We carried out observations of bright optical carbon stars by the ISO SWS, and detected the absorption features of CO, CS, CH, SiS and HCN in N-type and SC-type stars. We found several characteristics of molecular absorption features corresponding to the spectral types. The CH fundamental bands in 3-4 μm in N-type stars are stronger than those in SC-type stars. On the other hand, the first over...

We present the parallaxes, measured by Hipparcos, for a sample of X-ray selected stars. The stars belong to the stellar sample of the Einstein Extended Medium Sensitivity Survey. They are all at galactic latitude |b| > 20 deg, and are generally far away from known star forming regions. Several of these stars show lithium abundance and activity level typical of very young stars with ages compara...

To properly understand the physics of upper main sequence stars it is particularly important to identify the origin of their magnetic fields. Recently, we confirmed that magnetic fields appear in Ap stars of mass below 3 M ⊙ only if they have already completed at least approximately 30% of their main-sequence lifetime [1, 2]. The absence of stars with strong magnetic fields close to the ZAMS mi...

New NTT/EMMI spectrophotometry of single WN2–5 stars in the Small and Large Magellanic Clouds are presented, from which He  λ4686 line luminosities have been derived, and compared with observations of other Magellanic Cloud WolfRayet stars from the literature. SMC WN3–4 stars possess line luminosities which are a factor of 4 times lower than LMC counterparts, incorporating several binary SMC ...

It is generally agreed that the tremendous densities reached in the centers of neutron stars provide a high pressure environment in which numerous particles processes are likely to compete with each other. These processes range from the generation of hyperons to quark deconfinement to the formation of kaon condensates and H-matter [1]. Another striking possibility concerns the formation of abso...

Red Dwarfs (main-sequence / dwarf M or dM) stars are the most common stars in the Galaxy. These cool, faint, low mass stars comprise over 75% of all stars. Because of their low luminosities (∼0.0008–0.06 of the Sun’s luminosity), the circumstellar habitable zones (HZs) of dM stars are located within ∼0.05–0.4 AU of the host star. Nevertheless, the prospect of life on a planet located within the...

We have identified five new R Coronae Borealis (RCB) stars in the Galactic bulge using the MACHO Project photometry database, raising the total number of known Galactic RCB stars to about 40. We have obtained spectra to confirm the identifications. The fact that four out of the five newly identified RCB stars are “cool” (Teff < 6000 K) rather than “warm” (Teff > 6000 K) suggests that the prepon...

We present new nearby stars extracted from a proper motion catalogue and having a DENIS counterpart. Their distances and spectral type are estimated using the DENIS colours. 107 stars are within 50 pc. 31 stars among them have previously measured distances. In addition, 40 stars may enter within the 50 pc limit depending on which population they belong to. 6 stars among them have already measur...

We have discovered lines of highly ionized fluorine (F  and F ) in the far-UV spectra of extremely hot (Teff=85 000–150 000 K) post-AGB stars. Our sample comprises H-rich central stars of planetary nebulae as well as H-deficient PG1159 stars. We performed non-LTE calculations and find strong F overabundances (up to 10−4 by mass, i.e., 250 times solar) in a number of PG1159 stars, while F is ...

We present the results of an extensive search for periodic and irregular variable pre-main sequence (PMS) stars in the young (2–4 Myr) open cluster NGC 2264, based on photometric monitoring using the Wide Field Imager (WFI) on the 2.2 m telescope on La Silla (Chile). In total, about 10600 stars with IC magnitudes between 9.8 mag and 21 mag have been monitored in our 34 ×33 field. Time series da...