it becomes the full SKA, will have a significant scientific impact., Comment: 23 pages, 4 figures, to appear as part of 'Continuum Science' in Proceedings 'Advancing Astrophysics with the Square Kilometre Array' PoS(AASKA14)070
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- 2014
48. OH Megamasers, Starburst and AGN Activity in Markarian 231
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J. A. Yates, Johan H. Knapen, J. L. Collett, Anita M. S. Richards, David J. Field, R. J. Cohen, Malcolm Gray, and M. M. Wright
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Physics ,Astrophysics::High Energy Astrophysical Phenomena ,Semi-major axis ,Astrophysics (astro-ph) ,FOS: Physical sciences ,Astronomy and Astrophysics ,Torus ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics ,Galaxy ,law.invention ,Magnetic field ,Space and Planetary Science ,law ,Astrophysics::Solar and Stellar Astrophysics ,Maser ,Astrophysics::Galaxy Astrophysics - Abstract
We present MERLIN observations of OH maser and radio continuum emission from the Ultra Luminous IR Galaxy Markarian 231. The 1665- and 1667-MHz transitions have a combined velocity extent of 720 km/s and show a similar position-velocity structure including a gradient of 1.7 km/s/pc from NW to SE along the 420-pc major axis, steeper in the inner few tens of pc. The maser distribution is modelled as a torus rotating about an axis inclined at ~45deg. We estimate the enclosed mass density to be 320(90) Msun in a flattened distribution, including a central unresolved mass of /=1E+05 K, giving a maser gain of, Comment: 16 pages, 7 figures
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- 2005
49. Magnetic field in Cepheus A as deduced from OH maser polarimetric observations
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Anita M. S. Richards, R. J. Cohen, Anna Bartkiewicz, and Marian Szymczak
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Physics ,H II region ,Zeeman effect ,Linear polarization ,Astrophysics (astro-ph) ,Polarimetry ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Polarization (waves) ,Magnetic field ,law.invention ,symbols.namesake ,Space and Planetary Science ,law ,symbols ,Astrophysics::Solar and Stellar Astrophysics ,Maser ,Astrophysics::Galaxy Astrophysics - Abstract
We present the results of MERLIN polarization mapping of OH masers at 1665 and 1667 MHz towards the Cepheus A star-forming region. The maser emission is spread over a region of 6 arcsec by 10 arcsec, twice the extent previously detected. In contrast to the 22 GHz water masers, the OH masers associated with H II regions show neither clear velocity gradients nor regular structures. We identified ten Zeeman pairs which imply a magnetic field strength along the line-of-sight from -17.3 to +12.7 mG. The magnetic field is organised on the arcsecond scale, pointing towards us in the west and away from us in the east side. The linearly polarized components, detected for the first time, show regularities in the polarization position angles depending on their position. The electric vectors of OH masers observed towards the outer parts of H II regions are consistent with the interstellar magnetic field orientation, while those seen towards the centres of H II regions are parallel to the radio-jets. A Zeeman quartet inside a southern H II region has now been monitored for 25 years; we confirm that the magnetic field decays monotonically over that period., Comment: 10 pages, 6 figures,accepted for publication in MNRAS
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- 2005
50. High-resolution studies of radio sources in theHubble DeepandFlanking Fields
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David J. Axon, E. A. Richards, T. W. B. Muxlow, Peter N. Wilkinson, Simon Garrington, K. I. Kellermann, Edward B. Fomalont, B. Anderson, Rogier A. Windhorst, Anita M. S. Richards, and R. B. Partridge
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Physics ,Astrophysics (astro-ph) ,Radio flux ,FOS: Physical sciences ,Flux ,High resolution ,Astronomy and Astrophysics ,Astrophysics ,Rms noise ,Redshift ,Galaxy ,Space and Planetary Science ,Flanking maneuver ,MERLIN - Abstract
Eighteen days of MERLIN data and 42 hours of A-array VLA data at 1.4 GHz have been combined to image a 10-arcmin field centred on the Hubble Deep and Flanking Fields (HDF and HFF). A complete sample of 92 radio sources with 1.4-GHz flux densities above 40 microJy has been imaged using MERLIN+VLA. The images are amongst the most sensitive yet made at 1.4 GHz, with rms noise levels of 3.3 microJy/beam in the 0.2-arcsec images. Virtually all the sources are resolved, with angular sizes in the range 0.2 to 3 arcsec. No additional sources were detected down to 23 microJy in the central 3 arcmin, indicating that sources fainter than 40 microJy are heavily resolved with MERLIN and must have typical angular sizes greater than 0.5 arcsec. Compact radio sources were used to align the optical data to the ICRF, to, Accepted by MNRAS Jan 2005 34 pp with inline b/w figures plus 9 pp of colour figures All material is available from http://www.merlin.ac.uk/HDF/ as gzipped PDFs. ME547.pdf.gz - main paper ME547_Appendix_C1.pdf.gz, ME547_Appendix_C2.pdf.gz - colour figures All figures are also available in png form
- Published
- 2005
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