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T.A. Ostrowski, R.E. Stencel (Univ.Denver Observatories)
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 Astron. Astrophys. 330: 169). Nearly 15 percent of the 250 Miras surveyed in the broadband 380 to 800 nm filter showed variation of 0.2 to 1.1 magnitude on timescales of 2 to 100 hours, preferentially around minimum light phases.
We have begun an undergraduate thesis project to confirm these variations, using the 72cm/AP7 MBT at Mt.Evans, and 20cm/ST5 "Roboscope" at Chamberlin Observatory (www.du.edu/~rstencel). These new data will be used 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 (Muchmore, Nuth and Stencel 1987 ApJ 315:L141; Stencel et al. 1990 ApJ 350: L45). A progress report and call for observation coordination will be given.
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