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Giant Stars (giant + star)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Eclipsing binaries in open clusters , III.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004
Persei, V621 Per in
ABSTRACT V621 Persei is a detached eclipsing binary in the open cluster , Persei, which is composed of an early B-type giant star and a main-sequence secondary component. From high-resolution spectroscopic observations and radial velocities from the literature, we determine the orbital period to be 25.5 d and the primary velocity semi-amplitude to be K= 64.5 ± 0.4 km s,1. No trace of the secondary star has been found in the spectrum. We solve the discovery light curves of this totally eclipsing binary and find that the surface gravity of the secondary star is log gB= 4.244 ± 0.054. We compare the absolute masses and radii of the two stars in the mass,radius diagram, for different possible values of the primary surface gravity, with the predictions of stellar models. We find that log gA, 3.55, in agreement with values found from fitting Balmer lines with synthetic profiles. The expected masses of the two stars are 12 and 6 M, and the expected radii are 10 and 3 R,. The primary component is near the blue loop stage in its evolution. [source]

Is the sky falling?

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
RAVE surveys, Searching for stellar streams in the local Milky Way disc in the CORAVEL
ABSTRACT We have searched for in-falling stellar streams on to the local Milky Way disc in the CORrelation RAdial VELocities (CORAVEL) and RAdial Velocity Experiment (RAVE) surveys. The CORAVEL survey consists of local dwarf stars (Nördstrom et al. Geneva,Copenhagen survey) and local Famaey et al. giant stars. We select RAVE stars with radial velocities that are sensitive to the Galactic vertical space velocity (Galactic latitude b < ,45°). Kuiper statistics have been employed to test the symmetry of the Galactic vertical velocity distribution functions in these samples for evidence of a net vertical flow that could be associated with a (tidal?) stream of stars with vertically coherent kinematics. In contrast to the ,Field of Streams' found in the outer halo, we find that the local volumes of the solar neighbourhood sampled by the CORAVEL dwarfs (complete within ,3 × 10,4 kpc3), CORAVEL giants (complete within ,5 × 10,2 kpc3) and RAVE (5,15 per cent complete within ,8 kpc3) are devoid of any vertically coherent streams containing hundreds of stars. This is sufficiently sensitive to allow our RAVE sample to rule out the passing of the tidal stream of the disrupting Sagittarius (Sgr) dwarf galaxy through the solar neighbourhood. This agrees with the most-recent determinations of its orbit and dissociates it from the Helmi et al. halo stream. Our constraints on the absence of the Sgr stream near the Sun could prove a useful tool for discriminating between Galactic potential models. The lack of a net vertical flow through the solar neighbourhood in the CORAVEL giants and RAVE samples argues against the Virgo overdensity crossing the disc near the Sun. There are no vertical streams in the CORAVEL giants and RAVE samples with stellar densities ,1.6 × 104 and 1.5 × 103 stars kpc,3, respectively, and therefore no evidence for locally enhanced dark matter. [source]

An elementary model for the dust cycle in galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2001
M.G. Edmunds
We give an elementary model for the evolution of dust in galaxies, based on abundance arguments. The model takes account of grain core production in both supernovae and giant stars, and includes mantle growth in the interstellar medium. Destruction of grain cores does not appear to be a dominant effect. We show that a self-consistent picture can be made in which the interstellar dust mass is an approximately constant fraction of the heavy element mass in the interstellar medium. This result is demonstrated to be essentially independent of outflow or inflow of interstellar material. [source]

Field optimization and CCD data simulation for the antarctic International Concordia Explorer Telescope (ICE-T)

ASTRONOMISCHE NACHRICHTEN, Issue 4 2009
D. Fügner
Abstract We performed extensive data simulations for the planned ultra-wide-field, high-precision photometric telescope ICE-T (International Concordia Explorer Telescope). ICE-T consists of two 60 cm-aperture Schmidt telescopes with a joint field of view simultaneously in two photometric bandpasses. Two CCD cameras, each with a single 10.3k × 10.3k thinned back-illuminated device, would image a sky field of 65 square degrees. Given a location of the telescope at Dome C on the East Antarctic Plateau, we searched for the star fields that best exploit the technical capabilities of the instrument and the site. We considered the effects of diurnal air mass and refraction variations, solar and lunar interference, interstellar absorption, overexposing of bright stars and ghosts, crowding by background stars, and the ratio of dwarf to giant stars in the field. Using NOMAD, SSA, Tycho-2 and 2MASS-based stellar positions and BVIJH magnitudes for these fields, we simulated the effects of the telescope's point-spread-function, the integration, and the co-addition times. Simulations of transit light curves are presented for the selected star fields and convolved with the expected instrumental characteristics. For the brightest stars, we showed that ICE-T should be capable of detecting a 2 REarth Super Earth around a G2 solar-type star, as well as an Earth around an M0-star , if these targets were as abundant as hot Jupiters. Simultaneously, the telescope would monitor the host star's surface activity in an astrophysically interpretable manner (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]