The contribution of red dwarfs and white dwarfs to the halo dark matter

¹ Departament de Física Aplicada, Escola Politécnica Superior de Castelldefels, Universitat Politècnica de Catalunya, Avda. del Canal Olímpic 15, 08860 Castelldefels, Spain e-mail: gracia@fa.upc.es
² Institute for Space Studies of Catalonia, c/Gran Capità 2–4, Edif. Nexus 104, 08034 Barcelona, Spain
³ Institut de Ciències de l'Espai, CSIC, Campus UAB, Facultat de Ciències, Torre C-5, 08193 Bellaterra, Spain

Received: 18 March 2008
Accepted: 9 April 2008

Abstract

Context. The nature of the several microlensing events observed by the MACHO team towards the LMC still remains controversial. Low–mass substellar objects and stars with masses larger than ~1 have been ruled out as major components of a MACHO Galactic halo, while stars of half solar masses are the most probable candidates.

Aims. We assess jointly the relative contributions of both red dwarfs and white dwarfs to the mass budget of the Galactic halo.

Methods. We use a Monte Carlo simulator that incorporates up-to-date evolutionary sequences of both red dwarfs and white dwarfs as well as detailed descriptions of both our Galaxy and the LMC. We explore a complete mass range between 0.08 and 1 of possible microlensing candidates and we compare the synthetic populations obtained with our simulator with the results obtained by the MACHO and EROS experiments.

Results. The contribution of the red-dwarf population is insufficient to explain the number of events claimed by the MACHO team; this is even though the optical depth measured for the white-dwarf population alone, increases by a factor of two, after the addition of the red-dwarf population.

Conclusions. We find that the contribution to the halo dark matter of the entire population under study, is smaller than 10%, at the 95% confidence level.