Presented at the 87th
Spring Meeting of the AAVSO, June 20, 1998
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.