Photometry of Hipparcos Variable Stars

Volume 27 number 1 (1999)

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Threse A. Ostrowski

Robert E. Stencel

Dept. of Physics and

Abstract

Among the discoveries reported by the Hipparcos team was the detection of short-term photometric fluctuations in several long period, or Mira, variables (de Laverny et al. 1998). Nearly 15 percent of the 250 Miras surveyed in the broadband 380 to 800 nm filter showed variation of 0.2 to 1.1 magnitudes on timescales of 2 to 100 hours, preferentially around minimum light phases. We have begun an observational effort to confirm these variations. We seek to correlate the behavior with ancillary information, such as optical and infrared spectra plus maser data, to determine whether the fluctuations can be understood as thermal instabilities or so-called molecular catastrophe (cf. Muchmore et al 1987; Stencel et al. 1990). A progress report and call for observation coordination are given.