The contribution of Oxygen--Neon white dwarfs to the MACHO content of the Galactic Halo

CAMACHO, J.; TORRES, S.; ISERN, J.; ALTHAUS, L. G.; GARCIA-BERRO, E.

ASTRONOMY AND ASTROPHYSICS

EDP Sciences

Año: 2007 vol. 471 p. 151 - 158

0004-6361

The interpretation of microlensing results towards the LargeMagellanic  Cloud  (LMC)  still  remains controversial.  Whitedwarfs  have been  proposed to  explain these  results and,  hence, tocontribute significantly to  the mass budget of our  Galaxy. However, several  constraints  on  the  role  played white dwarfs still exist.Massive white  dwarfs are thought to  be made of a  mixture of oxygenand neon. Correspondingly, their cooling  rate is larger than those oftypical carbon--oxygen  white dwarfs and they fade  to invisibility inshort timescales.  Consequently, they  constitute a good candidate forexplaining the microlensing results. Here, we examine in detail thishypothesis by  using the most  recent and up--to--date  cooling tracksfor massive white dwarfs and  a Monte Carlo simulator which takes into account   the  most   relevant  Galactic   inputs. We find  thatoxygen--neon  (ONe)  white dwarfs  cannot  account  for a  substantialfraction of  the microlensing depth towards the  LMC, independently ofthe adopted  initial mass function, although  some microlensing eventscould  be  due  to  ONe  white  dwarfs. The  white  dwarf  populationcontributes at most a 5\% to the mass of the Galactic halo