POSTER PAPER 9.14
Microvariability Among Selected Long Period Variables
R.E.Stencel, T.A.Ostrowski-Fukuda, C.A.Jurgenson, & A.Phillips
Institute: University of Denver Observatories, www.du.edu
Contact Email: rstencel@phoenix.phys.du.edu
Abstract:
DeLaverny et al. (1998) reported short-term brightness variations in 15 percent of the 250 Mira or Long Period Variable stars surveyed using the HIPPARCOS satellite, with the broadband 340 to 890 nm Hp filter. The abrupt variations ranged 0.2 to 1.1 magnitudes, on time-scales between 2 to 100 hours, with a preponderance found nearer Mira minimum light phases. However, the sampling frequency was extremely sparse and requires confirmation because of potentially important dust-formation physics that can be revealed. We report here ground-based photometric observations of several of these objects that support and tend to confirm, the deLaverny et al. findings. In our observations, four out of five Miras sampled (XZ Her, HO Lyr, AU Cyg and AM Cyg) were found to have significant fluctuations over these same short time-scales (at 95% confidence level and higher), based on analysis of photometric variance, and F-tests. Interpretation of this micro-variation is offered in terms of dust formation episodes in the upper atmosphere of the star, and tests using interferometric visibility curves are proposed.
Index Keywords: Long Period Variable Stars; Mass Loss; CCD Photometry; Infrared Spectra; Interferometry
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Manuscript submitted: 2001-Dec-04
"The Future of Cool-Star Astrophysics", 2003, Eds. A. Brown,
G. M. Harper, & T. R. Ayres.
Proceedings of 12th Cambridge Workshop on Cool Stars, Stellar Systems,
& The Sun,
© 2003 University of Colorado.