M.-O. Mennessier

Long period variable stars: galactic populations and infrared luminosity calibrations

In this paper HIPPARCOS astrometric and kinematic data are used to calibrate both infrared lumi- nosities and kinematical parameters of Long Period Variable stars (LPVs). Individual absolute K and IRAS 12 and 25 luminosities of 800 LPVs are determined and made available in electronic form ? . The estimated mean kinematics is analyzed in terms of galactic populations. LPVs are found to belong to galactic populations ranging from the thin disk to the extended disk. An age range and a lower limit of the initial mass is given for stars of each population. A dierence of 1.3 mag in K for the upper limit of the Asymptotic Giant Branch is found between the disk and old disk galactic populations, conrming its dependence on the mass in the main sequence. LPVs with a thin envelope are distinguished using the estimated mean IRAS luminosities. The level of attraction (in the classication sense) of each group for the usual classifying parameters of LPVs (variability and spectral types) is examined.

Identification of RR Lyrae stars in the Tycho-2 catalogue

The Tycho-2 catalogue provides astrometric and photometric data for the 2.5 million brightest stars in the sky. Therefore it can provide much larger samples than the Hipparcos samples used to date in statistical studies. The object of this paper is the cross-identification of Tycho-2 sources and known variable stars of RR Lyrae type. The Tycho-2 data of cross-identified sources are added into the ASTRID specialized database. The present selection almost doubles the size of the sample of RR Lyrae stars with available proper motions.

Stellar and circumstellar evolution of long period variable stars

In a rst paper, HIPPARCOS astrometric and kinematic data were used to calibrate both infrared K and IRAS luminosities at the same time as kinematic parameters of Long Period Variable stars (LPVs). Individual estimated absolute magnitudes and a probabilistic assignation to galactic populations were deduced from these calibrations for each LPV of our sample. Here we propose a scenario of simultaneous stellar and circumstellar evolution according to the galactic populations. The transitory states of S and Tc stars allow us to conrm the location of the rst dredge-up at Mbol = 3:5. There is also evidence suggesting that a previous enrichment in s-elements from a more evolved companion may accelerate the evolution along the AGB. The possible evolution to OH LPVs is included in this scenario, and any of these stars may have a mass at the limit of the capability for a C enrichment up to C=O > 1. A list of bright massive LPVs with peculiar envelope and luminosity properties is proposed as Hot Bottom Burning candidates. The He-shell flash star, R Cen, is found to be exceptionally bright and could become, before leaving the AGB, a C-rich LPV brighter than the usual luminosity limit of carbon stars.

Group identification and individual assignation of stars from kinematical and luminosity parameters

The astrometric satellite HIPPARCOS has successfully finished its mission and the final data will be available in two years. As part of the effort to exploit these data we have developed a new Maximum Likelihood method to determine luminosity calibrations. This method includes several improvements: more realistic physical distributions, a detailed model of interstellar absorption and a built-in treatement of the effects of observational errors and sample selection. It is also able to identify, in a given sample, groups of stars with distinct physical characteristics. Once the groups are identified the stars in the sample can be assigned to them using a probability-based criterion.

Specific numerical and symbolic analysis of chronological series in view to classification of long period variable stars

For preparation of the astronomical space european mission HIPPARCOS, we got in charge of predicting the luminosity of long period variable stars for the whole duration of the flight (4 years).