EDP Sciences
Highlighted papers
LOFAR observations of PSR B0943+10 (Bilous et al.)
Thursday, 27 November 2014 08:00

Vol. 572
In section 7. Stellar structure and evolution

LOFAR observations of PSR B0943+10: profile evolution and discovery of a systematically changing profile delay in bright mode

by A. Bilous, J. Hessels, V. Kondratiev, et al. A&A 572, A52


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Mode switching, the almost discontinuous flipping of a pulsar between two distinct emission levels, is seen in a small population of pulsars. This paper studies one of the best examples, PSR B0943+10, using LOFAR 25-80 MHz and 110-190 MHz) observations.The authors use the profile to specify the structure of the emission region. (One feature of the pulses is a mapping between the frequency of the emission and its site of origin in the magnetosphere.) The observed B-mode profile delay is frequency-independent and is far too large for the spin-down rate; it may be a gradual movement of the emission cone, unlike the spin involving emission from different field lines. The observed profile delay and variation of the subpulse drift rate have similar dependence on time.

 
Figueira et al. / A. F. Lanza
Wednesday, 26 November 2014 08:00

Vol. 572
In section 10. Planets and planetary systems

On the correlation between stellar chromospheric flux and the surface gravity of close-in planets

by A.F. Lanza A&A 572, L6


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Revisiting the correlation between stellar activity and planetary surface gravity

by P. Figueira, M. Oshagh, V. Zh. Adibekyan, and N. C. Santos A&A 572, A51


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It has been noticed a few years ago that the chromospheric activity of stars with exoplanets appears to be correlated with the gravity of the planet itself. Stars with strong-gravity planets seem to be more active. Two papers published today revisit this problem. First, P. Figueira and collaborators revisit the problem with a dataset that is about three times larger than the original one. They confirm the correlation, but with a pinch of salt: the correlation appears significant when only relatively massive, short-period planets are considered but remains tentative when including the whole dataset. Second, A. Lanza proposes that this correlation (and also that it is strongest for close-in planets) may be explained by planet evaporation: Some of the matter lost by the planet will remain trapped for some time in the star's coronal field and can efficiently absorb photons emitted in the Ca II H & K lines, which are the indicators of chromospheric activity. In the continuum, however, the absorption is negligible. Planets with lower gravity tend to lose more mass and to more strongly suppress the indicators of chromospheric activity, thus explaining why their stars appear less active. This study shows that one should be careful when using chromospheric activity of stars as an age indicator. It motivates the detection and accurate characterization of many more exoplanetary systems in order to refine possible statistical tests.

 
Filamentary structure and Keplerian rotation in the high-mass star-forming [...] (Betran et al
Thursday, 06 November 2014 08:00

Vol. 571
In section 6. Interstellar and circumstellar matter

Filamentary structure and Keplerian rotation in the high-mass star-forming region G35.03+0.35 imaged with ALMA

by M.T. Beltran, A. Sanchez-Monge, R. Cesaroni, et al. A&A 571, A52


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Do massive stars form like low-mass stars? Massive stars play a fundamental role in the ecosystem of a galaxy, but because they are rare, little is known about the details of the their formation, at least in comparison to the formation of their lower mass siblings. Beltran et al. use ALMA observations of G35.03+0.35, the likely birth place of a B-type protostar, and find a filamentary structure fragmented into cores. One of them is core A, which harbors a hypercompact HII region. Position-velocity plots of the velocity gradient toward core A show clear signatures of Keplerian rotation and are consistent with the pattern of an edge-on Keplerian disk rotating about a star with a mass in the range 5–13 Msun. This result supports theoretical scenarios according to which high-mass stars, at least B-type stars, form through disk-mediated accretion.

 
The Solar Twin Planet Search. I. (Ramirez et al.)
Thursday, 27 November 2014 08:00

Vol. 572
In section 8. Stellar atmospheres

The Solar Twin Planet Search. I. Fundamental parameters of the stellar sample

by I. Ramirez, J. Melendez, J. Bean, et al. A&A 572, A48


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This paper presents a detailed spectroscopic follow-up for the largest sample of solar twins (88 in all) observed at high resolution and high signal-to-noise with the MIKE optical spectrograph at Magellan. These stars are part of an ESO Large Program planet-search experiment. The authors homogeneously measure the equivalent widths of iron lines and use strict differential excitation/ionization balance analysis to determine atmospheric parameters with unprecedented internal precision: σ(Teff) = 7 K, σ(log g) = 0.019, σ([Fe/H]) = 0.006 dex, and σ(vt) = 0.016 km s−1. Reliable relative ages and very precise masses were also estimated using theoretical isochrones. The root-mean-square scatter of the differences between stars is fully compatible with the observational errors, demonstrating that systematic uncertainties in the stellar parameters are negligible. The authors also find a tight activity–age relation for their sample, which validates the internal precision of the dating method. Furthermore, the authors find that the solar cycle is perfectly consistent with boththis trend and its star-to-star scatter. The fundamental parameters derived from this work will be useful for exploring the connections between planet formation and stellar chemical composition, as well as the link to galactic chemical evolution.

 
The mysterious optical afterglow spectrum of GRB 140506A at z = 0.889 (Fynbo et al.)
Wednesday, 19 November 2014 08:00

Vol. 571
In section 6. Interstellar and circumstellar matter

The mysterious optical afterglow spectrum of GRB 140506A at z = 0.889

by J.P.U. Fynbo, T. Krühler, K. Leighly, et al. A&A 572, A12


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Gamma-ray bursts (GRBs) are powerful tools used to probe the interstellar medium of distant star-forming galaxies. The present work tries to clarify the mystery of the peculiar afterglow spectrum of the z = 0.889 GRB 140506A. Using spectroscopy with ESO/X-shooter at several epochs after the burst and imaging and spectroscopy of the host galaxy obtained with the Magellan telescope, the authors try to understand the origin of the very unusual properties of the absorption towards this GRB. It appears that there are several components aligned along the line of sight: first, a very broad and strong dust extinction in the visible associated with Balmer lines and variable between the two epochs; second, an HII region, detected with H and He excited absorption lines; third, a cooler region detected by molecular absorption from CH+. All three components have different velocities.

 
Eyes in the sky: Interactions between asymptotic giant branch [...] (van Marle et al.)
Monday, 03 November 2014 13:51

Vol. 571
In section 6. Interstellar and circumstellar matter

Eyes in the sky: Interactions between asymptotic giant branch star winds and the interstellar magnetic field

by A. J. van Marle, N. L. J. Cox, and L. Decin A&A 571, A131


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This is the most comprehensive study to date of the effects of weak magnetic fields on the expansion of evolved star winds. While the basic result is to be expected — that the interstellar magnetic field produces distinctly elongated, aspherical structures — the details are important for issues such as turbulence, shock structures, and transport of stellar nuclear products (hence mixing in the interstellar medium). The models are compared to Herschel images of wind-blown bubbles, but this will also be important for future missions, such as JWST, as well as for polarization studies.

 

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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