Variations in the L- and K-bands of 55 Cyg

HAUCKE M.; CAMPUZANO CASTRO F.

La Plata

Jornada; JAEDOC3; 2018

Facultad de Ciencias Astronómicas y Geofísicas de La Plata

The stellar wind is one of the most important phenomena to be taken into account in the theories of evolution of massive stars, since it can trigger large mass loss rates that could restrict the final evolutionary stages of the stars, i.e., could end up as a neutron star instead of a black hole. The study of stellar winds not only defines the evolution of the object per se, but also interferes with the chemical and dynamic evolution of galaxies, and may favor the formation of new objects.B supergiant stars (BSGs) are massive objects in either the preor post-red supergiant evolutionary stage and their out flowing material can be modeled very well by the standard theory of line-driven wind (Lucy & Solomon 1970 and Castor et al. 1975). But the behavior of these objects is not simple, since they show photometric and spectroscopic variations (Lefever et al. 2007, Morel et al. 2004, respectively), which could be considered as variations in the stellar photosphere and in the wind, but they are not predicted by the standard theory. This suggests that the ra-diation pressure is not sufficient to drive a stellar wind and that there should be another additional mechanism, which together with the radiation provide an explanation of the observed variations. In this way, one of the main proposed extra mechanisms that could connect the changes of the photosphere with those of the wind are the pulsations (Aerts et al. 2010), but observational data in various spectral ranges are necessary. In particular, infrared (IR) hydrogen lines, such as Brα and Brγ (L- and K-band, respectively), are very sensitive indicators of mass loss rates, and the variability of these lines could bring more informationabout the wind variation phenomena (Najarro et al. 2011). Here we present multi-epoch IR observations of 55 Cyg (B2.5I), taken with the GNIRS instrument in high-resolution mode. This object is of particular interest because its behaviuor is very variable. Kraus et al. (2015) reported multiperiodic variations in the radial velocity of optical photospheric lines, while the drastic changes in the shape and intensity of Hα profiles observed by Maharramov (2013), suggest high changes in the mass loss rate. We made an identification of the lines observed in both bands and analyze their equivalent widths (EW) via a line fitting procedure with a Python code. The line behaviour showed here will bring more information about of the variable nature of 55 Cyg and will allow us to discuss possible mechanism(s) responsible for the wind variations.