Long-Term Infrared Monitoring of Stellar Sources from Earth Orbit

Abstract

The 2.7µm radiation emitted by a selection of late-type variable stars during three years was monitored with U.S. Air Force satellite instrumentation. The data comprise the most detailed and extensive collection of infrared light curves reported for such stars and represent the first systematic infrared astronomy performed from Earth orbit. A well-defined linear increase in flux density is found to characterize the first three tenths of each cycle following infrared minimum of a long-period variable star. Examination of the data on long-period and semi-regular stars also shows marked differences between successive whole cycles, although there are certain phases at which the flux density repeats rather precisely. Large convective cells, as predicted for red supergiants, may couple with stellar pulsation in a manner that accounts for this phenomenon. The stars observed include known sources of circumstellar microwave line emission that may be pumped by the variable infrared continuum near the wavelength of observation. Strong coupling of large-scale convection and pulsation can give rise to the circumstellar clouds and, under certain conditions, may even provide the mechanism for ejection of material to form a planetary nebula.