Irregular variables of type Lb. New JHKL'M-photometry for 160 stars

Astronomy and Astrophysics Supplement Series, Sep 1996

This paper presents new near infrared observations of 160 Irregular variables of type Lb in the filter bands. These measurements are supplemented by data for additional 56 stars taken from the literature. In total 220 datasets are available because of some multiple observations. From our sample, 216 stars have near infrared (NIR) photometry now. Our sample of visually bright Lb-variables displays very similar infrared properties when compared with SRa- and SRb-variables. Derived from NIR-two colour diagrams the oxygen-rich Lbs seem to have intermediate atmospheric conditions between Miras and normal giants. There may be a sligthly larger “contamination” with non AGB-giants than in the case of the semiregulars. Using only our IR-colours the S- and the Carbon-stars among the Lbs again are undistinguishable from SR-variables of the same chemistry.

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Irregular variables of type Lb. New JHKL'M-photometry for 160 stars

January Irregular variables of type Lb. New J H K L0M -photometry for 160 stars? F. Kerschbaum 2 C. Lazaro 0 1 P. Habison 2 0 Instituto de Astrof sica de Canarias , 38200-La Laguna, Tenerife , Spain 1 Dpto. de Astrof sica, Fac. de F sica, Universidad de La Laguna , 38200-La Laguna, Tenerife , Spain 2 Institut fu ̈r Astronomie der Universit ̈at Wien , Tu ̈rkenschanzstra e 17, A-1180 Wien , Austria | This paper presents new near infrared observations of 160 Irregular variables of type Lb in the J HKL0M lter bands. These measurements are supplemented by data for additional 56 stars taken from the literature. In total 220 datasets are available because of some multiple observations. From our sample, 216 stars have near infrared (NIR) photometry now. Our sample of visually bright Lb-variables displays very similar infrared properties when compared with SRa- and SRb-variables. Derived from NIR-two colour diagrams the oxygen-rich Lbs seem to have intermediate atmospheric conditions between Miras and normal giants. There may be a sligthly larger \contamination" with non AGB-giants than in the case of the semiregulars. Using only our IR-colours the S- and the Carbon-stars among the Lbs again are undistinguishable from SR-variables of the same chemistry. 1. Introduction For a long time Mira variables, OH/IR- and Carbonstars were the most frequently studied Asymptotic Giant Branch (AGB) objects. The Semiregular (types SRa and SRb) and the cool Irregular variables (Lb) { quite numerous groups of objects { have been almost neglected although their role within the evolution on the AGB and their overall properties are far from being understood. The can provide important constraints for theoretical models due to their di erent pulsational behaviour compared to the more frequently studied Mira variables. Fortunately, this situation has changed during the last years { at least in the case of the Semiregulars. In Kerschbaum & Hron (1992 , 1994, 1996, SR-Papers I, II, III respectively) and Kerschbaum (1995 , SR-Paper IIb) stellar properties of Semiregular variables (SRVs) derived from GCVS4 (Kholopov et al. 1985{88) , IRAS-PSC (1988 ) and IRAS-LRS (1986 ) as well as new near infrared photometry were used to divide this inhomogeneous group of objects into physically distinct classes and to probe their evolutionary status. A study by Jura & Kleinmann (1992) came to similar conclusions concerning the galactic distribution of these stars. Complementing our work on SRVs, cool Irregular variables should be analysed in an analogous way. From what is known about the luminosities of Irregular variables of type Lb and since this group contains also Carbon stars, a signi cant number of Lbs should be on the thermallypulsing AGB (see the review by Querci 1986) . However, Little et al. (1987) found no Technetium in the O-rich Lbs of their sample whose presence would be an evidence for a recent thermal pulse. Peters (1991) used data from the IRAS-mission for an analysis of the space distribution and the mass loss of the main three AGB-variables the Miras, the Semiregulars and the Irregulars. The main outcome concerning the latter is that Irregulars seem to have mass loss rates comparable to those of Semiregulars but smaller than those of Miras. He arrived at similar scale heights for all three groups except for the long period Miras which turned out to be more concentrated to the disk. In a study mainly devoted to Semiregulars, Jura & Kleinmann (1992) derived a galactic distribution of the Irregular variables comparable to that of \thin disk" Miras. Unfortunately, their sample was a mixture of Irregulars with a signi cant number of Semiregulars and Miras with unknown periods. Moreover, it was limited to objects with jbj 30 having GCVS and IRAS-data. All these restrictions did not allow a more detailed analysis. Nevertheless, these examples of recent publications in that eld demon- authors during three dedicated runs in 1994 and 1995 and strate the need for more work. an additional one (November `94) again in collaboration Since our approach needs data from the visual to the with C. Loup. These datasets are labeled `I' in Table 3. far infrared the rst step was to close the gap in the stars energy distributions between the visual GCVS4 data and the 12−100 m infrared range of the IRAS-PSC. We ob- 3. Oxygen-rich Lb-variables tained new JHKL0M -photometry and supplemented it by `photometrically compatible' data from the literature for a representative subsample of the Lb variables in the GCVS4. In order to derive bolometric magnitudes for volume limited samples of Lbs (compare SR-Paper I) { which we plan for a forthcoming paper { the objects presented in the paper will also act as prototypes providing us with the bolometric corrections needed for the stars lacking NIRdata. 2. Observations A sample of optically bright GCVS4 variables of type Lb was selected by means of the availability of good photometry in the IRAS- (...truncated)


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F. Kerschbaum, C. Lazaro, P. Habison. Irregular variables of type Lb. New JHKL'M-photometry for 160 stars, Astronomy and Astrophysics Supplement Series, 1996, pp. 397-405, Volume 118, Issue 3, DOI: 10.1051/aas:1996207