Viti, Serena; (1997) Infrared spectra of cool stars and sunspots. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis covers both the theoretical and the experimental aspects of cool and low mass stars' studies. In particular, it concentrates on M dwarfs which constitute about 88[percent] of our Solar neighbourhood. Although so numerous, the physics of M dwarfs is still poorly understood. Most of their energy (about 80%) is emitted between 1 and 5 microns, where strong absorption bands, caused mainly by the water molecule, are present. The interpretation of their colours and of their bolometric luminosities requires sophisticated modelling. The thesis is divided into two parts. The first part consists of the computation of molecular data of water. The applications of these data are various. For example some of these data are used for spectroscopic assignments of water lines in the sunspots. Some will be incorporated in the latest atmospheric models for cool stars. The codes employed calculate quantum mechanically the rotation-vibration energy levels, wavefunctions and associated dipole transition strengths of triatomic molecules. Two water linelists have been calculated and are widely described in this thesis; the first completed linelist, VTP1, has been computed with an accurate empirically determined potential energy surface. It contains all the energy levels and dipole transitions up to j = 38 belonging to the ground vibrational state and some of the ones belonging to the following vibrational bands: 100, 001, 010, 021, 101. The second linelist, ZVPT, has been computed with an ab initio potential energy surface. It includes all the rotational levels up to j = 33 and all the energy levels up to 20000 cm-1. A third, more comprehensive linelist, VT2, is partially complete. The second part of the thesis consists of the description of the observations, reductions and analysis of infrared data obtained with CGS4 (UKIRT) on several cool stars. Among these stars, I have also performed a detailed spectral analysis of the eclipsing binary system CM Draconis: I derived a direct measurement of its metallicity and effective temperature by direct comparison of the observed and synthetic spectra. I produced the synthetic spectra by using one of the latest model atmosphere codes.

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