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Irregular variables of type Lb
Energy distributions and stellar parameters
Received 18 August 1999 / Accepted 28 September 1999
AGB variables of types Lb, SRa, SRb, and Mira are studied by fitting combinations of blackbodies to visual, near infrared and IRAS data. This paper supplements an earlier work dealing with a smaller sample of SRa and SRb variables. The fitted parameters , and are related to physically meaningful quantities. Also, quantities derived from the fits like the ratio of the luminosities of the two fitted blackbodies are confronted with independent mass-loss estimators.
For the O-rich Lb variables all of the `blue' objects can be reasonably well approximated by only one blackbody whereas the `red' ones need two. Among the `blue' objects a significant fraction seem to be not on the AGB at all but a kind of `RGB pollution'. The values, reflecting mainly offseted (-500 K) effective temperatures for objects with small to moderate mass-loss, are significantly higher in the `blue' cases.
Carbon-rich objects differ significantly from the O-rich ones in their fit parameters. Sometimes `unphysically' low are found - a result of circumstellar reddening in the high mass-loss cases. Furthermore lower values of , accompanied by normal s and large shell radii are common and can be related to the phenomenon of detached shells. S-stars populate a similar region to the optically thin carbon stars in their fit properties.
Key words: stars: AGB and post-AGB stars: variables: general stars: mass-loss infrared: stars
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Online publication: November 3, 1999