Multi-colour light variation of AGB stars observed with ISO ^*,**

¹ Institut für Astronomie, Türkenschanzstraße 17, 1180 Wien, Austria
² Instituto de Astrofísica de Canarias, and Departamento de Astrofísica, Facultad de Física, Universidad de La Laguna, 38271 La Laguna, Tenerife, Spain

Corresponding author: F. Kerschbaum, Franz.Kerschbaum@univie.ac.at

Received: 12 March 2001
Accepted: 8 June 2001

Abstract

New visual light curves and infrared multi-epoch photometry are presented for a sample of AGB-stars spectroscopically observed with ISO. While the ISO work is or will be presented elsewhere, the aim of this paper is to give an overview of the properties of the light change of the objects. This information is crucial for the interpretation of the valuable ISO material. Using the University of Vienna Twin Automatic Photoelectric Telescope (APT) we monitored the stars of our sample in the photometric bands V and I_C. We present the light curve of each object and derive the parameters of the current light change, such as period(s) and amplitude. Furthermore we give colours and colour variations for these objects. Our results allow us to derive some general results on semiregular and irregular variables. Only in less than 50% of the cases could we confirm the GCVS period. Moreover, we did not find any pronounced difference between SRb and Lb variables in the regularity of the light curve. The existence of rapid oscillations indicated by Hipparcos data could not be confirmed. In addition to the visual light changes we present new near infrared photometry data. Although typically only few data points are available, they can be viewed relative to the better-monitored visual light curves providing information on possible phase shifts and differences in amplitude in different parts of the spectrum. Furthermore, multi-epoch photometry allows us to derive mean colours for these objects.