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Full list of authors: De Marco, Orsola; Akashi, Muhammad; Akras, Stavros; Alcolea, Javier; Aleman, Isabel; Amram, Philippe; Balick, Bruce; De Beck, Elvire; Blackman, Eric G.; Boffin, Henri M. J.; Boumis, Panos; Bublitz, Jesse; Bucciarelli, Beatrice; Bujarrabal, Valentin; Cami, Jan; Chornay, Nicholas; Chu, You-Hua; Corradi, Romano L. M.; Frank, Adam; García-Hernández, D. A.; García-Rojas, Jorge; García-Segura, Guillermo; Gómez-Llanos, Veronica; Gonçalves, Denise R.; Guerrero, Martín A.; Jones, David; Karakas, Amanda I.; Kastner, Joel H.; Kwok, Sun; Lykou, Foteini; Manchado, Arturo; Matsuura, Mikako; McDonald, Iain; Miszalski, Brent; Mohamed, Shazrene S.; Monreal-Ibero, Ana; Monteiro, Hektor; Montez, Rodolfo; Baez, Paula Moraga; Morisset, Christophe; Nordhaus, Jason; Mendes de Oliveira, Claudia; Osborn, Zara; Otsuka, Masaaki; Parker, Quentin A.; Peeters, Els; Quint, Bruno C.; Quintana-Lacaci, Guillermo; Redman, Matt; Ruiter, Ashley J.; Sabin, Laurence; Sahai, Raghvendra; Contreras, Carmen Sánchez; Santander-García, Miguel; Seitenzahl, Ivo; Soker, Noam; Speck, Angela K.; Stanghellini, Letizia; Steffen, Wolfgang; Toalá, Jesús A.; Ueta, Toshiya; Van de Steene, Griet; Van Winckel, Hans; Ventura, Paolo; Villaver, Eva; Vlemmings, Wouter; Walsh, Jeremy R.; Wesson, Roger; Zijlstra, Albert A., Planetary nebulae—the ejected envelopes of red giant stars—provide us with a history of the last, mass-losing phases of 90% of stars initially more massive than the Sun. Here we analyse images of the planetary nebula NGC 3132 from the James Webb Space Telescope (JWST) Early Release Observations. A structured, extended hydrogen halo surrounding an ionized central bubble is imprinted with spiral structures, probably shaped by a low-mass companion orbiting the central star at about 40–60 au. The images also reveal a mid-infrared excess at the central star, interpreted as a dusty disk, which is indicative of an interaction with another closer companion. Including the previously known A-type visual companion, the progenitor of the NGC 3132 planetary nebula must have been at least a stellar quartet. The JWST images allow us to generate a model of the illumination, ionization and hydrodynamics of the molecular halo, demonstrating the power of JWST to investigate complex stellar outflows. Furthermore, new measurements of the A-type visual companion allow us to derive the value for the mass of the progenitor of a central star with excellent precision: 2.86 ± 0.06 M⊙. These results serve as pathfinders for future JWST observations of planetary nebulae, providing unique insight into fundamental astrophysical processes including colliding winds and binary star interactions, with implications for supernovae and gravitational-wave systems. © 2022, The Author(s), under exclusive licence to Springer Nature Limited., We acknowledge the International Astronomical Union that oversees the work of Commission H3 on Planetary Nebulae. It is through the coordinating activity of this committee that this paper came together. S.A. acknowledges support under the grant 5077 financed by IAASARS/NOA. J.A. and V.B. acknowledge support from the EVENTs/Nebulae-Web research programme, Spanish AEI grant PID2019-105203GB-C21. I.A. acknowledges the support of CAPES, Brazil (Finance Code 001). E.D.B. acknowledges financial support from the Swedish National Space Agency. E.G.B. acknowledges NSF grants AST-1813298 and PHY-2020249. J.C. and E.P. acknowledge support from an NSERC Discovery Grant. G.G.-S. thanks M. L. Norman and the Laboratory for Computational Astrophysics for the use of ZEUS-3D. D.A.G.-H. and A.M. acknowledge support from the ACIISI, Gobierno de Canarias and the European Regional Development Fund (ERDF) under grant with reference PROID2020010051 as well as from the State Research Agency (AEI) of the Spanish Ministry of Science and Innovation (MICINN) under grant PID2020-115758GB-I00. J.G.-R. acknowledges support from Spanish AEI under Severo Ochoa Centres of Excellence Programme 2020-2023 (CEX2019-000920-S). J.G.-R. and V.G.-L. acknowledge support from ACIISI and ERDF under grant ProID2021010074. D.R.G. acknowledges the CNPq grant 313016/2020-8. M.A.G. acknowledges support of grant PGC2018-102184-B-I00 of the Ministerio de Educación, Innovación y Universidades cofunded with FEDER funds and from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). D.J. acknowledges support from the Erasmus+ programme of the European Union under grant number 2020-1-CZ01-KA203-078200. A.I.K. and Z.O. were supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. This research is/was supported by an Australian Government Research Training Program (RTP) Scholarship. M.M. and R.W. acknowledge support from STFC Consolidated grant (2422911). C.M. acknowledges support from UNAM/DGAPA/PAPIIT under grant IN101220. S.S.M. acknowledges funding from UMiami, the South African National Research Foundation and the University of Cape Town VC2030 Future Leaders Award. J.N. acknowledges support from NSF grant AST-2009713. C.M.d.O. acknowledges funding from FAPESP through projects 2017/50277-0, 2019/11910-4 e 2019/26492-3 and CNPq, process number 309209/2019-6. J.H.K. and P.M.B. acknowledge support from NSF grant AST-2206033 and a NRAO Student Observing Support grant to Rochester Institute of Technology. M.O. was supported by JSPS Grants-in-Aid for Scientific Research(C) (JP19K03914 and 22K03675). Q.A.P. acknowledges support from the HKSAR Research grants council. Vera C. Rubin Observatory is a Federal project jointly funded by the National Science Foundation (NSF) and the Department of Energy (DOE) Office of Science, with early construction funding received from private donations through the LSST Corporation. The NSF-funded LSST (now Rubin Observatory) Project Office for construction was established as an operating centre under the management of the Association of Universities for Research in Astronomy (AURA). The DOE-funded effort to build the Rubin Observatory LSST Camera (LSSTCam) is managed by SLAC National Accelerator Laboratory (SLAC). A.J.R. was supported by the Australian Research Council through award number FT170100243. L.S. acknowledges support from PAPIIT UNAM grant IN110122. C.S.C.’s work is part of I+D+i project PID2019-105203GB-C22 funded by the Spanish MCIN/AEI/10.13039/501100011033. M.S.-G. acknowledges support by the Spanish Ministry of Science and Innovation (MICINN) through projects AxIN (grant AYA2016-78994-P) and EVENTs/Nebulae-Web (grant PID2019-105203GB-C21). R.S.’s contribution to the research described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. J.A.T. thanks the Marcos Moshisnky Fundation (Mexico) and UNAM PAPIIT project IA101622. E.V. acknowledges support from the ‘On the rocks II project’ funded by the Spanish Ministerio de Ciencia, Innovación y Universidades under grant PGC2018-101950-B-I00. A.A.Z. acknowledges support from STFC under grant ST/T000414/1. This research made use of Photutils, an Astropy package for detection and photometry of astronomical sources83, of the Spanish Virtual Observatory (https://svo.cab.inta-csic.es) project funded by MCIN/AEI/10.13039/501100011033/ through grant PID2020-112949GB-I00 and of the computing facilities available at the Laboratory of Computational Astrophysics of the Universidade Federal de Itajubá (LAC-UNIFEI, which is maintained with grants from CAPES, CNPq and FAPEMIG).

High-energy neutrinos are a promising tool for identifying astrophysical sources of high and ultra-high energy cosmic rays (UHECR). Prospects of detecting neutrinos at high energies ($\gtrsim$TeV) from blazars have been boosted after the recent association of IceCube-170922A and TXS 0506+056. We investigate the high-energy neutrino, IceCube-190331A, a high-energy starting event (HESE) with a high likelihood of being astrophysical in origin. We initiated a Swift/XRT and UVOT tiling mosaic of the neutrino localisation, and followed up with ATCA radio observations, compiling a multiwavelength SED for the most likely source of origin. NuSTAR observations of the neutrino location and a nearby X-ray source were also performed. We find two promising counterpart in the 90% confidence localisation region and identify the brightest as the most likely counterpart. However, no Fermi/LAT $\gamma$-ray source and no prompt Swift/BAT source is consistent with the neutrino event. At this point it is unclear whether any of the counterparts produced IceCube-190331A. We note that the Helix Nebula is also consistent with the position of the neutrino event, and we calculate that associated particle acceleration processes cannot produce the required energies to generate a high-energy HESE neutrino., Comment: 10 pages, 8 figures. Accepted for publication by MNRAS

Background: Many planetary nebulae retain significant quantities of molecular gas and dust despite their signature hostile radiation environments and energetic shocks. Photoionization and dissociation by extreme UV and (often) X-ray emission from their central stars drive the chemical processing of this material. Their well-defined geometries make planetary nebulae ideal testbeds for modeling the effects of radiation-driven heating and chemistry on molecular gas in photodissociation regions. Methods: We have carried out IRAM 30m/APEX 12m/ALMA radio studies of the Helix Nebula and its molecule-rich globules, exploiting the unique properties of the Helix to follow up our discovery of an anti-correlation between HNC/HCN line intensity ratio and central star UV Luminosity. Results: Analysis of HNC/HCN across the Helix Nebula reveals the line ratio increases with distance from the central star, and thus decreasing incident UV flux, indicative of the utility of the HNC/HCN ratio as a tracer of UV irradiation in photodissociation environments. However, modeling of the observed regions suggests HNC/HCN should decrease with greater distance, contrary to the observed trend. Conclusion: HNC/HCN acts as an effective tracer of UV irradiation of cold molecular gas. Further model studies are required.

Context. It has become clear in recent years that binarity plays a crucial role in many aspects of planetary nebulae (PNe), particularly with regard to the striking morphologies they exhibit. To date, there are nearly 60 known binary central stars of PNe (bCSPNe). However, both theory and observation indicate that this figure represents only the tip of the iceberg, with the Galactic PN population hosting orders of magnitude more stars. Aims. We are involved in a search for new bCSPNe with the aim of enhancing the statistical validation of the key role of binarity in the formation and shaping of PNe. New discoveries of bCSPNe and their characterization carry important implications not only for understanding PN evolution, but also for studying binary evolution and the common-envelope phase, which is still poorly understood. Methods. We used data from the TESS satellite to search for variability in the eight CSPNe that belong to the two-minute cadence of preselected targets in Cycle 1, with their available pipeline-extracted light curves. We identified strong periodicities and analysed them in the context of the binary scenario. Results. All the CSPNe but one (Abell 15) show clear signs of periodic variability in TESS. The cause of this variability can be attributed to different effects, some of them requiring the presence of a companion star. We find simple sinusoidal modulations in several of the systems, compatible with irradiation effects. In addition, two of the central stars (PG 1034+001 and NGC 5189) also show photometric variations due to ellipsoidal variations and other signs of variability that are probably caused by star spots or relativistic Doppler-beaming. The case of the well-studied Helix Nebula is of particular interest; here we constructed a series of binary models to explain the modulations we see in the light curve. We find that the variability constrains the possible companion to be very low-mass main-sequence star or sub-stellar object. We also identify, in substantial detail, the individual pulsation frequencies of NGC 246. © ESO 2020., Acknowledgements. We thank our anonymous referee for their useful comments that have improved the interpretation and discussion of the data. AA acknowledges support from Government of Comunidad Autónoma de Madrid (Spain) through postdoctoral Grant “Atracción de Talento Investigador” 2018-T2/TIC-11697. JLB and SBF acknowledge support from the Spanish State Research Agency (AEI) through projects No. ESP2017-87676-C5-1-R and No. MDM-2017-0737 Unidad de Excelencia “María de Maeztu” – Centro de Astrobiología (INTA-CSIC). DJ acknowledges support from the State Research Agency (AEI) of the Spanish Ministry of Science, Innovation and Universities (MCIU) and the European Regional Development Fund (FEDER) under grant AYA2017-83383-P. DJ also acknowledges support under grant P/308614 financed by funds transferred from the Spanish Ministry of Science, Innovation and Universities, charged to the General State Budgets and with funds transferred from the General Budgets of the Autonomous Community of the Canary Islands by the Ministry of Economy, Industry, Trade and Knowledge. LFM acknowledges partial support by grant AYA2017-84390-C2-1-R, co-funded with FEDER funds, and financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award for the Insti-tuto de Astrofísica de Andalucía (SEV-2017-0709). Authors are very grateful to Cristina Rodríguez López for guiding us with the analysis of RWT 152 and NGC 246. This research has made use of the SIMBAD database, operated at the CDS, Strasbourg (France), Aladin, NASA’s Astrophysics Data System Bibliographic Services, and the Spanish Virtual Observatory (http://svo.cab. inta-csic.es) supported from the Spanish MICINN/FEDER through grant AyA2017-84089. This publication makes use of data collected by TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program. We acknowledge the use of pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. This paper makes use of data products from the Mikulski Archive for Space Telescope.

We present and analyse 12CO, 13CO and C18O(2-1) ALMA observations of the C1 globule inside the Helix nebula in order to determine its physical properties. Our findings confirm the molecular nature of the globule with a multi-peak structure. The 12CO line has a high optical depth of about 10. The derived 12C/13C ratio of 10 and 16O/18O ratio of 115 are not in agreement with the expected isotopic ratios of carbon-rich AGB stars. Assuming that the 12CO optical depth has been underestimated, we can find a consistent fit for an initial mass of 2 Msol. We obtain a molecular mass of 2x10-4 Msol for the C1 globule, which is much higher than its mass in the literature. Clumping could play a role in the high molecular mass of the knot. The origin of the tail is discussed. Our findings show that the most probable model appears to be shadowing. The kinematics and molecular morphology of the knot are not consistent with a wind-swept model and the photoevaporation model alone is not enough to explain the nature of the globule. We propose an integrated model where the effects of the photoevaporation, the stream and shadowing models are all considered in the tail shaping process., 17 pages, 12 figures, accepted for publication in MNRAS

We present hydrostatic equilibrium models of spherical, self-gravitating clouds of helium and molecular hydrogen, focusing on the cold, high-density regime where solid- or liquid-hydrogen can form. The resulting structures have masses from 0.1 Msun down to several x 1.e-8 Msun, and span a broad range of radii: 1.e-4 < R(AU) < 1.e7. Our models are fully convective, but all have a two-zone character with the majority of the mass in a small, condensate-free core, surrounded by a colder envelope where phase equilibrium obtains. Convection in the envelope is unusual in that it is driven by a mean-molecular-weight inversion, rather than by an entropy gradient. In fact the entropy gradient is itself inverted, leading to the surprising result that envelope convection transports heat inwards. In turn that permits the outer layers to maintain steady state temperatures below the cosmic microwave background. Amongst our hydrostatic equilibria we identify thermal equilibria appropriate to the Galaxy, in which radiative cooling from H2 is balanced by cosmic-ray heating. These equilibria are all thermally unstable, albeit with very long thermal timescales in some cases. The specific luminosities of all our models are very low, and they therefore describe a type of baryonic dark matter. Consequently such clouds are thermally fragile: when placed in a harsh radiation field they will be unable to cool effectively and disruption will ensue as heat input drives a secular expansion. Disrupting clouds should leave trails of gas and H2 dust in their wake, which might make them easier to detect. Our models may be relevant to the cometary globules in the Helix Nebula, and the G2 cloud orbiting Sgr A*., 26 pages, 18 figures, ApJ (Accepted)

We study the development process of common resources in Helix Nebula. Helix Nebula is a meta-organization of highly heterogeneous collaborating actors, including scientific organizations like CERN,...

We report the detection of near-IR H$_2$ emission from the low-ionization structures (knots) in two planetary nebulae. The deepest ever, high-angular resolution H$_2$ 1-0 S(1) at 2.122$\mu$, H$_2$ 2-1 S(1) at 2.248$\mu$ and Br$\gamma$ images of K 4-47 and NGC 7662, obtained using the Near InfraRed Imager and Spectrometer (NIRI) at Gemini-North, are analyzed here. K 4-47 reveals a remarkable highly collimated bipolar structure not only in the optical but also in the molecular hydrogen emission. The H$_2$ emission emanates from the walls of the bipolar outflows and also from the pair of knots at the tip of the outflows. The H$_2$ 1-0 S(1)/2-1 S(1) line ratio ranges from ~7 to ~10 suggesting the presence of shock interactions. Our findings can be explained by the interaction of a jet/bullet ejected from the central star with the surrounding asymptotic giant branch material. The strongest H$_2$ line, v=1-0 S(1) is also detected in several low-ionization knots located at the periphery of the elliptical planetary nebula NGC 7662, but only four of these knots are detected in the H$_2$ v=2-1 S(1) line. These four knots exhibit an H$_2$ line ratio between 2 and 3.5, which suggests that the emission is caused by the UV ionizing flux of the central star. Our data confirms the presence of H$_2$ gas in both fast- and slow-moving low-ionization knots, which has only been confirmed before in the nearby Helix nebula and Hu 1-2. Overall, the low-ionization structures of planetary nebulae are found to share similar traits to photodissociation regions., Comment: 9 pages and 5 figures. MNRAS in press

While the population of main sequence debris discs is well constrained, little is known about debris discs around evolved stars. This paper provides a theoretical framework considering the effects of stellar evolution on debris discs, particularly the production and loss of dust within them. Here we repeat a steady state model fit to disc evolution statistics for main sequence A stars, this time using realistic grain optical properties, then evolve that population to consider its detectability at later epochs. Our model predicts that debris discs around giant stars are harder to detect than on the main sequence because radiation pressure is more effective at removing small dust around higher luminosity stars. Just 12% of first ascent giants within 100pc are predicted to have discs detectable with Herschel at 160um. However this is subject to the uncertain effect of sublimation on the disc, which we propose can thus be constrained with such observations. Our model also finds that the rapid decline in stellar luminosity results in only very young white dwarfs having luminous discs. As such systems are on average at larger distances they are hard to detect, but we predict that the stellar parameters most likely to yield a disc detection are a white dwarf at 200pc with cooling age of 0.1Myr, in line with observations of the Helix Nebula. Our model does not predict close-in (

Accepted: 2010-07-20, 資料番号: SA1002188000

Previous velocity images which reveal flows of ionized gas along the most prominent cometary tail (from Knot 38) in the Helix planetary nebula are compared with that taken at optical wavelengths with the Hubble Space Telescope and with an image in the emission from molecular hydrogen. The flows from the second most prominent tail from Knot 14 are also considered. The kinematics of the tail from the more complex Knot 32, shown here for the first time, also reveal an acceleration away from the central star. All of the tails are explained as accelerating ionized flows of ablated material driven by the previous, mildly supersonic, asymptotic giant branch wind from the central star. The longest tail of ionized gas, even though formed by this mechanism in a very clumpy medium, as revealed by the emission from molecular hydrogen, appears to be a coherent outflowing feature.

H2CO, c-C3H2, and C2H have been identified in the neutral envelope of the highly evolved planetary nebula (PN), the Helix (also know as NGC 7293). Emission from these species were detected toward a peak position in CO, 372'' east of the central star, using the facilities of the Arizona Radio Observatory (ARO). C2H and c-C3H2 were identified on the basis of their 3 mm transitions, measured with the ARO 12 m, while five lines of H2CO were observed using the 12 m at 2 and 3 mm and the ARO Submillimeter Telescope at 1 mm. From a radiative transfer analysis of the formaldehyde emission, the molecular material was determined to have a density of n(H2) ~3 × 105 cm–3, with a kinetic temperature of T kin ~20 K. Column densities for C2H, H2CO, and c-C3H2 of N tot ~1.4 × 1013 cm–2, 1.1 × 1012 cm–2, and 3 × 1011 cm–2, respectively, were derived, corresponding to fractional abundances relative to H2 of f (H2CO) = 1 × 10–7, f (c-C3H2) = 3 × 10–8, and f (C2H) = 1 × 10–6 . The physical conditions found support the notion that molecules in evolved PNe survive in dense clumps in pressure equilibrium, shielded from photodissociation. The presence of H2CO, c-C3H2, and C2H, along with the previously observed species CN, HNC, HCN, and HCO+, indicates that a relatively complex chemistry can occur in the late stages of PN evolution, despite potentially destructive ultraviolet radiation. These molecules have also been observed in diffuse clouds, suggesting a possible connection between molecular material in evolved PNe and the diffuse ISM.

We present a deep and wide field-of-view (4'x 7') image of the planetary nebula (PN) NGC 7293 (the Helix Nebula) in the 2.12 micron H2 v=1-0 S(1) line. The excellent seeing (0.4'') at the Subaru Telescope, allows the details of cometary knots to be examined. The knots are found at distances of 2.2'-6.4' from the central star (CS). At the inner edge and in the inner ring (up to 4.5' fromthe CS), the knot often show a `tadpole' shape, an elliptical head with a bright crescent inside and a long tail opposite to the CS. In detail, there are variations in the tadpole shapes, such as narrowing tails, widening tails, meandering tails, or multi-peaks within a tail. In the outer ring (4.5'-6.4' from the CS), the shapes are more fractured, and the tails do not collimate into a single direction. The transition in knot morphology from the inner edge to the outer ring is clearly seen. The number density of knots governs the H2 surface brightness in the inner ring: H2 exists only within the knots. Possible mechanisms which contribute to the shaping of the knots are discussed, including photo-ionization and streaming motions. A plausible interpretation of our images is that inner knots are being overrun by a faster wind, but that this has not (yet) reached the outer knots. Based on H2 formation and destruction rates, H2 gas can survive in knots from formation during the late asymptotic giant branch (AGB) phase throughout the PN phase. These observations provide new constraints on the formation and evolution of knots, and on the physics of molecular gas embedded within ionized gas.

Knots are commonly found in nearby planetary nebulae (PNe) and star forming regions. Within PNe, knots are often found to be associated with the brightest parts of the nebulae and understanding the physics involved in knots may reveal the processes dominating in PNe. As one of the closest PNe, the Helix Nebula (NGC 7293) is an ideal target to study such small-scale (~300 AU) structures. We have obtained infrared integral spectroscopy of a comet-shaped knot in the Helix Nebula using SINFONI on the Very Large Telescope at high spatial resolution (50-125 mas). With spatially resolved 2 micron spectra, we find that the H2 rotational temperature within the cometary knots is uniform. The rotational-vibrational temperature of the cometary knot (situated in the innermost region of the nebula, 2.5 arcmin away from the central star), is 1800 K, higher than the temperature seen in the outer regions (5-6 arcmin from the central star) of the nebula (900 K), showing that the excitation temperature varies across the nebula. The obtained intensities are reasonably well fitted with 27 km s-1 C-type shock model. This ambient gas velocity is slightly higher than the observed [HeII] wind velocity of 13 km s-1. The gas excitation can also be reproduced with a PDR (photo dominant region) model, but this requires an order of magnitude higher UV radiation. Both models have limitations, highlighting the need for models that treats both hydrodynamical physics and the PDR., Comment: Accepted for publication in MNRAS; A pdf file with full resolution images is available from http://optik2.mtk.nao.ac.jp/~mikako/abstract/helix.pdf

Excess emission from a point-like source coincident with the central star of the Helix Nebula is detected with Spitzer at 8, 24, and 70 um. At 24 um, the central source is superposed on an extended diffuse emission region. While the [OIV] 25.89 um line contributes to the diffuse emission, a 10-35 um spectrum of the central source shows a strong thermal continuum. The excess emission from the star most likely originates from a dust disk with blackbody temperatures of 90--130 K. Assuming a simple optically thin debris disk model, the dust is distributed in a ring between ~35 and ~150 AU from the central star, possibly arising from collisions of Kuiper-Belt-like Objects or the break-up of comets from an Oort-like cloud that have survived from the post-main-sequence evolution of the central star., Comment: emulateapj format, accepted for publication in ApJ Letters

We have examined a stream-source model for the production of the cometary tails observed in the Helix Nebula NGC 7293 in which a transonic or moderately supersonic stream of ionized gas overruns a source of ionized gas. Hydrodynamic calculations reveal velocity structures which are in good agreement with the observational data on tail velocities and are consistent with observations of the nebular structure. The results also are indicative of a stellar atmosphere origin for the cometary globules. Tail remnants persist for timescales long enough for their identification with faint striations visible in the nebula gas to be plausible., Comment: 7 pages, 6 figures, accepted for publication in A&A

On the basis that the cometary knots observed in the Helix Nebula form as a result of larger parent clouds breaking up due to Rayleigh-Taylor instability induced by radiative acceleration of the clouds, we compute characteristics of the cometary knots and of the parent clouds as well. Present observations place constraints on the positions, velocities, and sizes of the parent clouds. Requiring the clouds to produce cometary knots that are stable places further constraints on the properties of parent clouds. We formulate those constraints and show how they further limit the predicted properties of the cometary knots and bring them into agreement with their observed properties.

We present HST/NICMOS imaging of the H_2 2.12 \mu m emission in 5 fields in the Helix Nebula ranging in radial distance from 250-450" from the central star. The images reveal arcuate structures with their apexes pointing towards the central star. Comparison of these images with comparable resolution ground based images reveals that the molecular gas is more highly clumped than the ionized gas line tracers. From our images, we determine an average number density of knots in the molecular gas ranging from 162 knots/arcmin^2 in the denser regions to 18 knots/arcmin^2 in the lower density outer regions. Using this new number density, we estimate that the total number of knots in the Helix to be ~23,000 which is a factor of 6.5 larger than previous estimates. The total neutral gas mass in the Helix is 0.35 M_\odot assuming a mass of \~1.5x10^{-5} M_\odot for the individual knots. The H_2 intensity, 5-9x10^{-5} erg s^{-1} cm^{-2} sr^{-1}, remains relatively constant with projected distance from the central star suggesting a heating mechanism for the molecular gas that is distributed almost uniformly in the knots throughout the nebula. The temperature and H_2 2.12 \mu m intensity of the knots can be approximately explained by photodissociation regions (PDRs) in the individual knots; however, theoretical PDR models of PN under-predict the intensities of some knots by a factor of 10., Comment: 26 pages, 3 tables, 10 figures; AJ accepted

Through HST imaging of the inner part of the main-ring of the Helix Nebula together with CTIO 4-m images of the fainter outer parts, we have an unprecedented-quality view of the nearest bright planetary nebula. These images have allowed determination that the main-ring of the nebula is composed of an inner-disk of about 499\arcsec diameter (0.52 pc) surrounded by an outer-ring (in reality a torus) of 742\arcsec diameter (0.77 pc) whose plane is highly inclined to the plane of the disk. This outer-ring is surrounded by an outermost-ring of 1500\arcsec (1.76 pc) diameter which is flattened on the side colliding with the ambient interstellar medium. The inner-disk has an extended distribution of low density gas along its rotational axis of symmetry and the disk is optically thick to ionizing radiation, as is the outer-ring. Published radial velocities of the knots provides support for the two-component structure of the main-ring of the nebula and to the idea that the knots found there are expanding along with the nebular material from which it recently originated. There is a change in the morphology of the knots as a function of the distance from the local ionization front. This supports a scenario in which the knots are formed in or near the ionization front and are then sculpted by the stellar radiation from the central star as the ionization front advances beyond them., 30 pages, 20 figures, many figures have reduce fidelity for astroph preprint. Note: URLs in preprint were changed

I present and illustrate some of the most recent HST results and the plans for future observations, including the current studies of solar system planets, the extensive imaging of the Helix Nebula, the detection of superluminally expanding light echoes around the newly discovered variable star V838 Mon, the repeated measurements of the collision of SN 1987A ejecta with its inner circumstellar ring, that show a marked increase of high energy interactions, the study of M31 halo stellar populations and the puzzle of their origin, and the plans for the ACS Ultra-Deep Field observations that will probe the Universe to an unprecedented depth.

We present a 065 resolution H2 1-0 S(1) 2.122 μm image of the Ring Nebula (NGC 6720), which was taken with the Near Infrared Imager at the WIYN 3.5 m telescope on Kitt Peak. The high resolution of the H2 observation is sufficient to reveal the finer structure of the molecular material in this nebula. The morphology of the molecular emission is compared to that of the ionized emission from the Ring Nebula as seen by the Hubble Space Telescope (HST; He ii, [O iii], and [N ii]), and it is clear that the dark clumps seen by HST match the locations of clumpy H2 emission, suggesting that these clumps are similar to the cometary knots seen in the Helix Nebula. As with the Helix, the clumpy H2 emission from the main ring of the Ring Nebula is contained within the optically bright ionized nebula, implying that the molecular gas is shielded inside dense condensations. Comparison of the observed H2 average surface brightnesses for the Ring Nebula [(1.5 ± 0.5) × 10-4 ergs cm–2 s–1 sr–1] with time-dependent models of the expected H2 emission from planetary nebulae (PNe) shows that it is consistent with H2 excitation in photodissociation regions (PDRs), confirming previous suggestions. Comparison of the Ring Nebula H2 emission with a younger PN, NGC 2346, and an older PN, the Helix Nebula, suggests an evolution in H2 surface brightness consistent with the time-dependent PDR models. Moreover, the knots of molecular gas appear to become more isolated as the PN evolves, consistent with optical studies of knots in PNe.

[Aims] In our series of papers presenting the Herschel imaging of evolved planetary nebulae, we present images of the dust distribution in the Helix nebula (NGC 7293)., [Methods] Images at 70, 160, 250, 350, and 500 μm were obtained with the PACS and SPIRE instruments on board the Herschel satellite., [Results] The broadband maps show the dust distribution over the main Helix nebula to be clumpy and predominantly present in the barrel wall. We determined the spectral energy distribution of the main nebula in a consistent way using Herschel, IRAS, and Planck flux values. The emissivity index of β = 0.99 ± 0.09, in combination with the carbon rich molecular chemistry of the nebula, indicates that the dust consists mainly of amorphous carbon. The dust excess emission from the central star disk is detected at 70 μm and the flux measurement agrees with previous measurement. We present the temperature and dust column density maps. The total dust mass across the Helix nebula (without its halo) is determined to be 3.5 × 10-3 M⊙ at a distance of 216 pc. The temperature map shows dust temperatures between 22 K and 42 K, which is similar to the kinetic temperature of the molecular gas, confirming that the dust and gas co-exist in high density clumps. Archived images are used to compare the location of the dust emission in the far infrared (Herschel) with the ionized (GALEX and Hβ) and molecular (H2) component. The different emission components are consistent with the Helix consisting of a thick walled barrel-like structure inclined to the line of sight. The radiation field decreases rapidly through the barrel wall., This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT/MCYT (Spain). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC (UK); and NASA (USA). Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. P.v.H. and the PACS ICC in Leuven wish to acknowledge support from the Belgian Science Policy office through the ESA PRODEX programme. M.E., J.R.G. and J.C. thank the Spanish MINECO for funding support from grants CSD2009-00038, AYA2009-07304 and AYA2012-32032.

L.C. thanks the Spanish MICINN for funding support through grants AYA2009-07304 and CSD2009-00038, Arnaud, M., Atrio-Barandela, F., Aumont, J., Baccigalupi, C., Banday, A.J., Barreiro, R.B., Battaner, E., Benabed, K., Benoit-Lévy, A., Bernard, J.-P., Bersanelli, M., Bielewicz, P., Bonaldi, A., Bond, J.R., Borrill, J., Bouchet, F.R., Buemi, C.S., Burigana, C., Cardoso, J.-F., Casassus, S., Catalano, A., Cerrigone, L., Chamballu, A., Chiang, H.C., Colombi, S., Colombo, L.P.L., Couchot, F., Crill, B.P., Curto, A., Cuttaia, F., Davies, R.D., Davis, R.J., De Bernardis, P., De Rosa, A., De Zotti, G., Delabrouille, J., Dickinson, C., Diego, J.M., Donzelli, S., Doré, O., Dupac, X., Enßlin, T.A., Eriksen, H.K., Finelli, F., Frailis, M., Franceschi, E., Galeotta, S., Ganga, K., Giard, M., González-Nuevo, J., Górski, K.M., Gregorio, A., Gruppuso, A., Hansen, F.K., Harrison, D.L., Hildebrandt, S.R., Hivon, E., Holmes, W.A., Hora, J.L., Hornstrup, A., Hovest, W., Huffenberger, K.M., Jaffe, T.R., Jones, W.C., Juvela, M., Keihänen, E., Keskitalo, R., Kisner, T.S., Knoche, J., Kunz, M., Kurki-Suonio, H., Lähteenmäki, A., Lamarre, J.-M., Lasenby, A., Lawrence, C.R., Leonardi, R., Leto, P., Lilje, P.B., Linden-Vørnle, M., López-Caniego, M., Macías-Pérez, J.F., Maffei, B., Maino, D., Mandolesi, N., Martin, P.G., Masi, S., Massardi, M., Matarrese, S., Mazzotta, P., Mendes, L., Mennella, A., Migliaccio, M., Miville-Deschênes, M.-A., Moneti, A., Montier, L., Morgante, G., Mortlock, D., Munshi, D., Murphy, J.A., Naselsky, P., Nati, F., Natoli, P., Noviello, F., Novikov, D., Novikov, I., Pagano, L., Pajot, F., Paladini, R., Paoletti, D., Peel, M., Perdereau, O., Perrotta, F., Piacentini, F., Piat, M., Pietrobon, D., Plaszczynski, S., Pointecouteau, E., Polenta, G., Popa, L., Pratt, G.W., Procopio, P., Prunet, S., Puget, J.-L., Rachen, J.P., Reinecke, M., Remazeilles, M., Ricciardi, S., Riller, T., Ristorcelli, I., Rocha, G., Rosset, C., Roudier, G., Rubiño-Martín, J.A., Rusholme, B., Sandri, M., Savini, G., Scott, D., Spencer, L.D., Stolyarov, V., Sutton, D., Suur-Uski, A.-S., Sygnet, J.-F., Tauber, J.A., Terenzi, L., Toffolatti, L., Tomasi, M., Trigilio, C., Tristram, M., Trombetti, T., Tucci, M., Umana, G., Valiviita, J., Van Tent, B., Vielva, P., Villa, F., Wade, L.A., Wandelt, B.D., Zacchei, A., Zijlstra, A., Zonca, A.

We analyze the small scale structure in the circumstellar envelopes of NGC 7027 and IRC+10216, using high resolution optical images in dust scattered light. We use the observations to test the proposal that globules in planetary nebulae, typified by globules in the Helix nebula, originate in high density contrast proto-globules in the atmosphere of the progenitor AGB star and are carried out in the circumstellar wind (Dyson et al. 1989). We find no evidence for the presence of proto- globules in the extended envelopes of NGC 7027 and IRC+10216 with the expected sizes and masses>10 5 M which are needed to produce globules like those in the Helix nebula. We do find azimuthal structure in the envelopes on size scales of l> 0:1d where d is the radial distance, consistent with the smoothing out of small scale structure by thermal motions in the wind acceleration region. Unless globules require special conditions not found in NGC 7027 or IRC+10216, which are among the most likely precursors of Helix-like nebulae, our results argue against their origin in the atmosphere of the central star. We suggest alternative scenarios for globule formation, including the fragmentation of the neutral circumstellar gas at the transition phase by directed outflows or jets.

HST emission-line images of five of the arguably closest planetary nebulae have shown that there is a progression of characteristics of their knots. This progression begins with dark tangential structures showing no alignment with the central star and location near the main ionization front. At the end of the progression in the largest nebulae, the knots are located throughout much of the ionized zone, where they are photoionized on the side facing the central star and accompanied by long tails well aligned radially. This modification of characteristics is what would be expected if the knots were formed near or outside the main ionization front, obtaining densities high enough to lead to their being only partially ionized as they are fully illuminated by the Lyman continuum (Lyc) radiation field. Their expansion velocities must be lower than that of the main body of the nebular shell. Their forms are altered by exposure to the radiation field from the star, although it is not clear as to the relative role of radiation pressure acting on the dust component vis-a-vis ionization shadowing. The one object that does not fit into this sequence is NGC 2392, which is the most complex nebula in our sample. In this case the inner part of the nebula is composed of a series of loops of material, some being ionization bounded, which cover only a small fraction of the area illuminated by the star. This complex structure may be what gives rise to the large variations in electron temperature inferred from low spatial resolution observations. Cometary-form knots are seen in the outer part of this object, with these objects closely resembling those found in the largest nebula in our sample, NGC 7293.

We present new observations of the ionized gas, molecular gas, and cool dust in the Helix Nebula (NGC 7293). The ionized gas is observed in the form of an Himage, which is constructed using images from the Southern HSky Survey Atlas. The molecular emission was mapped using the H2 v =1 ! 0 S(1) line at 2.122 lm. The far-infrared (FIR) observations were obtained using ISOPHOT on the Infrared Space Observ- atory. The Hobservations are more sensitive than previous measurements and show the huge extent of the Helix, confirming it as a density-bounded nebula and showing previously unseen point-symmetric structures. The H2 observations show that the molecular gas follows the distribution of molecular material shown in pre- vious work. The molecular emission is confined to that part of the nebula seen in the classic optical image. Furthermore, comparison of the H2 emission strength with time-dependent models for photodissociation regions (PDRs) shows that the emission arises from thermal excitation of the hydrogen molecules in PDRs and not from shocks. The FIR observations, at 90 and 160 lm, represent mostly contributions from thermal dust emission from cool dust grains but include a small contribution from ionized atomic lines. Comparison of the FIR emission with the Hobservation shows that the dust and ionized gas are coincident and extend to � 1100 00 radius. This equates to a spatial radial extent of more than 1 pc (assuming a distance to the Helix of � 200 pc). Assuming that the outer layers of the circumstellar shell have spherical symmetry, radiative transfer modeling of the emission in Hgives a shell mass of � 1.5 M� . However, the modeling does not cover the outermost part of the shell (beyond � 600 00 radius), and therefore this is a lower limit for the shell mass. Moreover, the models suggest the need for very large dust grains, with � 80% of the dust mass in grains larger than 3.5 lm. Comparison of these new observations with previous observations shows the large-scale stratifi- cation of the Helix in terms of ionized gas and dust, as well as the coexistence of molecular species inside the ionized zones, where molecules survive in dense condensations and cometary knots.

Several lines of observational evidence suggest that white dwarfs receive small birth kicks due to anisotropic mass loss. If other stars possess extrasolar analogues to the Solar Oort cloud, the orbits of comets in such clouds will be scrambled by white dwarf natal kicks. Although most comets will be unbound, some will be placed on low angular momentum orbits vulnerable to sublimation or tidal disruption. The dusty debris from these comets will manifest itself as an IR excess temporarily visible around newborn white dwarfs; examples of such disks may already have been seen in the Helix Nebula, and around several other young white dwarfs. Future observations with the James Webb Space Telescope may distinguish this hypothesis from alternatives such as a dynamically excited Kuiper Belt analogue. Although competing hypotheses exist, the observation that $\gtrsim 15\%$ of young white dwarfs possess such disks, if interpreted as indeed being cometary in origin, provides indirect evidence that low mass gas giants (thought necessary to produce an Oort cloud) are common in the outer regions of extrasolar planetary systems. Hydrogen abundances in the atmospheres of older white dwarfs can, if sufficiently low, also be used to place constraints on the joint parameter space of natal kicks and exo-Oort cloud models., 22 pages, 13 figures, published in MNRAS. Changes made to match published version

We compare the morphology of the cometary knots in the Helix Nebula in different emission lines using Hubble Space Telescope Wide Field Planetary Camera 2 and Space Telescope Imaging Spectrograph observations. We find that the [N II] 6658 A line emission from the cometary heads is displaced with respect to Hα, peaking at a position that is closer to the central ionizing star. This result seems at first sight to be in conflict with simple photoionization models, which predict that the [N II] emission is closer to the ionization front (IF) because it is confined to a thin H+-He0 layer, a prediction confirmed by calculations with both our own and the CLOUDY programs. However, the ratio of [N II] to Hα is very temperature sensitive, and the observations can be explained if the knots are modeled as photoevaporating globules. In this case, there is a strong temperature gradient across the IF, resulting in the [N II] emission being depressed in the partially neutral zones. We also find a strong correlation between the strength of the [N II] and [O III] emission in individual knots, with both being higher in the knots that are closer to the central star. On the current evidence, it is unclear whether this is due to interknot variations in metal abundances or in gas temperature.

Linear features of up to 0.25 pc length are seen in both the Helix Nebula and the Orion Nebula. These features are most evident in emission-line ratio images. It is demonstrated that in both objects the features are along projections of lines between the dominant star and an optically thick compact feature (the cometary knots in the Helix and the proplyds in Orion). In general, these features are caused by shadowing of Lyman continuum radiation from the photoionizing star, although in the case of the Helix features, extinction by entrained dust plays a role. Some of the rays have neutral hydrogen cores. It is shown that the characteristics of these linear features can be used to analyze the three-dimensional structure of the nebulae. If the most recent model for these rays is correct and the electron temperature of the shadowed gas is only two-thirds that of the ambient material, then these rays play a small but measurable role in solving the t2 problem.

We have obtained deep optical spectra of the planetary nebula NGC 6153, both along its minor axis and by uniformly scanning a long slit across the whole nebula. The scanned spectra, when combined with the nebular total H beta flux, yield integrated fluxes for all the lines (similar to 400) in our spectra, which are rich in strong recombination lines from C, N, O and Ne ions. A weak O vi lambda 3811 emission line from the central star has been detected, suggesting that the nucleus of NGC 6153 has a hydrogen-deficient surface. The optical data, together with the ISO LWS 43-197 mu m spectrum and the archival IUE and IRAS LRS spectra, are used to study the thermal and density structure and to derive the heavy-element abundances from lines produced by different excitation mechanisms. In all cases, the C2+/H+, N2+/H+, O2+/H+ and Ne2+/H+ abundances derived from multiple optical recombination lines (ORLs) are consistently higher, by about a factor of 10, than the corresponding values deduced from optical, UV or infrared (IR) collisionally excited lines (CELs), regardless of the excitation energies or critical densities of the latter. The agreement between the temperature-sensitive optical forbidden lines and the temperature-insensitive IR fine-structure lines rules out temperature fluctuations as the cause of the large difference between the ORL and CEL abundances.We present the results of a new calculation of recombination coefficients for [O II] which lead to good agreement between the observed and predicted [O II] lambda lambda 7320, 7330 forbidden line intensities if these lines are solely excited by recombination at the Balmer jump temperature. Recombination excitation is also found to be important in exciting the [N ii] lambda 5754 line, which, if unaccounted for, would lead to an overestimated [N ii] temperature from the observed (lambda 6548+lambda 6584)/lambda 5754 ratio. Analysis of a number of C ii lines arising from levels as high as 7g in the recombination ladder reveals excellent agreement between their reddening-corrected relative intensities and those predicted by recombination theory. Spatial analysis of the long-slit spectra taken along the nebular minor axis yields a varying [O iii] temperature, whereas the hydrogen Balmer jump temperature of 6000 K is approximately constant across the nebula, and is 2000-3000 K lower than the [O iii] temperature. The observed high-n Balmer line decrement indicates that the hydrogen lines arise from material having an electron density of 2000(-1000)(+2000) cm(-3), consistent with the optical and IR forbidden-line density diagnostics, which yield average line-of-sight electron densities along the minor axis varying between 2000 and 4000 cm(-3).While the He/H ratio mapped by He I and He ii recombination lines is constant within 5 per cent across the nebula, the C2+/H+ and O2+/H+ recombination-line abundances decrease by a factor of 2-3 over a radius of 15 arcsec from the centre, pointing to the presence of abundance gradients. We consider a variety of hypotheses to account for the observed behaviour of the various thermal, density and abundance diagnostics. Empirical nebular models containing two components with differing densities and temperatures are able to account for many of the observed patterns, but only if one of the components is significantly hydrogen-deficient. One such model, which gives a good fit to the observed line intensities and patterns, has 500-K H-depleted material, presumed to be evaporating from dense neutral inclusions, embedded in 9500-K material with 'normal' abundances. An alternative model, which appears more physically plausible on a number of grounds, has high-density (2x10(6) cm(-3)), fully ionized, H-deficient knots embedded in the 'normal' component, although this model fails to account adequately for the observed low (6000 K) hydrogen Balmer jump temperature. However, the observed fact that the ORLs and CELs yield heavy-element abundance ratios that are identical within the uncertainties finds no obvious explanation in the context of H-deficient knot models.

We present a fully sampled map of the Helix Nebula in the 1.3 mm CO J = 2-1 line, made using the Caltech Submillimeter Observatory. The angular resolution is 31'', and the velocity resolution is 1.5 km s-1. The CO emission is found to extend over a region ~1000'' × 800'' and delineates the well-known double ring or "helix" seen in optical images of the ionized gas. Our observations provide the first complete view of the global kinematics of the envelope and reveal the three-dimensional structure of the gas. The helix is seen to be an expanding, equatorial ring around the ionized nebula, with arcs extending to higher latitudes and exhibiting remarkable point symmetries about the central star. The molecular gas is fragmented into many small condensations with narrow line widths (~1 km s-1). The close relationship found between the structure of the envelope and the ionized nebula underscores the important role of neutral gas in determining the morphology of planetary nebulae. The point symmetries provide evidence for early shaping of the envelope by bipolar outflows or jets.

We present new, infrared and millimeter views of the Helix nebula which illustrate the critical role of remnant, neutral AGB envelopes in the formation and evolution of planetary nebulae. Large scale ∼ 1 000″ mapping of the entire nebula in the CO (J = 2 − 1) line with the CSO reveals the global structure of the envelope. The CO emission forms the familiar ring structure seen in optical images of the Helix, and indicates a massive remnant with ≳ 50% the mass of the ionized nebula. High resolution CO mapping with the IRAM 30 m telescope shows that the whole envelope is fragmented into an intricate array of small clumps, closely related to the cometary globules seen in the central, ionized cavity. 5–17 μm spectroscopy of the Helix with ISOCAM reveals a remarkable near infrared spectrum, dominated by the pure (v = 0 − 0) rotational lines of H2. The H2 lines are excited to a temperature of ∼ 900 K, and likely arise in warm, outer layers of the small clumps seen in CO. Imaging of the H2 emission with ISOCAM over the whole nebula provides a striking portrait of the fragmented neutral envelope. 3-dimensional views of the envelope are also presented, based on CO mapping and using 3-dimensional visualization techniques. Point symmetries dominate the toroidal structure, and suggest an origin for the Helix in equatorial mass-loss on the AGB, shaped by the action of bipolar outflows or jets.

The structure and conditions within the Helix Nebula have been determined from emission-line images in Hβ, [O III], and He II and using spectra tracing a radial from the central star almost out to the northern boundary of the optical object. The nebula is approximately like a thick disk, rather than the torus suggested by low-ionization ions. The central region, previously thought to be a cavity, is filled with He+2 with a total gas density comparable to the main ring. The electron temperature in the outer part was determined from [N II] line ratios to be 9400 ± 200 K, while [O III] lines gave 11700 ± 700 K for the bulk of the main ring of intermediate-ionization material. The Hα/Hβ ratio is anomalously low in the central portion, suggesting that the electron temperature there is very high. The likely source of this elevated central temperature is heating by photoelectric electrons from grains mixed in with the nebular gas, since this process depends directly on the distance from the central star and becomes relatively more important than photoionization heating at the low nebular densities that apply for the helix. However, it is unlikely that the two-phase condition that can exist when photoelectric heating dominates has produced the cometary knots that freely populate this nearby planetary nebula.

The Hα surface brightness distribution of cometary knots in the Helix Nebula is investigated. The brightness profiles of their photoionized surfaces (cusps) drop exponentially with increasing distance r from the center of the knots: Σ(r) ~ exp (-r/h). An r-3 profile, which would be expected for a freely expanding ionization region, in general does not provide a good fit. The cusps of all the knots have the same universal exponential brightness scale height h of 2 pixels (6.3 × 1014 cm), which is also independent of the direction with respect to the central star. The origin of the cometary knots and the formation and nature of their luminous cusps is investigated. We propose that the cusps are in hydrostatic equilibrium rather than freely expanding, but we have been unable to identify a physical mechanism that will constrain them. Lyα radiation pressure acting on the dust is evaluated as a mechanism to do the confinement, but it lacks sufficient energy density, and the scale height expected disagrees with what is observed.

Shadows behind neutral clumps in photoionized regions can have a neutral core surrounded by gas that is photoionized by the diffuse flux produced by the nebula. We present a simple analytic model describing the configuration of such shadows. We also present numerical gasdynamic simulations of the relaxation to the final, steady state. These models have clear applications (e.g., to the cometary knots in the Helix Nebula) but can also be applied in other astrophysical contexts.

We report infrared images of the Helix Nebula centered at 6.9 ?m (LW2 filter) and 15 ?m (LW3 filter) obtained with ISOCAM on board the Infrared Space Observatory (ISO). Three fields were also measured using the ISOCAM circular variable filter (CVF). The CVF data show that the 5-16.6 ?m spectrum is dominated by the pure (v=0-0) rotational lines of molecular hydrogen from the S(7) to the S(2) transitions. The strong S(5) H2 line accounts for most of the emission detected in the LW2 filter. The only atomic lines detected are [Ne II] 12.81 ?m and [Ar III] 8.99 ?m, which are weak, and [Ne III] 15.55 ?m, which is strong and accounts for most of the emission in the LW3 filter. No emission bands or continuum of small dust particles are detected despite the carbon richness of the Helix Nebula. The H2 emission traces the individual cometary globules of the molecular envelope of the nebula, whereas the [Ne III] emission is distributed along this envelope toward the inner regions of the ionized cavity. The intensities of H2 rotational lines are accurately predicted using a rotational temperature of 900?50 K and column densities of ~3?10 -->18 cm-2. The total luminosity in the H2 lines ~4 L? (6% of the star luminosity) is much higher than predicted for photodissociation regions. The significant absence of mid-infrared dust features indicates that in this evolved planetary nebula, the molecular-sized dust particles might have been destroyed by the exposure to the radiation field from the central hot star.

The system of cometary knots in the Helix planetary nebula (NGC 7293) has been systematically observed using ground-based images and long-slit, high-resolution spectroscopy. CCD images in the [N ii] 6584-A line, taken with the ESO NTT, are used to determine the spatial distribution of the knots; images in the [O iii] 5007-A line distinguish their position within the nebula on the basis of the absorption of the central [O iii] 5007-A-emitting zone of the Helix nebula. The kinematics of 50 of the brighter knots and their tails were studied primarily with the Manchester Echelle Spectrograph (MES) as well as the ESO NTT using the EMMI spectrograph. Three regions were covered by multiple exposures of a 10-element multislit with MES to obtain [N ii] 6584-A line profiles along 300 individual slit positions. In addition, many long-slit MES spectra, placed diametrically across the nebula, were obtained to compare the kinematics of the knots with the large-scale kinematical structure of the nebula. The global expansion of the system of knots is around 14 km s−1, some 17 km s−1 less than for the overrunning gas, and they are distributed in a thick central disc. The velocity field of the system of knots is similar to that of molecular (CO) emission but with a lower expansion velocity. Most knots are external to the central [O iii] 5007-A-emitting region, but some still show localized [O iii] 5007-A emission from their heads. The kinematical structure of two of the latter knots as revealed by profiles of the [O i] 6300-A, [N ii] 6584-A, [O iii] 5007-A and Hα emission lines is considered in detail and compared with their CO emission-line profiles. The interstellar absorption by the core of a further knot is derived from an [O iii] 5007-AHST image combined with MES [O iii] 5007-A profiles. Accurate masses, densities and ages are determined as a consequence. Furthermore, a kinematical model shows that the [N ii] 6584-A-emitting flow around a dusty, molecular globule (the core of an ionized knot) arises mainly from the expanding ionized gas of the Helix nebula engulfing the knot. The flow, parallel to the globule's photoionized surface, is mildly supersonic. The relationship between the system of knots and the large-scale structure is discussed.

The magnetic field in the central few hundred parsecs of the Milky Way has a dipolar geometry and is substantially stronger than elsewhere in the Galaxy, with estimates ranging up to a milligauss (refs 1-6). Characterization of the magnetic field at the Galactic Centre is important because it can affect the orbits of molecular clouds by exerting a drag on them, inhibit star formation, and could guide a wind of hot gas or cosmic rays away from the central region. Here we report observations of an infrared nebula having the morphology of an intertwined double helix about 100 parsecs from the Galaxy's dynamical centre, with its axis oriented perpendicular to the Galactic plane. The observed segment is about 25 parsecs in length, and contains about 1.25 full turns of each of the two continuous, helically wound strands. We interpret this feature as a torsional Alfvén wave propagating vertically away from the Galactic disk, driven by rotation of the magnetized circumnuclear gas disk. The direct connection between the circumnuclear disk and the double helix is ambiguous, but the images show a possible meandering channel that warrants further investigation.

著者人数: 16名, Accepted: 2014-03-28, 資料番号: SA1140078000

We have discovered two molecular features at radial velocities of -35 km/s and 0 km/s toward the infrared Double Helix Nebula (DHN) in the Galactic center with NANTEN2. The two features show good spatial correspondence with the DHN. We have also found two elongated molecular ridges at these two velocities distributed vertically to the Galactic plane over 0.8 degree. The two ridges are linked by broad features in velocity and are likely connected physically with each other. The ratio between the 12CO J=2-1 and J=1-0 transitions is 0.8 in the ridges which is larger than the average value 0.5 in the foreground gas, suggesting the two ridges are in the Galactic center. An examination of the K band extinction reveals a good coincidence with the CO 0 km/s ridge and is consistent with a distance of 8 +/-2 kpc. We discuss the possibility that the DHN was created by a magnetic phenomenon incorporating torsional Alfv��n waves launched from the circumnuclear disk (Morris, Uchida & Do 2006) and present a first estimate of the mass and energy involved in the DHN., 32 pages, 23 figures, Accepted by ApJ

The recent paradigm shift toward cloud computing in IT, and general interest in "Big Data" in particular, have demonstrated that the computing requirements of HEP are no longer globally unique. Indeed, the CERN IT department and LHC experiments have already made significant R&D; investments in delivering and exploiting cloud computing resources. While a number of technical evaluations of interesting commercial offerings from global IT enterprises have been performed by various physics labs, further technical, security, sociological, and legal issues need to be address before their large-scale adoption by the research community can be envisaged. Helix Nebula - the Science Cloud is an initiative that explores these questions by joining the forces of three European research institutes (CERN, ESA and EMBL) with leading European commercial IT enterprises. The goals of Helix Nebula are to establish a cloud platform federating multiple commercial cloud providers, along with new business models, which can sustain the cloud marketplace for years to come. This contribution will summarize the participation of CERN in Helix Nebula. We will explain CERN's flagship use-case and the model used to integrate several cloud providers with an LHC experiment's workload management system. During the first proof of concept, this project contributed over 40.000 CPU-days of Monte Carlo production throughput to the ATLAS experiment with marginal manpower required. CERN's experience, together with that of ESA and EMBL, is providing a great insight into the cloud computing industry and highlighted several challenges that are being tackled in order to ease the export of the scientific workloads to the cloud environments.

The nature and origin of the hundreds of ionized knots, with cometary tails, in the Helix planetary nebula are both being unravelled by recent observations. Healey and Huggins (1990, AJ, 100, 511), Meaburn et al (1992, MNRAS, 255, 177) and Walsh and Meaburn (1993, ESO Messenger, 73, 35) all showed, in various ways, that these knots have dense (106 cm–3), dusty, molecular cores with ionized arcs of gas on the surfaces pointing towards the ionizing star. This structure is confirmed in detail by the HST imagery of O'Dell and Handron (1996, ApJ, in press).

The observational status of the polarisation of the anomalous microwave emission (AME) is reviewed, both for individual compact Galactic regions as well as for the large-scale Galactic emission. There are six Galactic regions with existing polarisation constraints in the relevant range of 10–40 GHz: four dust clouds (Perseus,ρOphiuchi, LDN1622, and Pleiades) and two HII regions (LPH96 and the Helix nebula). These constraints are discussed in detail and are complemented by deriving upper limits on the polarisation of the AME for those objects without published WMAP constraints. For the case of large-scale emission, two recent works, based on WMAP data, are reviewed. Currently, the best constraints on the fractional polarisation of the AME, at frequencies near the peak of the emission (i.e., 20–30 GHz), are at the level of~1% (95.4% confidence level). Finally, we compare these constraints with the predictions of some theoretical AME models and discuss the possible impact of polarised AME on future primordial B-mode experiments.

Molecular hydrogen emission is commonly observed in planetary nebulae. Images taken in infrared H2 emission lines show that at least part of the molecular emission is produced inside the ionised region. In the best-studied case, the Helix nebula, the H2 emission is produced inside cometary knots (CKs), comet-shaped structures believed to be clumps of dense neutral gas embedded within the ionised gas. Most of the H2 emission of the CKs seems to be produced in a thin layer between the ionised diffuse gas and the neutral material of the knot, in a mini photodissociation region (PDR). However, PDR models published so far cannot fully explain all the characteristics of the H2 emission of the CKs. In this work, we use the photoionisation code \textsc{Aangaba} to study the H2 emission of the CKs, particularly that produced in the interface H^+/H^0 of the knot, where a significant fraction of the H2 1-0S(1) emission seems to be produced. Our results show that the production of molecular hydrogen in such a region may explain several characteristics of the observed emission, particularly the high excitation temperature of the H2 infrared lines. We find that the temperature derived from H2 observations even of a single knot, will depend very strongly on the observed transitions, with much higher temperatures derived from excited levels. We also proposed that the separation between the H_alpha and NII peak emission observed in the images of CKs may be an effect of the distance of the knot from the star, since for knots farther from the central star the NII line is produced closer to the border of the CK than H_alpha.