Is this project an undergraduate, graduate, or faculty project?

Undergraduate

individual

Authors' Class Standing

Allison Acosta, Senior

Lead Presenter's Name

Allison Acosta

Faculty Mentor Name

Jason Aufdenberg

Abstract

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.

Did this research project receive funding support from the Office of Undergraduate Research.

Yes, Spark Grant

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Chemical Abundances for Sirius using ERAU's Supercomputer Vega

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.