Spectroscopic Determinations of Surface Gravities of Giant Stars, and Ultraviolet Observations of RR Lyrae and X ARIETIS.
Abstract
The surface gravities of four K giant stars, including the well known standard stars Arcturus (alpha Boo) and Aldebaran (alpha Tau) are determined from an analysis of the molecular dissociation equilibrium of OH. High resolution FTS spectra of the infrared ground state vibration-rotation lines of the OH Deltav = 1 and Delta v = 2 sequences were used in the analysis. The oxygen abundances were derived from the (OI) lines at 6300 and 6363A. Lifetimes for the OH Deltav = 2 sequence lines are derived based on the Werner et al. (1983) electric dipole moment function and rotationless Einstein A values. Additionally, the Deltav = 2 sequence OH lines are identified in the solar spectrum using the infrared atlas of Delbouille et al. (1981) and analyzed to establish the accuracy of the calculated lifetimes. Masses for the stars based on the derived gravities, measured parallaxes and angular diameters are also discussed. The results indicated by the OH/(OI) solutions for Arcturus are log g = 1.7 +/- 0.2 for an effective temperature of 4375 +/- 50K and a mass of 0.8 M_{rm Q}. The corresponding results for Aldebaran are log g = 1.0 +/- 0.5 using a temperature of 3860 +/- 100K and a mass of 0.7 M_ {rm Q}.. The surface gravities of 5 further G and K giants were determined from an analysis of the molecular equilibrium of MgH, the magnesium abundances being derived from visible and near infrared high excitation potential MgI lines. The MgH features used, near 5135A, are from the A-X system (0,0) band. The MgH/MgI gravities are compared to surface gravities derived based on an analysis of the ionization equilibrium of iron. It is found that the implied giant star masses are not significantly subsolar. Ultraviolet observations of RR Lyrae and X Arietis obtained with the Astronomical Netherlands Satellite (ANS) and the International Ultraviolet Explorer (IUE) satellite are also discussed. These observations are compared with light curves derived using model atmospheres and synthetic spectrum calculations in conjunction with angular diameters determined by Manduca et al. (1981) from photometry at longer wavelengths. A good agreement is found. These results represent an important independent confirmation of the distance and <{rm Mv}> obtained for these stars by Manduca et al. using a theoretically calibrated surface brightness relation.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1987
- Bibcode:
- 1987PhDT.........6B
- Keywords:
-
- Physics: Astronomy and Astrophysics;
- Abundance;
- Giant Stars;
- Ionization;
- K Stars;
- Stellar Gravitation;
- Stellar Mass;
- Astronomical Netherlands Satellite;
- Dipole Moments;
- Infrared Spectra;
- Iue;
- Light Curve;
- Spectrum Analysis;
- Astrophysics