Volume 458, Number 2, November I 2006
|Page(s)||533 - 539|
|Section||Stellar structure and evolution|
|Published online||12 September 2006|
Near-IR variability properties of a selected sample of AGB stars
Observatorio Astronómico Nacional, Apartado 112, 28803 Alcalá de Henares, Spain e-mail: firstname.lastname@example.org
2 FRACTAL SLNE, Avda San Sebastián 5 3-D, 38003 Santa Cruz de Tenerife, Spain
3 Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
4 Research and Scientific Support Department of ESA, European Space Astronomy Centre, Villafranca del Castillo, Apartado de Correos 50727, 28080 Madrid, Spain
5 Instituto de Astrofísica de Canarias, Via Lactea s/n, 38200 La Laguna, Tenerife, Spain
6 Consejo Superior de Investigaciones Científicas, Spain
Accepted: 8 June 2006
We present the results of a near-infrared monitoring programme of a selected sample of stars, initially suspected to be Mira variables and OH/IR stars, covering more than a decade of observations. The objects monitored cover the typical range of IRAS colours shown by O-rich stars on the asymptotic giant branch and show a surprisingly large diversity of variability properties. Sixteen objects are confirmed as large-amplitude variables. Periods between 360 and 1800d and typical amplitudes 1m 2m could be determined for nine of them. In three light curves, we find a systematic decrease in the mean brightness, and two light curves show pronounced asymmetry. One source, IRAS 07222–2005, shows infrared colours typical of Mira variables, but it pulsates with a much longer period (≈1200d) than a normal Mira. Two objects are either close to (IRAS 03293+6010) or probably in (IRAS 18299–1705) the post-AGB phase. In IRAS 16029–3041 we found a systematic increase in the colour of ≈1m, which we interpret as evidence of a recent episode of enhanced mass loss. IRAS 18576+0341, a heavily obscured luminous blue variable was also monitored. The star showed a continued decrease in brightness over a period of 7 years (1995–2002).
Key words: stars: AGB and post-AGB / stars: late-type / stars: variables: general / infrared: stars
© ESO, 2006
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