08.11.2016

Nikolay Britavskiy (Odessa University, Ukraine)

Open issues in spectroscopy of RR Lyrae and red supergiant stars.

STRESZCZENIE In this talk, I will present some important problems in spectroscopy analysis of (i) RR Lyrae stars and (ii) red supergiants (RSGs). (i) I will present radial velocity analysis for 20 solar neighborhood RR Lyrae and 3 Population II Cepheids. We provide the new approach that used absorption line profile asymmetry to determine both the pulsation and the barycentric velocities even with a low number of high-resolution spectra and in cases where the phase of the observations is uncertain. This method is based on a Least Squares Deconvolution (LSD) of the line profiles in order to analyze line asymmetry that occurs in the spectra of pulsating stars. By applying this method to our sample stars we attain accurate measurements ($\pm$ 3 $km~s^{-1}$) of the pulsation component of the radial velocity. A detailed investigation of LSD profile asymmetry shows the variable nature of the project factor at different pulsation phases, which should be taken into account in the detailed spectroscopic analysis of pulsating stars. (ii) In the second part of my talk, I will present the identification and investigation of RSGs in dwarf irregular galaxies in the Local Group and beyond. Using the fact that RSGs are bright in mid-infrared colors due to dust, we applied a technique that allows us to select dusty massive stars based on their [3.6] and [4.5] Spitzer photometry. We applied our criteria to 7 dIrr galaxies: Pegasus, Phoenix, Sextans A, Sextans B, WLM, IC 10 and IC 1613 selecting 124 point sources. In total, we observed 124 targets, among which we identified 28 RSGs (21 are new discoveries) and 2 new emission line objects in these galaxies. These new discoveries are statistically significant and this sample increased the number of spectroscopically confirmed RSGs in dIrrs by 50%. Moreover, for the newly identified RSGs we measured the fundamental physical parameters by fitting their observational spectral energy distributions with MARCS stellar atmosphere models. This work serves as a basis for further investigation of the newly discovered dusty massive stars and their host galaxies.

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O PRELEGENCIE Nikolay Britavskiy obtained his M.Sc in Astrophysics in 2010 from the Odessa National University. During 2011-2012 years he worked in Bologna University under the Erasmus Mundus scholarship. In 2016 he obtained his PhD in Astrophysics from the University of Athens in collaboration with the National Observatory of Athens (NOA). Research Interests: Observational stellar astrophysics. Studies of the properties of dusty massive stars. Investigation of RR Lyrae and Cepheids variables. Studies of different spectroscopic techniques. Chemical analysis of semiregular variable stars.