Some Characteristics of
Variable Stars Appearing in Infrared Sky Surveys
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Edwin B. Weston
Optical Physics Laboratory,
Air Force Cambridge Research Laboratories, Bedford, MA 01731
Variable and suspected
variable stars are relatively numerous in infrared sky surveys carried out at
wavelengths of 2.2, 4, 11, and 20 microns. Most of these variables are of Mira,
semi-regular, and slowly varying irregular types with late (i.e., cool)
spectral classes and with giant or super-giant characteristics. Eclipsing
variables are represented, but most of them are of long period with Zeta
Aurigae of VV Cephei characteristics. Orbital data for these and a number of
other spectroscopic binaries indicate that they are more massive than the
average star. Other variables represent an assortment of the remaining types,
and they appear to represent the brightest members of those classes or to be
especially peculiar.
It is suggested that the
observed infrared variability of Mira stars, typically with amplitudes of 0.5
to 1.0 magnitude and approximately in phase with the visual light curve,
results primarily from changes in the temperature of circumstellar dust rings
or shells as a consequence of variations in the heating by activity centers in
the star's atmosphere not too dissimilar from the sun's plage areas
characterized by sunspots, flares, etc. The aspect angle at which we view these
presumably rotating stars may also be important, since the activity centers
will be nearer their equators than to the poles, and perhaps may be the cause
of differences in light curve and spectroscopic characteristics separating
certain of the semi-regular variables from the Mira stars.
The assistance of the AAVSO
provided in the form of preliminary visual light curves for a number of long
period variables is acknowledged with appreciation.
