Astron. Astrophys. Suppl. Ser. 140, 55-67

Period-Luminosity-Colour distribution and classification of Galactic oxygen-rich LPVs

I. Luminosity calibrations

D. Barthès¹ - X. Luri¹ - R. Alvarez² - M.O. Mennessier³

1 - Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Avda. Diagonal 647, E-08028 Barcelona, Spain
2 - Institut d'Astrophysique, CP 226, Université Libre de Bruxelles, Bd. du Triomphe, B-1050 Bruxelles, Belgium
3 - GRAAL (UPRES-A 5024 CNRS), Université Montpellier II, F-34095 Montpellier Cedex 05, France

Received February 24; accepted September 6, 1999

Abstract:

The absolute K magnitudes and kinematic parameters of about 350 oxygen-rich Long-Period Variable stars are calibrated, by means of an up-to-date maximum-likelihood method, using HIPPARCOS parallaxes and proper motions together with radial velocities and, as additional data, periods and V-K colour indices. Four groups, differing by their kinematics and mean magnitudes, are found. For each of them, we also obtain the distributions of magnitude, period and de-reddened colour of the base population, as well as de-biased period-luminosity-colour relations and their two-dimensional projections. The SRa semiregulars do not seem to constitute a separate class of LPVs. The SRb appear to belong to two populations of different ages. In a PL diagram, they constitute two evolutionary sequences towards the Mira stage. The Miras of the disk appear to pulsate on a lower-order mode. The slopes of their de-biased PL and PC relations are found to be very different from the ones of the Oxygen Miras of the LMC. This suggests that a significant number of so-called Miras of the LMC are misclassified. This also suggests that the Miras of the LMC do not constitute a homogeneous group, but include a significant proportion of metal-deficient stars, suggesting a relatively smooth star formation history. As a consequence, one may not trivially transpose the LMC period-luminosity relation from one galaxy to the other.

Key words: stars: variables: long period variables -- AGB -- fundamental parameters -- kinematics -- evolution