A search for diffuse absorption bands in carbon-rich stars -- I. Barium and related stars

The results of a search for interstellar and circumstellar absorption lines in high-resolution optical spectra of seven late-type stars are presented. All these stars are single-lined spectroscopic binaries with unseen companions, presumably white dwarfs. Some residual material indicative of recent mass transfer from an asymptotic giant branch (AGB) star might still be associated with the systems. Peculiar energy distribution and the sodium D 1 and D 2 lines give direct evidence about the material in the line of sight in some cases. Absorption features of simple carbon-bearing molecules (C 2 , CN) have been detected in most of the examined stars, confirming a carbon-rich nature of the corre…

An abundance analysis of the symbiotic star CH Cyg

The photospheric abundances for the cool component of the symbiotic star CH Cyg were calculated for the first time using high-resolution near-infrared spectra and the method of of standard LTE analysis and atmospheric models. The iron abundance for CH Cyg was found to be solar, [Fe/H] = 0.0+/-0.19. The atmospheric parameters and metallicity for CH Cyg are found to be approximately equal to those for nearby field M7 giants. The calculated [C/H] = -0.15, [N/H] = +0.16, [O/H] = -0.07, and the isotopic ratios of 12C/13C and 16O/17O are close to the mean values for single M giants that have experienced the first dredge-up. A reasonable explanation for the absence of barium star-like chemical pec…

Spectroscopic variability of IRAS22272+5435

A time series of high-resolution spectra was observed in the optical wavelength region for the bright proto-planetary nebula IRAS22272+5435 (HD235858), along with a simultaneous monitoring of its radial velocity and $BVR_C$ magnitudes. The object is known to vary in light, color, and velocity due to pulsation with a period of 132 days. The light and color variations are accompanied by significant changes in spectral features, most of which are identified as lines of carbon-bearing molecules. According to the observations, the $C_2$ Swan system and CN Red system lines are stronger near the light minimum. A photospheric spectrum of the central star was calculated using new self-consistent atm…

Lithium in metal-poor red giants

AbstractThe lithium abundance was calculated for five metal-poor red giant stars from Li i doublet at 6707 Å by fitting the observed high-resolution spectra with synthetic spectra. The lithium abundance was found to be low in all stars, logϵ(Li) ≤ 1.8, confirming lithium depletion on the red giant and asymptotic giant branch.

Signatures of pulsations and mass loss in the spectra of post-AGB stars

AbstractThe results of high-resolution spectroscopy and radial velocity monitoringa are presented for selected post-AGB candidate stars. Time series of high-resolution spectra for HD235858 shows spliting of low-excitation atomic lines and significant changes in the intensity of C2 and CN lines originated in the extended atmosphere significantly affected by pulsations and outflow. Mass ejection was confirmed for cool R CrB candidate stars DY Per, V1983 Cyg, and V2074 Cyg.

Spectroscopy of red giants in the open clusters NGC 1545 and Tr2

The results of local thermodynamic equilibrium (LTE) abundance analysis are presented for four red giants in the fields of open clusters NGC 1545 and Tr2. The membership of HD 27276, HD 27292 and HD 16068 was confirmed and the age of NGC 1545 was updated: log  age(yr) = 7.95. A mild deficiency of iron-group elements was found on average for NGC 1545 and Tr2, [Fe/H]=−0.13 and −0.07 with an uncertainty of about 0.08 dex. Oxygen and carbon are moderately depleted in all cluster giants, [O/Fe]=−0.23 ± 0.05 dex and [C/Fe]=−0.56 ± 0.07 dex on average. Nitrogen is enhanced, [N/Fe] values in range +0.4 to +1.2 dex, and lithium depleted. Sodium is slightly enhanced, [Na/Fe]=+0.26 ± 0.04 dex on avera…

DYNAMICAL PHENOMENA IN THE ATMOSPHERE OF THE PROTO-PLANETARY NEBULA IRAS 22272+5435

Radial velocity monitoring of the star HD 235858 confirmed regular variations with a peak-to-peak amplitude of about 10 km s–1 and a period of about 131.2 days. The light, color, and velocity variations are typical for RV Tauri stars. Splitting of low-excitation atomic lines was detected. The components are both blue- and redshifted relative to the systemic velocity. Significant variations are observed in the intensity of C2 and CN lines. Variable emission in the Hα profile, splitting of low-excitation atomic absorption lines, appearance of CN emission lines, blue wings of strong lines, and recent reddening give evidence of shocks and mass outflow obviously induced by atmospheric pulsations.

ERRATUM: “STUDIES OF VARIABILITY IN PROTO-PLANETARY NEBULAE. II. LIGHT AND VELOCITY CURVE ANALYSES OF IRAS 22272+5435 AND 22223+4327” (2013, ApJ, 766, 116)

HD 50975: a yellow supergiant in a spectroscopic binary system

Context. Recent detection of a yellow supergiant star as a possible progenitor of a supernova has posed serious questions about our understanding of the evolution of massive stars. Aims. The spectroscopic binary star HD 50975 with an unseen hot secondary was studied in detail with the main goal of estimating fundamental parameters of both components and the binary system. Methods. A comprehensive analysis and modeling of collected long-term radial velocity measurements, photometric data, and spectra was performed to calculate orbital elements, atmospheric parameters, abundances, and luminosities. The spectrum in an ultraviolet region was studied to clarify the nature of an unseen companion …

STUDIES OF VARIABILITY IN PROTO-PLANETARY NEBULAE. II. LIGHT AND VELOCITY CURVE ANALYSES OF IRAS 22272+5435 AND 22223+4327

We have carried out a detailed observational study of the light, color, and velocity variations of two bright, carbon-rich proto-planetary nebulae, IRAS 22223+4327 and 22272+5435. The light curves are based upon our observations from 1994 to 2011, together with published data by Arkhipova and collaborators. They each display four significant periods, with primary periods for IRAS 22223+4327 and 22272+5435 being 90 and 132 days, respectively. For each of them, the ratio of secondary to primary period is 0.95, a value much different from that found in Cepheids, but which may be characteristic of post-asymptotic giant branch (AGB) stars. Fewer significant periods are found in the smaller radia…

CIT 6: The Early Phase of PPN?

Photometric and spectroscopic studies for one of the early phase candidate for proto-planetary nebulae, the dust enshrouded extreme carbon star CIT 6, are presented.

A detailed spectroscopy of the carbon-rich star BD +57° 2161

An LTE abundance analysis based on high-resolution spectra is presented for the carbon-rich star BD +57° 2161, whose evolutionary status is unknown. With [C/Fe] = +0.4 dex and a mean s-process overabundance of [s/Fe] ≃ +1.5 dex the peculiar atmospheric composition of BD +57° 2161 is confirmed. The 12 C/ 13 C abundance ratio was found to be about 10. The mild iron deficiency, [Fe/H] = -0.2, supports the idea that BD +57° 2161 could be an old-disk-population object. Radial-velocity measurements confirm the binary nature of the star. Therefore the peculiar chemical composition could be due to the mass transfer from the secondary - AGB star in the past. Orbital parameters are estimated for anot…

THE BINARY NATURE OF CH-LIKE STARS

The evolved pulsating CEMP star HD112869

Radial velocity measurements, $BVR_C$ photometry, and high-resolution spectroscopy in the wavelength region from blue to near infrared are employed in order to clarify the evolutionary status of the carbon-enhanced metal-poor star HD112869 with unique ratio of carbon isotopes in the atmosphere. An LTE abundance analysis was carried out using the method of spectral synthesis and new self consistent 1D atmospheric models. The radial velocity monitoring confirmed semiregular variations with a peak-to-peak amplitude of about 10 km $s^{-1}$ and a dominating period of about 115 days. The light, color and radial velocity variations are typical of the evolved pulsating stars. The atmosphere of HD11…

The excitation of circumstellar C2in carbon-rich post-AGB object IRAS 22272+5435

Context. Observations of the circumstellar envelopes of post-asymptotic giant branch (post-AGB) stars provide information about their mass-loss history during the AGB phase and about the chemistry inside envelopes after that phase. Aims. We analyze visual observations of C2 molecule in absorption and millimeter and sub-millimeter observations of CO molecule in emission with the aim of determining the physical and chemical conditions in the circumstellar shell of the carbon-rich post-AGB star IRAS 22272+5435. Methods. We determined the column densities and excitation structure of C2 from equivalent width analysis of the molecular absorptions. The thermal and density structure of post-AGB she…