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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


alt

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.

 
Detecting the spin-orbit misalignment of the super-Earth 55 Cancri e (Bourrier & Hébrard)
Wednesday, 24 September 2014 08:00

Vol. 569
In section 10. Planets and planetary systems

Detecting the spin-orbit misalignment of the super-Earth 55 Cancri e

by V. Bourrier and G. Hébrard A&A 569, A65


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The angle between the orbital plane of planets and the equatorial plane of their parent stars may be measured during transit events, thanks to the so-called Rossiter-McLaughlin effect. Obtaining sufficient signal-to-noise ratio generally requires the planet to be Jupiter-like and the star to rotate relatively rapidly. Bourrier and Hébrard use HARPS-N to detect the effect on 55 Cnc e, a small "super-Earth" that is only 8 times more massive than the Earth, taking advantage of the brightness of the star that is visible to the naked eye and of the proximity of the planet (an orbital period of only 0.74 day). This is the first time that this has been done for a planet with such low mass and in a planetary system. (The 55 Cnc system harbors at least 5 planets.) They find that the planet's orbit is highly misaligned compared to the star's spin, which is a surprise. It remains to be seen whether this is the rule or the exception.

 
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.

 
KIC10553698: An sdBV+WD binary (R. H. Østensen et al.)
Wednesday, 10 September 2014 12:49

Vol. 568
In section 7. Stellar structure and evolution

Asteroseismology revealing trapped modes in KIC 10553698A

by R. H. Ostensen, J. H. Telting, M. D. Reed, A. S. Baran, P. Nemeth, and F. Kiaeerad A&A 568, A15


Most hot subdwarf-B (sdB) stars belong to the population of extreme-horizontal-branch (EHB) stars. Several binary scenarios have been identified that can produce EHB stars, including either common-envelope ejection or stable Roche-lobe overflow. The sdBs pulsate with short (p modes) and long periods (g modes) because of the iron-group elements opacity bump (kappa mechanism). A key element in driving pulsations in sdBs is the competition between radiative levitation and gravitational settling, which causes a local overabundance of iron in the driving zone. KIC 10553698A is one of 16 sdBs observed with one-minute sampling rate for most of the duration of the Kepler mission. The authors identify the rich g-mode pulsation modes as components of rotationally split multiplets in a star rotating with a period of ~41 d. They are able to detect for the first time l = 1 modes that interpose in the asymptotic period sequences and that provide a clear indication of mode trapping in a stratified envelope, as predicted by theoretical models. A clear periodicity is also present in the Kepler photometry at 3.387 d. Spectroscopic observations reveal a radial-velocity amplitude of 64.8 km/s, indicating that the companion must be a white dwarf with a mass close to 0.6 M_o.

 

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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