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Chemodynamics of the Milky Way. I. (Anders et al.)
Wednesday, 16 April 2014 12:39

Vol. 564
In section 10. Galactic structure, stellar structure and populations

Chemodynamics of the Milky Way. I. The first year of APOGEE data

by F. Anders, C. Chiappini, B. X. Santiago, et al., A&A 564, A115


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In this paper, the first year of APOGEE (Apache Point Observatory Galactic Evolution Experiment) data, 57 000 red giant branch stars are used to investigate the chemo-dynamical properties of the disk of the Milky Way. This multi-object high-resolution near-infrared spectroscopic survey is able to peer through the dust that obscures stars in the Galactic disk and bulge at optical wavelengths. The sample extends up to 10kpc from the Sun, but the majority of red giants observed are at a distance of 1-6kpc from the Sun. This study increases the number studied in this way (by the RAVE and SEGUE surveys) by a factor 8. These results confirm a gap in the Fe-alpha diagram. That the number of stars with high-alpha/fe ratios decreases toward the outer parts of the Galactic disk suggests that the scale length of the thick disk is shorter than that of the thin disk. For stars high above the plane, with 1.5 < z < 3 kpc a positive metallicity gradient and a negative gradient in [ alpha/Fe] is reported.

 
Eclipsing Am binary systems in the SuperWASP survey (Smalley et al.)
Tuesday, 08 April 2014 08:50

Vol. 564
In section 14. Catalogs and data

Eclipsing Am binary systems in the SuperWASP survey

by B. Smalley, J. Southworth, O.I. Pintado, et al., A&A 564, A69


One subclass of chemically peculiar A and F stars are the Am stars, which have weaker CaII K lines than expected from their spectral type. It has been shown that the number of binaries found among Am stars is high, but the number of known eclipsing systems is surprisingly low (only 1.4%). This article presents a large-scale systematic search for eclipsing systems among Am stars observed with the SuperWASP camera. A total of 70 eclipsing systems were found (28 previously unknown) among the 1742 Am stars included in the survey. The fraction of eclipsing systems (4%) is consistent with the fraction of spectroscopic binaries.

 
The Gaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster (Jeffries et al.)
Friday, 14 March 2014 13:56

Vol. 563
In section 5. Galactic structure, stellar clusters and populations

The Gaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

by R.D. Jeffries, R.J. Jackson, M. Cottaar, et al., A&A 563, A94


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The Gamma Velorum cluster includes a massive young Wolf-Rayet binary system (γ^2 Vel), and it has been one of the first targets of the GAIA-ESO survey. The aim of this study has been to measure the kinematic properties of the low-mass stars as a means to probe the dynamical history of the cluster and to consider how these low-mass stars may populate the surrounding field as they become unbound. Intermediate-resolution VLT/FLAMES spectra were taken for 1242 unique targets around the Li I 6708 Angstrom line, and they were used to derive precise velocities, cluster membership probabilities, and the ages of each star. The authors found that the Gamma Velorum cluster consists of two kinematic components, one of which covers a narrow velocity range, and the other that is broader, 1-2 Myr younger, and slightly offset in velocity. The authors interpret these results as showing that one component is a bound remnant of the original dense cluster that formed the Wolf-Rayet binary (γ^2 Vel) system, and the other is a dispersed population from the wider stellar association. The apparent youth of γ^2 Vel (~3-4 Myr old) compared to the older (≥ 10 Myr) low-mass population surrounding it suggests that the massive binary system formed in a clustered environment after the formation of the bulk of the low-mass stars. It is possible that the formation of the massive binary system terminated star formation in the cluster by expelling all the gas.

 
Stochastic pulsations in the subdwarf-B star KIC 2991276 (Ostensen et al.)
Friday, 11 April 2014 11:10

Vol. 564
In section 1. Letters

Stochastic pulsations in the subdwarf-B star KIC 2991276

by R. H. Østensen, M. D. Reed, A. S. Baran, and J. H. Telting, A&A 564, L14


The subdwarf-B star KIC2991276 was monitored with the Kepler spacecraft for nearly three years. Two pulsation modes with periods of 122 and 132 s, as well as a few weaker modes with periods ranging from 118 to 216 s were detected. The modes in KIC 2991276 do not display long-term coherency, in contrast to other subdwarf-B pulsators. Instead, the pulsations in KIC 2991276 lose coherence on timescales longer than ~60 days. Stochastic oscillations are commonly observed in the Sun and other cool stars, but this is the first unambiguous detection in a hot subdwarf. The authors discuss possible causes of this phenomenon.

 
Warm formaldehyde in the Ophiuchus IRS 48 transitional disk (van der Marel et al.)
Tuesday, 18 March 2014 09:15

Vol. 563
In section 10. Planets and planetary systems

Warm formaldehyde in the Ophiuchus IRS 48 transitional disk

by N. van der Marel, E.F. van Dishoeck, S. Bruderer, T.A. van Kempen, A&A 563, A113


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So-called transitional disks with a hole in the dust distribution around the central star are a hot topic in the study of young pre-main-sequence stars. One of the fascinating results obtained with ALMA has been the discovery that the dust distribution of the disk surrounding the YSO Oph 48 is asymmetric, with an arc of emission to the south of the central star. It is hypothesised that this is caused by a sub-stellar companion or planet at a distance of 20 AU from the central star. The article by Van der Marel et al. highlighted in this issue shows that there also is an arc of molecular line emission (caused by formaldehyde in this case) slightly closer to the star than the continuum emission. The kinematics and spatial distribution are consistent with a ring of 60 AU radius, and the formaldehyde abundance of 10-8 relative to hydrogen suggests rapid ongoing chemical evolution

 
HR 5171 A: a massive interacting system in common envelope phase (O. Chesneau et al.)
Wednesday, 12 March 2014 12:47

Vol. 563
In section 7. Stellar structure and evolution

The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase

by O. Chesneau, A. Meilland, E. Chapellier, et al., A&A 563, A71


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HR5171 is a binary containing a yellow hypergiant. These are massive stars in a short-lived phase of their evolution. The authors present interferometric observations that are able to resolve the system. They show that the binary is a contact or over-contact system, making it one of the few resolved systems caught in a phase of mass transfer.

 

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

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

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