Yu. P. Lyubchik

Spectral energy distribution for GJ406

Original article can be found at: http://www.aanda.org/----Copyright The European Southern Observatory

INTERMEDIATE RESOLUTION NEAR-INFRARED SPECTROSCOPY OF 36 LATE M DWARFS

We present observations of 36 late M dwarfs obtained with the Keck II/NIRSPEC in the J band at a resolution of {approx}20,000. We have measured projected rotational velocities, absolute radial velocities, and pseudo-equivalent widths of atomic lines. Twelve of our targets did not have previous measurements in the literature. For the other 24 targets, we confirm previously reported measurements. We find that 13 stars from our sample have v sin i below our measurement threshold (12 km s{sup -1}) whereas four of our targets are fast rotators (v sin i > 30 km s{sup -1}). As fast rotation causes spectral features to be washed out, stars with low projected rotational velocities are sought for radial velocity surveys. At our intermediate spectral resolution, we have confirmed the identification of neutral atomic lines reported in McLean et al. We also calculated pseudo-equivalent widths of 12 atomic lines. Our results confirm that the pseudo-equivalent width of K I lines is strongly dependent on spectral types. We observe that the pseudo-equivalent width of Fe I and Mn I lines remains fairly constant with later spectral type. We suggest that these lines are particularly suitable for deriving metallicities for late M dwarfs.

Spectral analysis of high resolution near-infrared spectra of ultra cool dwarfs

Aims. We present an analysis of high resolution spectra in the J band of five ultra cool dwarfs from M6 to L0. Methods. We make use of a new ab initio water vapour line list and existing line lists of FeH and CrH for modelling the observations. Results. We find a good fit for the Mn I 12 899.76 A line. This feature is one of the few for which we have a reliable oscillator strength. Other atomic features are present but most of the observed features are FeH and H2O lines. While we are uncertain about the quality of many of the atomic line parameters, the FeH and CrH line lists predict a number of features which are not apparent in our observed spectra. We infer that the main limiting factor in our spectral analysis is the FeH and CrH molecular spectra.

Lithium and the 6Li-7Li isotope ratio in the atmospheres of some sharp-lined roAp stars

The λ 6708 Å and 6103 Å lithium lines in the high-resolution spectra of some sharp-lined roAp stars are analyzed using three spectral-synthesis codes STARSP, ZEEMAN2, and SYNTHM. The lines from the VALD database were supplemented with lines of rare-earth elements from the DREAM database and new lines calculated using the NIST energy levels. Our synthetic-spectrum calculations take into account magnetic splitting and other line-broadening effects. Lithium overabundances were found in the atmospheres of the stars based on our analysis of both lithium lines, along with high values of the 6Li-7Li isotope ratio (0.2–0.5). This can be explained if lithium is produced in spallation reactions and the surface 6Li and 7Li is preserved by strong magnetic fields in the upper layers of the stellar atmospheres, around the poles of the dipole field. The asymmetry of lithium lines to the red may be due to the action of shocks in the optically thin upper atmosphere, with the shocked material subsequently falling onto the star.

A detailed study of Lithium in 107 CHEPS dwarf stars

EU PF7 Marie Curie Initial Training Networks (ITN) RoPACS project 213646 Fondecyt grant 1161218 CATA-Basal (CONICYT) PB06 UK STFC ST/M001008/1 Leverhulme Trust RPG-2014-281 NAS Ukraine under the Main Astronomical Observatory GRAPE/GPU/GRID computing cluster project

Actinium Abundance in the Atmospheres of Three Red Supergiants in the Magellanic Clouds

The actinium abundance in the atmospheres of red supergiants PMMR23 and PMMR144 in the Small Magellanic Cloud and RM_1-667 in the Large Magellanic Cloud was estimated. The results of spectral observations with the ESO 3.6-m telescope with resolving power R = 30000 were used. Since actinium was not found in the atmospheres of PMMR23 and PMMR144, only the upper limits were set on its abundance: logN(Ac/H) <–15.1 and–15.0, respectively. The estimated abundance of actinium in the atmosphere of RM_1-667 varied with parameters of the atmospheric model from–14.1 to–13.3. The lines of ionized actinium λ 616.475 nm and λ 581.085 nm were used in this analysis.