Vsini-s for late-type stars from spectral synthesis in K-band region

We analyse medium-resolution spectra (R\sim 18000) of 19 late type dwarfs in order to determine vsini-s using synthetic rather than observational template spectra. For this purpose observational data around 2.2 $\mu$m of stars with spectral classes from G8V to M9.5V were modelled. We find that the Na I (2.2062 and 2.2090 $\mu$m) and $^{12}$CO 2-0 band features are modelled well enough to use for vsini determination without the need for a suitable observational template spectra. Within the limit of the resolution of our spectra, we use synthetic spectra templates to derive vsini values consistent with those derived in the optical regime using observed templates. We quantify the errors in our vsini determination due to incorrect choice of model parameters \Teff, log $g$, $v_{\rm micro}$, [Fe/H] or FWHM and show that they are typically less than 10 per cent. We note that the spectral resolution of our data(\sim 16 km/s) limited this study to relatively fast rotators and that resolutions of 60000 will required to access most late-type dwarfs.Comment: 8 pages, 4 figures, 3 tables, accepted to the MNRA

Masses, Oxygen and Carbon abundances in CHEPS dwarf stars

Reproduced with permission from Astronomy & Astrophysics. © 2019 ESOContext. We report the results from the determination of stellar masses, carbon, and oxygen abundances in the atmospheres of 107 stars from the Calan-Hertfordshire Extrasolar Planet Search (CHEPS) programme. Our stars are drawn from a population with a significantly super-solar metallicity. At least 10 of these stars are known to host orbiting planets. Aims. In this work, we set out to understand the behaviour of carbon and oxygen abundance in stars with different spectral classes, metallicities, and V sin i within the metal-rich stellar population. Methods. Masses of these stars were determined using data from Gaia DR2. Oxygen and carbon abundances were determined by fitting the absorption lines. We determined oxygen abundances with fits to the 6300.304 Å O I line, and we used 3 lines of the C I atom and 12 lines of the C 2 molecule for the determination of carbon abundances. Results. We determine masses and abundances of 107 CHEPS stars. There is no evidence that the [C/O] ratio depends on V sin i or the mass of the star within our constrained range of masses, i.e. 0.82 5 km s -1) are massive stars.Peer reviewedFinal Published versio

Spectral energy distribution for GJ406

We present results of modelling the bulk of the spectral energy distribution (0.45–5 μm) for GJ406 (M6V). Synthetic spectra were calculated using the NextGen model atmospheres of Hauschildt et al. [6] and the incorporate line lists for H2O, TiO, CrH, FeH, CO, MgH molecules as well as the VALD line list of atomic lines. The computed water partition function is in a good agreement with the one obtained by Vidler & Tennyson [14]. A comparison of synthetic and observed spectra gives Teff = 2900 ± 100 K for this late M-dwarf.The William Herschel Telescope and United Kingdom Infrared Telescope are operated for the Particle Physics and Astronomy Research Council (PPARC). ISO is an ESA project with the participation of ISAS and NASA funded from member states. HST is a NASA project funded in part by ESA. This work was partially supported by a PPARC visitors grants from PPARC and the Royal Society. YP’s studies are partially supported by a Small Research Grant from American Astronomical Society. This research has made with the use of the SIMBAD database, operated at CDS, Strasbourg, France

A detailed study of Lithium in 107 CHEPS dwarf stars

Reproduced with permission from Astronomy & Astrophysics, © ESO 2018.Context. 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. Aims. We aim to set out to understand the lithium distribution of the population of stars taken from this survey. Methods. The lithium abundance taking account of non-local thermodynamical equilibrium effects was determined from the fits to the Li I 6708 Å resonance doublet profiles in the observed spectra. Results. We find that a) fast rotators tend to have higher lithium abundances; b) log N(Li) is higher in more massive and hot stars; c) log N(Li) is higher in stars of lower log g; d) stars with the metallicities >0.25 dex do not show the lithium lines in their spectra; e) most of our planet hosts rotate slower; and f) a lower limit of lithium isotopic ratio is 7Li/ 6Li > 10 in the atmospheres of two stars with planets (SWP) and two non-SWP stars. Conclusions. 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 T eff, V sin i, and less pronounced for the log g. In case of V sin i 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.Peer reviewe

IRON ABUNDANCES IN THE ATMOSPHERES OF HD10700 and HD146233

There are many different means to determine physical parameters of stars and their abundances by spectral analysis. In our work we draw our attention to the rotational and microturbulenc velocities as well as metallicities for the stars of known effective temperature and surface gravity. We carried fits of LTE synthetic spectra to the observed spectra of HD10700 and HD146233. These stars are knows aa solar-twins except slightly higher rotational velocities in both cases and higher magnetical activity i of HD10700. We adopted ABEL software (Pavlenko Ya.V.) to fit to HD10700, HD146233 spectra obtained on Camino Observatory, Chilie. Selected stars looks like. We compare our results with previous work of Valenti and Fischer (2005)