We study 111 late-type stars found with optical follow-upobservations ofROSATAll-SkySurvey sources south of the Taurus molecular clouds. Some 30 of them have been claimed to be weak-line T Tauri stars, low-mass pre-main sequence (PMS) stars, based mainly on the presence of strong lithium 6708Å absorption in intermediate-resolution (∼ 1Å) spectra. We obtained single-order echelle spectra at blue...

We present high resolution (R ∼ 34,000) optical (6330 8750 Å) spectra obtained with the HIRES spectrograph on the W. M. Keck I telescope of stars in Taurus-Auriga whose circumstellar environment suggests that they are less evolved than optically revealed T Tauri stars. Many of the stars are seen only via scattered light. The sample includes 15 Class I stars and all Class II stars that power Her...

The mass of the outer convective zone in FGK main sequence stars decreases dramatically with stellar mass. Therefore, any contamination of a star’s atmosphere by accreted planetary material should affect hotter stars much more than cool stars. If recent suggestions that high metal abundances in stars with planets are caused by planetesimal accretion are correct, then metallicity enhancements in...

HIPPARCOS trigonometrical parallaxes make it possible to compare the location of Tc-rich and Tc-poor S stars in the Hertzsprung-Russell (HR) diagram: Tc-rich S stars are found to be cooler and intrinsically brighter than Tc-poor S stars. The comparison with the Geneva evolutionary tracks reveals that the line marking the onset of thermal pulses on the asymptotic giant branch (AGB)matches well t...

A sample of 1497 carbon stars in the Large Magellanic Cloud (LMC) has been observed in the red part of the spectrum with the 2dF facility on the Anglo-Australian Telescope. Of these, 156 have been identified as J-type (i.e. 13C-rich) carbon stars using a technique which provides a clear distinction between J stars and the normal N-type carbon stars that comprise the bulk of the sample, and yiel...

The kinematic structure of a sample of planetary nebulae, consisting of 23 [WR] central stars, 21 weak emission line stars (wels) and 57 non-emission line central stars, is studied. The [WR] stars are shown to be surrounded by turbulent nebulae, a characteristic shared by some wels but almost completely absent from the non-emission line stars. The fraction of objects showing turbulence for non-...

It is suggested that the three-segmented morphology of the soft X-ray emission from cluster and field stars may be understood in terms of the recent classification of rotating stars into three kinds: those lying on the convective sequence, on the interface sequence, or in the gap between them. Subject headings: open clusters and associations: general — stars: activity — stars: chromospheres — s...

ASTRONOMY AND ASTROPHYSICS Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new Slowly Pulsating B Stars Abstract. We present a classiication of 267 new variable B-type stars discovered by Hipparcos. We have used two diierent classiication schemes and they both result in only a few new Cephei stars, a huge number of new Slowly Pulsating B stars,...

Received ; accepted – 2 – ABSTRACT We present 5 filter photometry of 21 carbon stars, 15 asteroids, 15 cataclysmic variables, 6 metal-poor stars, 5 Cepheids, 1775 field stars, blue horizontal branch (BHB) stars and RR Lyrae stars in the globular clusters M 15 and M 2, two primary standards, and 19 secondary standards. The photometry was carried out using a filter set identical to that which wil...