Phase Dependent Spectroscopic Monitoring of Cepheid Variable Stars (Poster abstract)

Volume 37 number 2 (2009)

Bandon Decker

Matthew M. Beaky

Abstract

(Abstract only) Cepheid variables are pulsating yellow giant stars, with a surface temperature somewhat greater than that of the Sun. While Cepheids have been studied photometrically in great detail for many decades, the data on how the spectra of Cepheid variables change over time is relatively scarce. Of special interest is the O I triplet at 7774 Angstroms, because its variation over one cycle is related to the motion of unionized oxygen in the atmosphere of the star as it pulsates. Three classical Cepheid variables, FF Aquilae, T Vulpeculae, and SU Cygni were observed spectroscopically on fifteen nights at the Truman State University Observatory using a SBIG Self-Guiding Spectrograph and a 35-cm Meade LX200GPS telescope. Low resolution (5 Angstroms/pixel) were obtained from 3800 to 9500 Angstroms, as well as higher resolution spectra (1 Angstrom/pixel) from 7400 to 8150 Angstroms. For all three stars, the spectra clearly revealed the change in surface temperature as a function of phase. Further analysis of the spectroscopic data enabled us to create plots of the equivalent width of the O I triplet as a function of phase for FF Aql.