We consider the metallicities and kinematics of nearby stars known to have planetary-mass companions in the general context of the overall properties of the local Galactic Disk. We have used Strömgren photometry to determine abundances for both the extrasolar-planet host stars and for a volume-limited sample of 486 F, G and K stars selected from the Hipparcos catalogue. The latter data show tha...

An updated classification scheme for transition O2–3.5 If∗/WN5–7 stars is presented, following recent revisions to the spectral classifications for O and WN stars. We propose that O2–3.5 If∗, O2–3.5 If∗/WN5–7 and WN5–7 stars may be discriminated using the morphology of Hβ to trace increasing wind density as follows: purely in absorption for O2–3.5 If∗ stars in addition to the usual diagnostics ...

Various light curve parameters are presented for the first 93 objects in a photometric survey of poorly studied variable stars. Stars from the General Catalogue of Variable Stars (GCVS) fainter than tenth magnitude, north of the equator which were classified as pulsating variables (but excluding the long period, semiregular, and irregular variables) were included. It is shown that two parameter...

We present K-band λ/∆λ ∼ 2600 spectroscopy of five stars (K ∼ 14-16 mag) within 0. " 5 of Sgr A*, the radio source associated with the compact massive object suspected to be a 2.6 x 10 6 M ⊙ black hole at the center of our Galaxy. High spatial resolution of ∼ 0. " 09, and good strehl ratios of ∼ 0.2 achieved with adaptive optics on the 10-meter Keck telescope make it possible to measure moderat...

Isotopic abundance ratios Mg:Mg:Mg are derived for 20 stars from highresolution spectra of the MgH A-X 0-0 band at 5140Å. With the exception of the weak G-band giant HR 1299, the stars are dwarfs that sample the metallicity range -1.8 < [Fe/H] <0.0. The abundance of Mg and Mg relative to the dominant isotope Mg decreases with decreasing [Fe/H] in fair accord with predictions from a recent model...

xvii Chapter 1 Motivation 1 Chapter 2 Stellar evolution, Compact Stars, Accretion discs and X-ray binaries 3 2.1 Stellar evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1 Star Formation . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1.1 Protostars . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1.2 Stellar Mass limits . . . . . . . . . . . . . . . . . . 5 ...

A short introduction is given to astrophysics of neutron stars and to physics of dense matter in neutron stars. Observed properties of astrophysical objects containing neutron stars are discussed. Current scenarios regarding formation and evolution of neutron stars in those objects are presented. Physical principles governing the internal structure of neutron stars are considered with special e...

The positions in the H-R diagram of strongly magnetic Ap and Bp stars are compared with those of normal main sequence stars of types B7 to F2, with a view to investigating possible differences in evolutionary status between magnetic and non-magnetic stars. The normal B7–F2 stars fill the whole width of the main sequence band with some concentration towards the ZAMS, whereas the magnetic stars a...

We have used precise radial velocity measurements of subdwarf-B stars from the Palomar-Green catalogue to look for binary extreme horizontal branch (EHB) stars. We have determined the effective temperature, surface gravity and surface helium abundance for 20 of the targets from new or existing blue spectra and have compiled published values for these quantities for all but one other. We identif...

Context. The interpretation of X-ray detections from Herbig Ae/Be stars is disputed as it is not clear if these intermediate-mass pre-main sequence stars are able to drive a dynamo and ensuing phenomena of magnetic activity. Alternative X-ray production mechanisms, related to stellar winds, star-disk magnetospheres, or unresolved late-type T Tauri star companions have been proposed. Aims. The c...