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1. First long-term study of the Venus' Cloud Discontinuity with uninterrupted observations

Author

Javier Peralta, António Cidadão, Luigi Morrone, Clyde Foster, Mark Bullock, Eliot F. Young, Itziar Garate-Lopez, Agustín Sánchez-Lavega, Takeshi Horinouchi, Takeshi Imamura, Emmanuel Kardasis, Atsushi Yamazaki, and Shigeto Watanabe

Abstract

The discontinuity/disruption is a recurrent atmospheric wave observed to propagate during decades at the deeper clouds of Venus (47-56 km above the surface), while its absence at the top of the clouds (~70 km) suggests that it might dissipate at the upper clouds and contribute to the puzzling atmospheric superrotation through wave-mean flow interaction.Thanks to a campaign of ground-based observations performed in coordination with JAXA's Akatsuki mission since December 2021 until July 2022, we aimed to undertake the longest uninterrupted monitoring of the cloud discontinuity up to date to obtain a pioneering long-term characterization of its main properties and better constrain its recurrence and lifetime. The dayside upper, middle and nightside lower clouds were studied with images taken with suitable filters acquired by Akatsuki/UVI, amateur observers and NASA's IRTF/SpeX, respectively. Hundreds of images were inspected in search of discontinuity events and to measure properties like its dimensions, orientation or rotation period.We succeeded in tracking the discontinuity at the middle clouds during 109 days without interruption. The discontinuity exhibited properties nearly identical to measurements in 2016 and 2020, with an orientation of 91º±8º, length of 4100±800, width of 500±100 km and a rotation period of 5.11±0.09 days. Ultraviolet images during 13-14 June 2022 suggest that we have witnessed for the first time a manifestation of the discontinuity at the top of the clouds during ~21 hours, facilitated by an altitude change in the critical level for this wave due to slower zonal winds.

Published
2023
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2. The Rise and Fall of the King: The Correlation between FO Aquarii's Low States and the White Dwarf's Spindown

Author

Stephen M. Brincat, Enrique de Miguel, Richard Sabo, John Briol, Valery Tsehmeystrenko, B. Harris, Jean-Francois Gout, Franz-Josef Hambsch, Colin Littlefield, Charles Galdies, Greg Bolt, Jonathan Kemp, Nathan Krumm, D. Lemay, Teofilo Arranz Heras, George Sjoberg, Jeff Thrush, Gordon Myers, Emmanuel Kardasis, Michel Bonnardeau, Velimir A. Popov, Emil Pellett, Rob Solomon, Daniel Coulter, Robert A. Stiller, G. Walker, Geoffrey Stone, Stefano Padovan, Roger D. Pickard, Joseph Patterson, Peter F. Nelson, William Stein, James R. Foster, Peter M. Garnavich, Michelle Dadighat, Andre Debackere, Kevin B. Alton, Tonny Vanmunster, James Boardman, David Cejudo Fernandez, K. Graham, Mark Kennedy, Brad Vietje, William N. Goff, Pablo Lewin, Bradley S. Walter, Lewis M. Cook, David J. Lane, and Shawn Dvorak

Subjects
Physics, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astronomical sciences, Stellar astronomy and planetary systems, White dwarf, FOS: Physical sciences, Astronomy and Astrophysics, 22 Física, Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Spin-½
Abstract

The intermediate polar FO Aquarii (FO Aqr) experienced its first-reported low-accretion states in 2016, 2017, and 2018, and using newly available photographic plates, we identify pre-discovery low states in 1965, 1966, and 1974. The primary focus of our analysis, however, is an extensive set of time-series photometry obtained between 2002 and 2018, with particularly intensive coverage of the 2016-2018 low states. After computing an updated spin ephemeris for the white dwarf (WD), we show that its spin period began to increase in 2014 after having spent 27 years decreasing; no other intermediate polar has experienced a sign change of its period derivative, but FO Aqr has now done so twice. Our central finding is that the recent low states all occurred shortly after the WD began to spin down, even though no low states were reported in the preceding quarter-century, when it was spinning up. Additionally, the system's mode of accretion is extremely sensitive to the mass-transfer rate, with accretion being almost exclusively disk-fed when FO Aqr is brighter than V~14 and substantially stream-fed when it is not. Even in the low states, a grazing eclipse remains detectable, confirming the presence of a disk-like structure (but not necessarily a Keplerian accretion disk). We relate these various observations to theoretical predictions that during the low state, the system's accretion disk dissipates into a non-Keplerian ring of diamagnetic blobs. Finally, a new XMM-Newton observation from a high state in 2017 reveals an anomalously soft X-ray spectrum and diminished X-ray luminosity compared to pre-2016 observations., Comment: Accepted for publication in ApJ

Published
2019
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3. The First Post-Kepler Brightness Dips of KIC 8462852

Author

Tabetha. S. Boyajian, Roi Alonso, Alex Ammerman, David Armstrong, A. Asensio Ramos, K. Barkaoui, Thomas G. Beatty, Z. Benkhaldoun, Paul Benni, Rory O. Bentley, Andrei Berdyugin, Svetlana Berdyugina, Serge Bergeron, Allyson Bieryla, Michaela G. Blain, Alicia Capetillo Blanco, Eva H. L. Bodman, Anne Boucher, Mark Bradley, Stephen M. Brincat, Thomas G. Brink, John Briol, David J. A. Brown, J. Budaj, A. Burdanov, B. Cale, Miguel Aznar Carbo, R. Castillo García, Wendy J Clark, Geoffrey C. Clayton, James L. Clem, Phillip H Coker, Evan M. Cook, Chris M. Copperwheat, J. L. Curtis, R. M. Cutri, B. Cseh, C. H. Cynamon, Alex J. Daniels, James R. A. Davenport, Hans J. Deeg, Roberto De Lorenzo, Thomas de Jaeger, Jean-Bruno Desrosiers, John Dolan, D. J. Dowhos, Franky Dubois, R. Durkee, Shawn Dvorak, Lynn Easley, N. Edwards, Tyler G. Ellis, Emery Erdelyi, Steve Ertel, Rafael. G. Farfán, J. Farihi, Alexei V. Filippenko, Emma Foxell, Davide Gandolfi, Faustino Garcia, F. Giddens, M. Gillon, Juan-Luis González-Carballo, C. González-Fernández, J. I. González Hernández, Keith A. Graham, Kenton A. Greene, J. Gregorio, Na’ama Hallakoun, Ottó Hanyecz, G. R. Harp, Gregory W. Henry, E. Herrero, Caleb F. Hildbold, D. Hinzel, G. Holgado, Bernadett Ignácz, Ilya Ilyin, Valentin D. Ivanov, E. Jehin, Helen E. Jermak, Steve Johnston, S. Kafka, Csilla Kalup, Emmanuel Kardasis, Shai Kaspi, Grant M. Kennedy, F. Kiefer, C. L. Kielty, Dennis Kessler, H. Kiiskinen, T. L. Killestein, Ronald A. King, V. Kollar, H. Korhonen, C. Kotnik, Réka Könyves-Tóth, Levente Kriskovics, Nathan Krumm, Vadim Krushinsky, E. Kundra, Francois-Rene Lachapelle, D. LaCourse, P. Lake, Kristine Lam, Gavin P. Lamb, Dave Lane, Marie Wingyee Lau, Pablo Lewin, Chris Lintott, Carey Lisse, Ludwig Logie, Nicolas Longeard, M. Lopez Villanueva, E. Whit Ludington, A. Mainzer, Lison Malo, Chris Maloney, A. Mann, A. Mantero, Massimo Marengo, Jon Marchant, M. J. Martínez González, Joseph R. Masiero, Jon C. Mauerhan, James McCormac, Aaron McNeely, Huan Y. A. Meng, Mike Miller, Lawrence A. Molnar, J. C. Morales, Brett M. Morris, Matthew W. Muterspaugh, David Nespral, C. R. Nugent, Katherine M. Nugent, A. Odasso, Derek O’Keeffe, A. Oksanen, John M. O’Meara, András Ordasi, Hugh Osborn, John J. Ott, J. R. Parks, Diego Rodriguez Perez, Vance Petriew, R Pickard, András Pál, P. Plavchan, Don Pollacco, F. Pozo Nuñez, F. J. Pozuelos, Steve Rau, Seth Redfield, Howard Relles, Ignasi Ribas, Jon Richards, Joonas L. O. Saario, Emily J. Safron, J. Martin Sallai, Krisztián Sárneczky, Bradley E. Schaefer, Clea F. Schumer, Madison Schwartzendruber, Michael H. Siegel, Andrew P. V. Siemion, Brooke D. Simmons, Joshua D. Simon, S. Simón-Díaz, Michael L. Sitko, Hector Socas-Navarro, Á. Sódor, Donn Starkey, Iain A. Steele, Geoff Stone, Klaus G. Strassmeier, R. A. Street, Tricia Sullivan, J. Suomela, J. J. Swift, Gyula M. Szabó, Róbert Szabó, Róbert Szakáts, Tamás Szalai, Angelle M. Tanner, B. Toledo-Padrón, Tamás Tordai, Amaury H. M. J. Triaud, Jake D. Turner, Joseph H. Ulowetz, Marian Urbanik, Siegfried Vanaverbeke, Andrew Vanderburg, Krisztián Vida, Brad P. Vietje, József Vinkó, K. von Braun, Elizabeth O. Waagen, Dan Walsh, Christopher A. Watson, R. C. Weir, Klaus Wenzel, C. Westendorp Plaza, Michael W. Williamson, Jason T. Wright, M. C. Wyatt, WeiKang Zheng, Gabriella Zsidi, King‘s College London, Space Sciences, Technologies and Astrophysics Research Institute (STAR), Université de Liège, Université Cadi Ayyad [Marrakech] (UCA), Laboratoire d'Electrochimie et de Physico-chimie des Matériaux et des Interfaces (LEPMI ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut de Chimie du CNRS (INC)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Department of Physics and Astronomy [BatonRouge] (LSU), Louisiana State University (LSU), Laboratoire d'océanographie de Villefranche (LOV), Observatoire océanologique de Villefranche-sur-mer (OOVM), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Shed of Science Observatory, Department of Physics and Astronomy [Leicester], University of Leicester, Tennessee State University, Lomonosov Moscow State University (MSU), Institut d'Astrophysique et de Géophysique [Liège], Laboratoire de Génie de la Conception (LGeco), Institut National des Sciences Appliquées - Strasbourg (INSA Strasbourg), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA), Kuopio Unit [FMI], Finnish Meteorological Institute (FMI), Astrophysics Research Institute [Liverpool] (ARI), Liverpool John Moores University (LJMU), Observatoire astronomique de Strasbourg (ObAS), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de la Corogne, UDC, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Canada-France-Hawaii Telescope Corporation (CFHT), National Research Council of Canada (NRC)-Centre National de la Recherche Scientifique (CNRS)-University of Hawai'i [Honolulu] (UH), Duke Physics, Duke University [Durham], Instituto Andaluz de Geofísica y Prevención de Desastres Sísmicos [Granada] (IAGPDS), Universidad de Granada (UGR), National University of Ireland [Galway] (NUI Galway), Nyrölä Observatory (NYTT), Laboratoire d'Astrophysique de Marseille (LAM), Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Konkoly Observatory, Research Centre for Astronomy and Earth Sciences [Budapest], Hungarian Academy of Sciences (MTA)-Hungarian Academy of Sciences (MTA), Physical Oceanography and Instrumentation, Leibniz Institute for Baltic Sea Research Warnemünde, Instituto de Astrofisica de Canarias (IAC), Geophysical Laboratory [Carnegie Institution], Carnegie Institution for Science [Washington], High Speed Networks Laboratory, Dept. of Telecommunications and Media Informatics, Budapest University of Technology and Economics [Budapest] (BME), Medical University of South Carolina [Charleston] (MUSC), Department of Astronomy [Berkeley], University of California [Berkeley], University of California-University of California, Universidad de Granada = University of Granada (UGR), Carnegie Institution for Science, University of California [Berkeley] (UC Berkeley), and University of California (UC)-University of California (UC)

Subjects
Brightness, Single process, stars: peculia, Astronomy, FOS: Physical sciences, Astrophysics, 01 natural sciences, Kepler, Photometry (optics), 0103 physical sciences, stars: activity, comets: general, stars: individual (KIC 8462852), Astronomy and Astrophysics, Space and Planetary Science, 010306 general physics, 010303 astronomy & astrophysics, ComputingMilieux_MISCELLANEOUS, QC, Solar and Stellar Astrophysics (astro-ph.SR), QB, Physics, Earth and Planetary Astrophysics (astro-ph.EP), Photosphere, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrophysics - Solar and Stellar Astrophysics, [SDU]Sciences of the Universe [physics], ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Variable star, Astrophysics - Earth and Planetary Astrophysics
Abstract

We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <, 19 pages, 8 figures, accepted for publication in ApJL

Published
2018
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