12C/13C in atmospheres of red giants and peculiar stars

We determine the carbon isotopic ratios in the atmospheres of some evolved stars in both globular clusters and the disk of our Galaxy. Analysis of 12CO and 13CO bands at 2.3 micron was carried out using fits to observed spectra of red giants and Sakurai's object (V4334 Sgr). The dependence of theoretical spectra on the various input parameters was studied in detail. The computation of model atmospheres and a detailed abundance analysis was performed in a self-consistent fashion. A special procedure for determining the best fits to observed spectra was used. We show, that globular cluster giants with [Fe/H] < -1.3 have a low 12C/13C = 4 +/- 1 abundance ration. In the spectra of Sakurai's object (V4334 Sgr) taken between 1997-98, the 2.3 micron spectral region is veiled by hot dust emission. By fitting UKIRT spectra we determined 12C/13C = 4 +/- 1 for the July, 1998 spectrum. CO bands in the spectra of ultracool dwarfs are modelled as well.Comment: Poster for IAU Symposium No. 228, "From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution", V. Hill, P. Francois & F. Primas, eds. (2005); 2 pages, ppt is available on ftp://ftp.mao.kiev.ua/%2f/pub/users/yp/12C13C_for_IAU228.pp

Ultracool dwarfs

We present results of modeling of spectra of M-, L-, T-dwarfs. Theoretical spectra are fitted to observed spectra to study the main parameters of the low-mass objects beyond the bottom of Main Sequence. Application of ``lithium'' and ``deuterium'' tests for assessment of ultra-cool dwarfs are discussed.Comment: Talk for MAO2004 Meeting (Kyiv, July 15-17, 2004), see more details on http://www.mao.kiev.ua/mao-2004/public.htm, 6 pages, 3fig

MgH lines in the spectrum of Arcturus

The synthetic spectra of MgH lines was computed for the grid of the model atmospheres and compared with observed spectrum of Arcturus. The parameters of the atmosphere of Arcturus log g=1.5 for Teff=4300 K were found by using the minimization procedure of differences between observed and computed spectra and compared our results of other studies.Comment: Work was presented at YSC'20 and will appear in AAS

Spectroscopic Variability of IRAS 22272+5435

A time series of high-resolution spectra was observed in the optical wavelength region for the bright proto-planetary nebula IRAS 22272+5435 (HD 235858), along with a simultaneous monitoring of its radial velocity and BV R C magnitudes. The object is known to vary in light, color, and velocity owing 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 atmospheric models. The observed intensity variations in the C 2 Swan system and CN Red system lines were found to be much larger than expected if due solely to the temperature variation in the atmosphere of the pulsating star. In addition, the molecular lines are blueshifted relative to the photospheric velocity. The site of formation of the strong molecular features appears to be a cool outflow triggered by the pulsation. The variability in atomic lines seems to be mostly due variations of the effective temperature during the pulsation cycle. The profiles of strong atomic lines are split, and some of them are variable in a timescale of a week or so, probably because of shock waves in the outer atmosphere

The metal rich abundance pattern - spectroscopic properties and abundances for 107 main-sequence stars

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, ©: 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We report results from the high resolution spectral analysis of the 107 metal rich (mostly [Fe/H]$\ge$7.67 dex) target stars from the Calan-Hertfordshire Extrasolar Planet Search program observed with HARPS. Using our procedure of finding the best fit to the absorption line profiles in the observed spectra, we measure the abundances of Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zn, and we then compare them with known results from different authors. Most of our abundances agree with these works at the level of $\pm$0.05 dex or better for the stars we have in common. However, we do find systematic differences that make direct inferences difficult. Our analysis suggests that the selection of line lists and atomic line data along with the adopted continuum level influence these differences the most. At the same time, we confirm the positive trends of abundances versus metallicity for Na, Mn, Ni, and to a lesser degree, Al. A slight negative trend is observed for Ca, whereas Si and Cr tend to follow iron. Our analysis allows us to determine the positively skewed normal distribution of projected rotational velocities with a maximum peaking at 3 km s$^{-1}$. Finally, we obtained a Gaussian distribution of microturbulent velocities that has a maximum at 1.2 km s$^{-1}$ and a full width at half maximum $\Delta v_{1/2}=$0.35 km s$^{-1}$, indicating that metal rich dwarfs and subgiants in our sample have a very restricted range in microturbulent velocity.Peer reviewedFinal Published versio

Photospheric acne at the bottom of the main-sequence: Doppler images of M4.5 - M9V stars

Starspots are an important manifestation of stellar activity and yet their distribution patterns on the lowest mass stars is not well known. Time series spectra of fully convective M dwarfs taken in the red-optical with UVES reveal numerous line profile distortions which are interpreted as starspots. New Doppler images of HU Del (GJ 791.2A; M4.5V), BL Ceti (GJ 65A; M5.5V) and UV Ceti (GJ 65B; M6V) at two epochs separated by three nights are presented. We find that contrast ratios corresponding to photosphere-spot temperature differences of only 100-400 K are sufficient to model the time series spectra of M4.5V - M9V stars. Starspots are reconstructed at a range of phases and latitudes with mean spot filling factors of only a few per cent. The distribution and low-contrast of the spots/spot-groups that we recover are likely to be responsible for the low amplitude photometric variability seen in late-M dwarfs. The stability of the spot patterns in the two sets of timeseries observations enables us to measure the latitude dependent differential rotation, which we find to be consistent with zer