Undergraduates have been important colleagues in this research, through NSF REU Supplements, Independent Study, as students at PARI, or in collaboration with other mentors/students. Students at ETSU made significant contributions to this work. Brian Heaton and Kevin Crowe have developed the IDL code necessary for wavelength calibration of the spectra. Eric Lingerfelt, Clayton Clark, and Rose Patrick have extended the program to include new Mira variables, and enhanced the program with BVRI photometry. Michael Bales has experimented with a novel spectrograph slit design for spectrophotometry. Erica Messer, from Valdosta State University spent the summer 1998 at ETSU as part of the SARA REU Program. She and I spent the summer acquiring spectra. Dr. Don Luttermoser and his SARA REU student, Rob Piontek, used the spectra, for the first time to determine log(g) and effective temperatures. Marie Rinkoski, another SARA REU student during the Summer 2000, took spectra, wrote a phase prediction program, and used the LTE code ATLAS to approximate the stellar atmosphere synthetic spectra.
Marie Rinkoski calculated, using ATLAS, log(g) and plotted Log(g)
vs Phase shown above. The plot shows minimum log(g) at phase 0.5
Marie Rinkoski also calculated the effective temperature versus phase.
The coolest temperature is at minimum light. Note that ATLAS is
LTE which provides only a rough approximation to Log(g) and Teff.
This research has been supported through an NSF CAREER grant, AST- 9500756, an American Astronomical Society Small Research Grant, and two NSF REU Supplements.
During the summer 2001, Andreas Schwietzer at the University of Georgis-Athens and his REU student Marcus Woo used our Mira spectra to model the stellar atmospheres. Woo and Schweitzer created a grid of model atmospheres to reproduce phase-resolved spectra of three Mira variables, R Leo, R CVn, and V CVn. The models produce good fits to the observed spectra. We have determined effective temperature variations with phase, and they are consistent with independent studies. However, changes in log(g) are too small to resolve. They used the AMES-dusty models that considerdust opacity in the atmosphere. The models confirmed V CVn and R CVn to be hotter stars than R Leo. The models also reflect the difference in visual magnitude variability in the three stars. The effective temperature and visual magnitude range for R CVn is largest, while the temperature and visual magnitude range for R Leo is the smallest. The models reproduce the VO and TiO bands well, with some deviations in regions of less flux. The determined effective temperature variations range from 2400-3100 K in R Leo, 3400-3600 K in V CVn, and 2800-3600 K in R CVn. Changes in log(g) cannot be resolved.