The stellar origin of the extremely hydrogen-deficient R Coronae Borealis (RCB) stars has remained a mystery for astronomers since their discovery more than two hundred years ago.  Two competing scenarios are commonly advocated. In the first one, a final helium shell flash occurs on a cooling white dwarf star or a very late thermal pulse is experienced by a post-AGB star. The second scenario involves the merger of two white dwarfs: a carbon–oxygen white dwarf accretes ahelium white dwarf. Evidence from the chemical compositions of RCB stars suggests that most are products of a merger

The effects that interactions produce on galaxy disks and how they modify the subsequent formation of bars need to be distinguished to fully understand the relationship between bars and environment. To this aim we derive the bar fraction in three different environments ranging from the field to Virgo and Coma Clusters, covering an unprecedentedly large range of galaxy luminosities (or, equivalently, stellar masses). We confirm that the fraction of barred galaxies strongly depends on galaxy luminosity. We also show that the difference between the bar fraction distributions as a function of

We use deep Hubble Space Telescope Advanced Camera for Surveys/High Resolution Channel observations of a field within M32 (F1) and an M31 background field (F2) to determine the star formation history (SFH) of M32 from its resolved stellar population. We find that 2-5 Gyr old stars contribute ~40% ± 17% of M32's mass, while ~55% ± 21% of M32's mass comes from stars older than 5 Gyr. The SFH additionally indicates the presence of young (<2 Gyr old), metal-poor ([M/H] ~ –0.7) stars, suggesting that blue straggler stars contribute ~2% of the mass at F1; the remaining ~3% of the mass is in young

Type-Ia supernovae are thought to occur when a white dwarf made of carbon and oxygen accretes sufficient mass to trigger a thermonuclear explosion. The accretion could be slow, from an unevolved (main-sequence) or evolved (subgiant or giant) star (the single-degenerate channel), or rapid, as the primary star breaks up a smaller orbiting white dwarf (the double-degenerate channel). A companion star will survive the explosion only in the single-degenerate channel. Both channels might contribute to the production of type-Ia supernovae, but the relative proportions of their contributions remain

Fullerenes and fullerene-related molecules have been proposed as explanations for unidentified astronomical features such as the intense UV absorption band at 217 nm and the enigmatic diffuse interstellar bands (DIBs), In order to shed light on the a long-standing DIB’s problem, we search high-resolution and high-quality VLT/UVES optical spectra of the hot R Coronae Borealis (RCB) star DY Cen for electronic transitions of the neutral C 60 fullerene molecule and DIBs. We report the non-detection of the strongest C 60 electronic transitions (e.g., those at ∼376, 398, and 402 nm). DIBs towards

We present observations and an interpretative model of the dust environment of the Main-Belt Comet P/2010 F5 (Gibbs). The narrow dust trails observed can be interpreted unequivocally as an impulsive event that took place around 2011 July 1 with an uncertainty of ±10 days, and a duration of less than a day, possibly of the order of a few hours. The best Monte Carlo dust model fits to the observed trail brightness imply ejection velocities in the range 8-10 cm s –1 for particle sizes between 30 cm and 130 μm. This weak dependence of velocity on size contrasts with that expected from ice