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The stripping of a galaxy group diving into the massive cluster A2142 (D. Eckert et al.)
Thursday, 30 October 2014 10:39

Vol. 570
In section 3. Cosmology

The stripping of a galaxy group diving into the massive cluster A2142

by D. Eckert, S. Molendi, M. Owers, et al. A&A 570, A119


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Large structures such as galaxy clusters form hierarchically in the universe by merging the subentities. Even though major mergers of clusters, like the bullet, are easy to see and study, and individual galaxies have also been frequently observed to fall inward and be stripped of gas in local clusters, such as Virgo or Coma, an infalling group is not very frequent. This work reports the discovery of a diffuse, irregular X-ray feature in the outskirts of the massive cluster Abell 2142, which is identified as an infalling galaxy group. The feature has a core-tail structure, where the core closer to the cluster center coincides with a group of galaxies. The tail pointing away from the cluster is 800kpc long, the longest X-ray tail ever reported. The gas of the tail is not as hot as the ambient X-ray gas, confirming it comes from a smaller structure. This is gas stripped from the infalling group. The 3D collisional velocity is approximately 1200 km/s. The survival of the tail in the hot X-ray medium of the cluster is 400 times longer than the conduction time scale. Conduction must be suppressed through a tangled magnetic field with a short coherence length and with plasma microinstabilities. With this long survival time, it is possible that the infalling material can eventually settle within the core of the main cluster.

 
Transit light curves of close-in planets (A. C. M. Correia)
Wednesday, 15 October 2014 08:00

Vol. 568
In section 1. Letters to the Editor

Transit light curve and inner structure of close-in planets

by A.C.M. Correia A&A 570, L5


Obtaining observational constraints on the internal structure of exoplanets is extremely challenging because it requires a measurement of the planet's shape or relies on rare dynamical configurations in multiple planet systems. This article shows that for exoplanets very close to their parent star, that they are tidally deformed by the star affects the lightcurves not just at ingress and egress but during the entire transit events. The signal may thus be within reach of future or even present space-based photometric. Such a determination would yield a measurement of the Love number k2 and could potentially help determine whether giant exoplanets have dense cores.

 
Reanalysis of the Benesov bolide and recovery of polymict breccia meteorites (Spurny et al.)
Tuesday, 14 October 2014 08:00

Vol. 570
In section 10. Planets and planetary systems

Reanalysis of the Benesov bolide and recovery of polymict breccia meteorites - old mystery solved after 20 years

by P. Spurny, J. Haloda, J. Borovicka, L. Shrbeny, P. Halodova, A&A 570, A39


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A&A press release. Astronomy & Astrophysics is publishing the spectacular discovery of meteorite fragments 20 years after the corresponding bolide was seen in the skies of the Czech Republic. This discovery was made possible by reanalyzing the trajectory that moved the impact line by 330 meters. Interestingly, the meteorites found on the ground are of different types, pointing to a parent asteroid of heterogeneous composition. Read the A&A press release.

 
Planck 2013 results
Friday, 17 October 2014 09:27

Vol. 571

A&A special feature: Planck 2013 results

Planck Collaboration, A&A, volume 571, November 2014


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A&A press release. Astronomy & Astrophysics is publishing a special feature of 31 articles describing the data gathered by Planck over 15 months of observations and released by ESA and the Planck Collaboration in March 2013. This series of papers presents the initial scientific results extracted from this first Planck dataset. Read the A&A press release.

 
A bag of tricks: Using proper motions of Galactic stars to identify [...] (Fabrizio et al.)
Wednesday, 15 October 2014 08:00

Vol. 570
In section 4. Extragalactic astronomy

A bag of tricks: Using proper motions of Galactic stars to identify the Hercules ultra-faint dwarf galaxy members

by M. Fabrizio, G. Raimondo, E. Brocato, et al. A&A 570, A61


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Ultra-faint dwarfs appear to be the least luminous, most dark-matter dominated, and most metal-poor galaxies known today. They consist of very sparse groups of stars that are superimposed upon a background of Milky Way stars. The main difficulties in accurately constraining the properties of these ultra-faint galaxies is to separate these overlapping stellar populations. The most accurate method is to measure the proper motions of all the stars in the field. Hercules is the prototype of this type of galaxy, and to remove the foreground (and background) contaminants, a proper-motion study was carried out using imaging from the Large Binocular Telescope (LBT). The datasets span a time baseline of about five years which allowed the authors to measure relative stellar proper motions of 528 sources to a precision of better than 5 mas yr−1 and distinguish a significant fraction (>90%) of Milky Way contaminants. The authors then compared the resulting cleaned color-magnitude diagram with stellar models, and confirmed that Hercules contains an old population (t =12±2 Gyr) with a wide spread in metallicity (−3.3<[Fe/H]<−1.8).

 
TANAMI monitoring of Centaurus A (Müller et al.)
Wednesday, 01 October 2014 08:00

Vol. 569
In section 10. Planets and planetary systems

TANAMI monitoring of Centaurus A: The complex dynamics in the inner parsec of an extragalactic jet

by C. Müller, M. Kadler, R. Ojha, et al. A&A 569, A115


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VLBI monitoring has revealed striking structures on subparsec scales in the radio jet of Centaurus A (Cen A). The proper motions over 3.5 years of individual jet components have been followed every six months at 8.4 GHz with the Australian Long Baseline Array (LBA) and associated telescopes in Antarctica, Chile, New Zealand and South Africa, complemented by quasi-simultaneous 22.3 GHz observations. They show apparent component speeds within 0.1c to 0.3c, with some varying higher speed differential motions superposed on a long-term stable feature. The interpretation is in terms of a spine-sheath structure with a faster inner jet and downstream acceleration where the jet becomes optically thin. The flow appears to be interrupted by an obstacle causing a local decrease in surface brightness and circumfluent jet behavior. A jet-star interaction could explain these features.

 

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

Mirror sites: CDS | EDP Sciences
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