Variability and spectral classification of LMC giants: Results from DENIS and EROS ^*,**

¹ Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands
² Institute d'Astrophysique de Paris, CNRS, 98bis Bld. Arago, 75014 Paris, France
³ Observatoire de Marseille, LAM, 2 place Le Verrier, 13248 Marseille Cedex 4, France
⁴ Departement d'Astrophysique, Physique des Particules, Physique Nucleaire et d'Instrumentation associée (DAPNIA), Service de Physique des Particules (SPP), CEN Saclay, 91191 Gif-sur-Yvette Cedex, France
⁵ Max-Planck-Institut für Kernphysik, Postfach 10 39 80, 69029 Heidelberg, Germany

Corresponding author: M.-R. L. Cioni, mrcioni@strw.leidenuniv.nl

Received: 5 April 2001
Accepted: 6 August 2001

Abstract

We present the first cross-identifications of sources in the near-infrared DENIS survey and in the micro-lensing EROS survey in a field of about 0.5 square degrees around the optical center (OC) of the Large Magellanic Cloud. We analyze the photometric history of these stars in the EROS data base and obtain light-curves for about 800 variables. Most of the stars are long period variables (Miras and Semi-Regulars); a few Cepheids are also present. We also present new spectroscopic data on 126 asymptotic giant branch stars in the OC field, 30 previously known and 96 newly discovered by the DENIS survey. The visible spectra are used to assign a carbon-(C-) or oxygen-rich (O-rich) nature to the observed stars on the basis of the presence of molecular bands of TiO, VO, CN, C₂. For the remaining of the stars we used the () color to determine whether they are O-rich or C-rich. Plotting versus K_S we find three very distinct period-luminosity relations, mainly populated by Semi-Regular of type a (SRa), b (SRb) and Mira variables. Carbon-rich stars occupy mostly the upper part of these relations. We find that of the asymptotic giant branch population are long period variables (LPVs).