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We report results from lithium abundance determinations using high resolution spectral analysis of the 107 metal-rich stars from the Calan-Hertfordshire Extrasolar Planet Search programme. We set out to understand the lithium distribution of the population of stars taken from this survey. The lithium abundance with account NLTE effects was determined from the fits to the Li I 6708 \AA~resonance doublet profiles in the observed spectra. We find that a) fast rotators tend to have higher lithium abundances, b) $\log$ N(Li) is higher in more massive/hot stars, c) $\log$ N(Li) is higher in less evolved stars, i.e. stars of lower \logg, d) stars with the metallicities $>$0.25~dex do not show the presence of lithium lines in their spectra, e) most of our planet hosts rotate slower, f) our estimate of a lower limit of lithium isotopic ratio is \Li $>$10 in the atmospheres of two SWP and two non-SWP stars. Measurable lithium abundances were found in the atmospheres of 45 stars located at distances of 20-170 pc from the Sun, for the other 62 stars the upper limits of log N(Li) were computed. We found well defined dependences of lithium abundances on \Teff, \vsini, and less pronounced for the \logg. In case of \vsini we see two sequences of stars: with measurable lithium and with the upper limit of log N(Li). About 10\% of our targets are known to host planets. Only two SWP have notable lithium abundances, so we found a lower proportion of stars with detectable Li among known planet hosts than among stars without planets. However, given the small sample size of our planet-host sample, our analysis does not show any statistically significant differences in the lithium abundance between SWP and stars without known planets., Comment: 19 pages, 6 tables, 13 figures, accepted by AA

We analyse the spectral energy distribution of the evolved carbon giant DY Per with a spectral synthesis technique. The red giant shows the photometric features of R CrB type stars. We derive the atmospheric parameters of DY Per using three variants of molecular line lists. We estimate Teff to be in the range 2900 < Teff < 3300 K. We adopted log g = 0. The star may be metal deficient and hydrogen deficient. The maximum possible carbon abundance in the star, [C]=0.94, provides the following atmospheric parameters: Tef=3100 K, [Fe/H] = 0, log(C/O)=0.6, [N/Fe] = 0, [H/He] = 0, with Jorgensen's line lists for the molecules C2 and CN., Comment: 4 pages, 2 tables, 3 figs, accepted by Odessa asronomical observatory Publ., 2009

The recurrent nova RS Oph undergoes nova eruptions every ~ 10-20years as a result of thermonuclear runaway on the surface of a white dwarf close to the Chandrasekhar limit. Both the progress of the eruption, and its aftermath, depend on the (poorly known) composition of the red giant in the RS Oph system. Our aim is to understand better the effect of the giant secondary on the recurrent nova eruption. Synthetic spectra were computed for a grid of M-giant model atmospheres having a range of effective temperatures 3200 < Teff < 4400 K, gravities 0 < log g < 1 and abundances -4 <[Fe/H] < 0.5, and fit to infrared spectra of RS Oph as it returned to quiescence after its 2006 eruption. We have modelled the infrared spectrum in the range 1.4-2.5 micron to determine metallicity and effective temperature of the red giant. We find Teff = 4100 +/- 100 K, log g = 0.0 +/- 0.5, [Fe/H] = 0.0 +/- 0.5, [C/H] = -0.8 +/- 0.2, [N/H] = +0.6 +/- 0.3 in the atmosphere of the secondary, and demonstrate that that inclusion of some dust `veiling' in the spectra cannot improve our fits., Comment: 6 pages, 5 figs, 1 table, to appear in A&A

We compute opacities for the electronic molecular band systems A 6Sigma+ -- X 6Sigma+ of CrH and CrD, and A 2Pi -- X 2Sigma+ of MgH and MgD. The opacities are computed by making use of existing spectroscopic constants for MgH and CrH. These constants are adjusted for the different reduced masses of MgD and CrD. Frank-Condon factors are used to provide intensities for the individual vibronic bands. These results are used in the computation of synthetic spectra between Tef = 1800 and 1200 K with an emphasis on the realisation of ``deuterium test'', first proposed by Bejar et al. (1999) to distinguish brown dwarfs from planetary mass objects. We discuss the possible use of CrD and MgD electronic bands for the "deuterium test". We find CrD to be the more promising of the two deuterides, potentially, the most useful bands of CrH/CrD are the Delta v = +1 and Delta v = -1 at 0.795 and 0.968 micron., Comment: 11 pages, 4 figs, 4 tables, accepted by MNRAS, revised version with the new D_o = 1.285 eV (Shayesteh et al., in prep.) for MgH

We present the results of modelling the 0.45--1 micron spectral energy distribution of V838 Mon for 2002 November. Synthetic spectra were calculated using the NextGen model atmospheres of Hauschildt et al. (1999), which incorporate line lists for H2O, TiO, CrH, FeH, CO, and MgH, as well as the VALD atomic line list. Fits to the observed spectra show that, in 2002 November, the effective temperature of V838 Mon was approximately 2000 +/-100 K. Our theoretical spectra show a comparatively weak dependence on log g. Preliminary analysis of the hot star observed together with V838 Mon shows it to be a normal B3V dwarf., Comment: 7 pages, 4 figs, accepted by A&A

We present the results of our analysis of a high resolution (R ~ 30000) infrared spectrum of V4334 Sgr (Sakurai's Object) around the first overtone CO bands, obtained in 1998 July. The 12CO and 13CO bands are well-resolved, and we compute synthetic hydrogen-deficient model atmosphere spectra to determine the 12C/13C ratio. We find 12C/13C ~ 4 +/-1, consistent with the interpretation of V4334 Sgr as an object that has undergone a very late thermal pulse., Comment: 5 pages, 7 figs, accepted by AAL

Theoretical spectral energy distributions were computed for a grid of hydrogen-deficient and carbon-rich model atmospheres of T(eff) in the range of 5000-6250 K and log g = 1.0 - 0.0 by the technique of opacity sampling, taking into account continuous, molecular band and atomic line absorption. These energy distributions were compared with the spectrum of V4334 Sgr (Sakurai's object) of April, 1997 in the wavelength interval 300-1000 nm. We show that (1) the shape of the theoretical spectra depends strongly on T(eff) but only very weakly on the hydrogen abundance; (2) the comparison of the observed and computed spectra permits to estimate T(eff) approximately 5500 K for V4334 Sgr in April, 1997, and its interstellar reddening (plus a possible circumstellar contribution) E(B-V) approximately 0.70., Comment: 7 pages, 8 figures, LaTeX, accepted by Astronomy and Astrophysics