In recent years, large numbers of lithium-rich stars were discovered near several nearby star forming regions (SFRs). We present a detailed study of those stars discovered in and near the central region of the Taurus-Auriga T Tauri association, based on high-resolution echelle spectroscopy and proper motion data. We find that about 60 per cent of our sample can be regarded as pre-main sequence ...

We present high resolution spectra of the five known hydrogen-deficient carbon (HdC) stars in the vicinity of the 10830 Å line of neutral helium. In R Coronae Borealis (RCB) stars the He I line is known to be strong and broad, often with a P Cygni profile, and must be formed in the powerful winds of those stars. RCB stars have similar chemical abundances as HdC stars and also share greatly enha...

In this review we rst describe basic information for carbon stars starting with the most recent spectral classi cation system of P.C. Keenan and luminosities derived from data in the Hipparcos Catalogue. For the SRb and Lb variables MK = 6:8 1:2 (21 stars). Only two R stars (non-variables) have measured K magnitudes and showMK = 5:2. The four N stars show MV = +0:76 1:06. Using the Magellanic C...

The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of the chemical evolution of the Galaxy. In particular, these stars allow us to study the formation and evolution of the elements and the involved nucleosynthesis processes. This knowledge is invaluable for our understanding of the cosmic chemical evolution and the onset of starand galaxy...

We present a new spectroscopic classification for OB stars based on H−band (1.5 μm to 1.8 μm) observations of a sample of stars with optical spectral types. Our initial sample of nine stars demonstrates that the combination of He I 1.7002 μm and H Brackett series absorption can be used to determine spectral types for stars between ∼ O4 and B7 (to within ∼ ± 2 sub–types). We find that the Bracke...

Chemical composition is a good tracer of hydrodynamical processes that occur in stars as they often lead to mixing and particle transport. By comparing abundances predicted by models and those observed in stars we can infer some constraints on those mixing processes. As pulsations in stars are often very sensitive to chemical composition, we can use asteroseismology to probe the internal chemic...

We propose the new designation “WNH” for luminous Wolf-Rayet (WR) stars of the nitrogen sequence with hydrogen in their spectra. These have been commonly referred to as WNL stars (WN7h, for example), but this new shorthand avoids confusion because there are late-type WN stars without hydrogen and early-type WN stars with hydrogen. Clearly differentiating WNH stars from H-poor/Hfree WN stars is ...