Related papers: The carbon star DY Persei may be a cool R Coronae …

We have identified 139 cool carbon stars in the near-infrared spectro-photometric survey of the InfraRed Telescope in Space (IRTS) from the conspicuous presence of molecular absorption bands at 1.8, 3.1 and 3.8 microns. Among them 14 are…

We present newly processed archival Herschel images of molecular cloud MCLD 123.5+24.9 in the Polaris Flare. This cloud contains five starless cores. Using the spectral synthesis code Cloudy, we explore uncertainties in the derivation of…

For a complete 12 micron flux-limited sample of 207 IRAS sources, we have extracted light curves in seven infrared bands between 1.25 - 60 microns using the database of the DIRBE instrument on the COBE satellite. Using previous infrared…

The well-known light minima of stars with the R Coronae Borealis variability are caused by the formation of an additional circumstellar dust shell, the screening shell, inside the permanent shell. Under the assumption of uniform…

High-resolution optical spectra of R CrB obtained in 2003 March is discussed. The 2003 spectra are compared with the extensive collection of spectra from the 1995-1996 minimum. Spectroscopic features common to the two minima include sharp…

Cool white dwarfs with Teff < 6000 K are the remnants of the oldest stars that existed in our Galaxy. Their atmospheres, when properly characterized, can provide valuable information on white dwarf evolution and ultimately star formation…

Atomic carbon has been detected in the envelopes of three carbon-rich evolved stars: HD 44179 (=AFGL 915, the `Red Rectangle'); HD 56126; and, tentatively, the carbon star V Hya. This brings to seven the number of evolved star envelopes in…

We have measured the times of onset of recent fadings in four R CrB stars -- V854 Cen, RY Sgr, R CrB, and S Aps. These times continue to be locked to the stars' pulsation periods, though with some scatter. In RY Sgr, the onsets of fading…

We examine long-term low-dispersion IUE, SWP and LWP spectroscopy of the R Coronae Borealis (RCB) star V854 Cen, obtained across the deep 1991, 1992-1993 and 1994 declines. We also report the optical light curve for the star in the interval…

We describe a near-IR photometric search for cool red dwarf companions to hot EUV-detected white dwarfs (WDs). While some composite systems have been found optically among WDs detected in recent EUV All-Sky Surveys, we develop an IR…

AB Dor, Speedy Mic and Rst137B are in their early post-T Tauri evolutionary phase (<100Myr), at the age of fastest rotation in the life of late-type stars. They straddle the coronal saturation-supersaturation boundary first defined by young…

We present an analysis of 17 H-rich central stars of planetary nebulae (PNe) observed in our spectroscopic survey of nuclei of faint Galactic PNe carried out at the 10-m Hobby-Eberly Telescope. Our sample includes ten O(H) stars, four DAO…

Deuterium fractionation becomes highly efficient in cold, dense cores where CO is frozen out. Cyclopropenylidene (c-C3H2), an early-formed carbon ring, and its deuterated isotopologues trace gas-phase deuteration in these environments. We…

We have observed several cloud cores in the Orion B (L1630) molecular cloud in the 2-1 transitions of C18O, C17O and 13C18O. We use these data to show that a model where the cores consist of very optically thick C18O clumps cannot explain…

The results of spectral observations in the $\sim 84-92$ GHz frequency range of six objects in the southern sky containing dense cores and associated with regions of massive stars and star clusters formation are presented. The observations…

We have carried out a new photometric V,Rc study of 12 protoplanetary nebulae, objects in the short-lived transition between the AGB and PN phases of stellar evolution. These had been the subjects of an earlier study, using data from…

Massive stars have a strong impact on their local environments. However, how stellar feedback regulates star formation is still under debate. In this context, we studied the chemical properties of 80 dense cores in the Orion molecular cloud…

Cool stars on the main sequence generate X-rays from coronal activity, powered by a convective dynamo. With increasing temperature, the convective envelope becomes smaller and X-ray emission fainter. We present Chandra/HRC-I observations of…

Dwarf carbon stars make up the largest fraction of carbon stars in the Galaxy with around 1200 candidates known to date primarily from the Sloan Digital Sky Survey. They either possess primordial carbon-enhancements, or are polluted by mass…

The Galactic Center and inner disk of the Milky Way contain complex stellar populations obscured by heavy dust extinction. To study their chemical composition, high-resolution near-infrared (near-IR) spectroscopy is necessary. Expanding the…