Allison Acosta Jason P. Aufdenberg Peter H. Hauschildt
Embry Riddle Aeronautical University Universitat Hamburg
Elemental abundances in the atmosphere of Sirius A reveal a history of nucleosynthesis. Sirius A, the brightest star in the night sky, has tightly constrained fundamental parameters due to its orbit w..
Elemental abundances in the atmosphere of Sirius A reveal a history of nucleosynthesis. Sirius A, the brightest star in the night sky, has tightly constrained fundamental parameters due to its orbit with Sirius B, a measured interferometric diameter, and a precise parallax. Its slow rotation and apparent lack of atmospheric convection suggest one-dimensional model atmospheres should be a good approximation. Recent abundance analyses of Sirius A from Landstreet (2011) and Cowley et al. (2016) have employed local thermodynamic equilibrium (LTE) models in comparison to high-resolution spectra from the Hubble Space Telescope Imaging Spectrograph (HST/STIS), the Goddard High Resolution Spectrograph (GHRS), and the Very Large Telescope Ultraviolet Visible Echelle Spectrograph (VLT/UVES). In order to perform an abundance analysis for Sirius A that does not assume LTE, we have employed the PHOENIX model atmosphere code to compute 1-D non-LTE models and spectra. We have thus far compared our non-LTE abundance results with literature values for 26 elements and find one element, Na, with a reduced abundance and six elements (Al, Sc, Mo, Cd, Dy, Lu) with elevated abundances. These results appear to differ from previous work for two reasons: (1) non-LTE models show enhanced ionization of trace species relative to LTE which depletes these species and elevates the abundance needed to match the observed spectrum, and (2) non-LTE departure coefficient values for specific lines differ significantly from unity.