Thomas F. Heinsheimer

Characteristics Of Ir Variable Stars As Observed From Orbit

We have studied a selection of infrared variable stars at wavelength 2.7 μm during 1971-1975 with data from U.S. Air Force satellites. Stars observed in this program are classified as long-period variable stars, semiregular variables, and irregular variables and are among the strongest stellar sources at this wavelength. In addition, a few new, as yet unclassified variable stars were identified during the course of the investigation. Time scales of reproducible variations range from a few weeks to a few years, and amplitudes of variation are as large as a factor of three for stars with periods of order one year. The minimum infrared flux density of a long-period star repeats accurately from one cycle to the next, whereas the maximum flux density was found to be unstable. This behavior may be related to the propagation of shocks in the stellar atmosphere near the time of maximum light or to coupling between large-scale convection and pulsation. It suggests that phenomena in these stars be timed with respect to minimum phase, rather than maximum phase as done previously. Maximum infrared flux density occurs after maximum visible light, whereas the visible and infrared minima are essentially simultaneous. The correlation of 2.7 μm and radio emission line data from one, well-studied long-period variable is consistent with the hypothesis that the H2O and OH circumstellar masers are saturated, if pumped by the stellar infrared flux near 2.7 μm, as suggested by Litvak. However, an alternate model, namely that the radio maser clouds are pumped by long-wave infrared radiation, cannot be excluded.

Long-term infrared monitoring of stellar sources from earth orbit☆

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.

Distribution of astronomical sources in the second Equatorial Infrared Catalogue

Measurements of infrared (2.7-μm) source positions and flux densities have been derived based on an additional 60.6 hours of satellite observations beyond those considered in the preparation of the Equatorial Infrared Catalogue No. 1 (EIC-1). These data have been processed together with the EIC-1 data to produce EIC-2. The new catalogue differs from EIC-1 as follows: there are 1278 sources (vs. 896 in EIC-1); there is a larger percentage of unidentified sources (17% vs. 10%); there are increased numbers of sources identified with Two-Micron Sky Survey sources (101 more than in EIC-1), AFGL sources (38 more), AGK3 stars (91 more) and SAO stars (187 more).

DEVELOPMENT OF THE EQUATORIAL INFRARED CATALOGUE FROM SATELLITE DATA

More than 40,000 infrared measurements of stellar sources have been obtained since November, 1976 during the ongoing process of compiling an Equatorial Infrared Catalogue. Because of the problem of eliminating spurious sources, which has affected earlier space surveys, we are making an extensive effort to verify the sources by means of (a) repetitive observations by satellite sensors, (b) crosscorrelation with a large data base developed from ground-based and space surveys at other wavelengths, and (c) investigation of a significant subset of the sources with a ground-based infrared telescope. As sources are verified, they are transferred from a working list to a screened preliminary version of the catalogue. The catalogue comprises the only survey of a significant area of the sky that has been accomplished (or is presently planned) with positional accuracies of a few arc seconds at a wavelength of ≥ 2 µm.

High-Precision Infrared Sky Survey At Wavelength 2.7 μm

Preliminary results of an infrared survey of the equatorial sky zone (declinations 10° S to 10° N) with U. S. Air Force satellite sensors show that positions of previously unknown infrared sources are measured with an rms accuracy of 4 arc seconds, which is six times better than the best previous infrared survey. The search area per source for further study is thus 36 times smaller, so that identification of the infrared sources with optical objects in catalogs and sky photographs is facilitated, as is reacquisition of the sources with ground-based infrared telescopes. The survey extends the content of near-infrared source catalogs to lower flux densities and adds information at a wavelength not observable from the ground. Objects found in the survey include cool giants and supergiants, long-period and semi-regular variable stars, and sources identified with faint red stars visible on the Palomar Observatory Sky Survey.