Because of the tremendous densities that exist in the cores of neutron stars, a significant fraction of the matter in the cores of such stars is likely to exist in the form of hyperons. Depending on spin frequency, the hyperon content changes dramatically in rotating neutron stars, as discussed in this paper. PACS. 26.60 +c Nuclear matter aspects of neutron stars – 97.60.Gb Pulsars – 97.60.Jd N...

We present the results of binary population simulations of carbon-enhanced metalpoor (CEMP) stars. We show that nitrogen and fluorine are useful tracers of the origin of CEMP stars, and conclude that the observed paucity of very nitrogen-rich stars puts strong constraints on possible modifications of the initial mass function at low metallicity. The large number fraction of CEMP stars may inste...

Direct comparison of high-resolution X-ray spectra of the active dMe star AD Leo, observed three times with Chandra, shows variability of key density-sensitive lines, possibly due to flaring activity. In particular, a significant long-duration enhancement of the coronal density is indicated by the Ne IX and Si XIII He-like triplets, and possibly also by density-sensitive Fe XXI line ratios. Sub...

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 estimate the constraints of observational mass and redshift on the properties of equations of state (EOS) for quark matter based on the quasiparticle description in the compact stars. We discuss two scenarios: strange stars and hybrid stars. We construct the equations of state utilizing an extended MIT bag model taking medium effect into account for quark matter and relativistic mean field t...

The nature and evolutionary state of the diverse objects displaying the B[e] phenomenon are reasonably known, except for a rare subtype named FS CMa stars. These are surrounded by compact disks of warm dust whose origin is unclear. Although the luminosity of these objects corresponds to main-sequence stars, mass loss rates derived from emission lines are 2 orders of magnitude larger than predic...

We present our diagnosis of the role massive stars play in the formation of lowand intermediate-mass stars in OB associations. In the bright-rimmed and comet-shaped clouds in both the OriOB1 and LacOB1 associations, there is compelling evidence of lowand intermediate-mass star formation dominated by the triggering process by the massive stars in the regions. The expanding ionization fronts from...

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...

The recent catalog of spectral types of Galactic O-type stars by MáızApellániz et al. has been used to study the differences between the frequencies of various subtypes of O-type stars in the field, in OB associations and among runaway stars. At a high level of statistical significance the data show that Ostars in clusters and associations have earlier types (and hence presumably larger masses ...

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...