Analyses of cool stars using molecular lines

• Main Author: Nordlander, Thomas
• Format: Others
• Language: English
• Published: Uppsala universitet, Teoretisk astrofysik 2012
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-174640

M-dwarfs are the coolest type of hydrogen-burning stars, and three times as numerous as all other stars in the Galaxy combined. Thanks to their low masses, luminosities and surface temperatures, they are potentially the best targets for finding exoplanets capable of supporting life. A low surface temperature unfortunately also allows the formation of various molecules, which complicates spectroscopic analyses. In this work, the molecular lines of titanium oxide (TiO) and various atomic lines are analyzed in a high-resolution (R ~ 68000) UVES spectrum of the M-dwarf GJ 876, as well as very high-resolution (R ~ 120000) spectra of five M-dwarfs. The TiO linelist is evaluated in a theoretical study of the molecular model. Results of the molecular line analysis are found to be misleading in certain regions. The strong TiO bands below wavelengths of 7300 Å indicate results incompatible with atomic lines at higher wavelengths. Instead, the TiO lines near 7700 Å are preferred. The theoretical study of the molecule improved both the precision and accuracy of transition wavelengths, but could not improve results of the molecular line analysis. The incompatible results are believed to stem from inaccuracies in the molecular line haze. Analyses in the wavelength range 7600-8800 Å are found to indicate consistent results, but residual accuracy problems cannot be excluded in the present analysis. Further study of M-dwarfs and improved modeling of TiO could resolve this issue, as well as lead to general improvements in the analyses of cool stars.