Silicates in evolved stars: the lrs-maser chronology revisited
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Abstract
Since the publication of our correlation (1990 Ap.J. 350, L45) suggesting a temporal relationship among: (a) shapes of 10 micron silicates seen in IRAS Low Resolution Spectra (LRS); (b) IRAS broad band colors; (c) light curve asymmetries, and (d) the types of masers associated with various Mira variable stars, the question has arisen whether the implied chronology refelcts the interval between thermal pulses, or the more lengthy ascent of the AGB. There is evidence in favor of the former interpretation. A strong implication of this idea is that variability among pre-silicate spectra should be significant. Several examples of this have been found in the extended LRS database, and are presented. Finally, plans are presented to continue monitoring of selected variables in the 10 micron region, to verify the variability suggested in the limited phase coverage provided in the LRS database. Monitoring will include use of our facilities at the Mt.Evans-Womble Observatory — highest in the world at 4313 meters altitude.
Key words
circumstellar material IRAS infrared spectroscopyReferences
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