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V444 Cygni X-ray and polarimetric variability (Lomax et al.)
Friday, 12 December 2014 08:00

Vol. 573
In section 8. Stellar atmospheres

V444 Cygni X-ray and polarimetric variability: Radiative and Coriolis forces shape the wind collision region

by J.R. Lomax, Y. Naze, J.L. Hoffman, et al., A&A 573, A43


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Colliding winds have almost become a vogue in studies of massive binaries and none are better documented than those for the WN+O star binary V444 Cyg. The authors present a comprehensive, multiwavelength picture of the system's behavior including phase-resolved X-ray and optical spectrophotometry. A particularly novel feature of the study is their use of optical spectropolarimetry to constrain the scattering geometry. Then using hydrodynamic modeling they determine the respective roles of radiative braking on the structure of the standing shock, and the phase distortions of the variations due to the dynamics. They also constrain the soft X-ray emission to be beyond the substellar collision point.

 
The effect of external environment (E. I. Vorobyov et al.)
Wednesday, 10 December 2014 08:00

Vol. 573
In section 6. Interstellar and circumstellar matter

The effect of external environment on the evolution of protostellar disks

by E.I. Vorobyov, D.N.C. Lin, and M. Guedel A&A 573, A5


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The authors study the gravitational collapse of prestellar cores of subsolar mass embedded in a low-density external environment. They find that the infall of matter from the external environment can significantly alter the disk properties as compared to those seen in the isolated model. Depending on the magnitude and direction of rotation of the external environment, a variety of disks can form including both (i) compact disks (< 200 AU) shrinking in size because of the infall of external matter with low angular momentum and (ii) extended disks forming because of the infall of external matter with high angular momentum. The former are usually stable against gravitational fragmentation, while the latter are prone to fragmentation and formation of stellar systems with substellar or very-low-mass companions. In the case of counter-rotating external environment with high angular momentum, counter-rotating inner and outer disks separated by a deep gap at a few tens of AU can be formed. This model may lead to the emergence of a transient stellar system with substellar or very-low-mass components counterrotating with respect to the star.

 
Discovery of O VII line emitting gas in elliptical galaxies (Pinto et al.)
Wednesday, 03 December 2014 08:00

Vol. 572
In section 1. Letters

Discovery of O VII line emitting gas in elliptical galaxies

by C. Pinto, A. C. Fabian, N. Werner, P. Kosec, J. Ahoranta, J. de Plaa, J. S. Kaastra, J. S. Sanders, Y.-Y. Zhang, and A. Finoguenov A&A 572, L8


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Gas should be cooling on time scales of 1Gyr in the cores of galaxy clusters groups, and massive ellipticals, and a tracer of this cooling should be emission of the OVII line, which has never been detected yet in any object. The authors searched for this line in the archives of the RGS spectrometer of XMM-Newton and have discovered O VII resonance (21.6A) and forbidden (22.1A) lines for the first time in the spectra of 6 individual objects: 2 in Virgo and 4 others that are the dominant ellipticals of their groups. The O VII luminosities reveal a cooling rate of 0.2-2 Msun/yr corresponding to the predictions. Such OVII luminosities could not be detected in cool core clusters because of being farther away and because their spectra are dominated by the emission from hotter gas.

 
The elemental composition of the Sun (Scott et al.; Grevese et al.)
Thursday, 11 December 2014 01:04

Vol. 573
In section 9. The Sun

The elemental composition of the Sun I. The intermediate mass elements Na to Ca

by P. Scott, N. Grevesse, M. Asplund, et al. A&A 573, A25


The elemental composition of the Sun II. The iron group elements Sc to Ni

by P. Scott, M. Asplund, N. Grevesse, M. Bergemann, and A. J. Sauval A&A 573, A26


The elemental composition of the Sun. III. The heavy elements Cu to Th

by N. Grevesse, P. Scott, M. Asplund, and A. J. Sauval A&A 573, A27


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The chemical composition of the Sun is an essential piece of reference data for astronomy, cosmology, astroparticle physics, space physics, and geophysics: elemental abundances of essentially all astronomical objects refer to the solar composition, and basically every process involving the Sun depends on its composition. In this set of three papers, the authors present a comprehensive redetermination of the solar composition for the intermediate-mass elements (Na to Ca) in Paper I, all the iron group nuclei (Sc to Ni) in Paper II, and the heavy elements (from Cu to Th) in Paper III. In these papers the authors present the most accurate, homogeneous, and reliable results possible by employing a highly realistic 3D hydrodynamic model of the solar photosphere, which has successfully passed an arsenal of observational tests. They also carefully assess each transition probability, partition function, isotopic and hyperfine-splitting constant, and the observed spectrum of every line, making certain to only employ the best possible input data. This analysis provides a complete description and update of the results presented in Asplund, Grevesse, Sauval, & Scott (2009, ARA&A), including full details of all the lines and input data used.

 
The VISTA Carina Nebula Survey. I. (T. Preibisch et al.)
Thursday, 04 December 2014 08:00

Vol. 572
In section 14. Catalogs and data

The VISTA Carina Nebula Survey. I. Introduction and source catalog

by T. Preibisch, P. Zeidler, T. Ratzka, V. Roccatagliata, and M.G. Petr-Gotzens A&A 572, A116


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The authors used the 4m Visible and Infrared Survey Telescope for Astronomy (VISTA) of ESO to map an area of 6.7 square-degrees around the Carina Nebula in the near-infrared J-, H-, Ks-bands. The resulting catalog, which contains 3951580 sources, represents by far the most comprehensive deep near-infrared survey of the Carina Nebula complex and provides a new basis for investigating the young stellar population in this major star-forming complex.

 
Dusty tails of evaporating exoplanets. I. (van Lieshout et al.)
Monday, 01 December 2014 08:00

Vol. 572
In section 10. Planets and planetary systems

Dusty tails of evaporating exoplanets. I. Constraints on the dust composition

by R. van Lieshout, M. Min, and C. Dominik A&A 572, A76


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Two small evaporating exoplanets, KIC 12557548b and the recent KOI-2700b, were discovered by the Kepler mission from their variable transit lightcurves. Lieshout et al. model the structure of the comet-like tails and that of their grains to understand the amount and nature of the material lost. In order to constrain the composition of the micron-sized grains in the tails, they use the information available from these light curves, the size of grains required to scatter the starlight appropriately, and the length of the tails to model the thermal properties of rocky materials with standard compositions. Many compositions are ruled out (e.g., some grains would have to be too large in order to avoid being evaporated and explain the entire tail), leaving out as possible solutions only the most refractory materials (corundum, Al2O3, or iron-rich silicate minerals such as Fayalite, Fe2SiO4). These planets may thus have lost their more volatile elements in a first phase and now be slowly losing the most refractory material. The discovery of other examples of these rare evaporating planets combined with spectroscopic observations of their tails could help us to determine directly the interior structure of close-in planets.

 

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: N. Aghanim

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

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