English

Are the Ogle Microlenses in the Galactic Bar?

Astrophysics 2008-12-18 v3

Abstract

The analysis of the first two years of OGLE data revealed 9 microlensing events of the galactic bulge stars, with the characteristic time scales in the range 8.6<t0<62 8.6 < t_0 < 62 days, where t0=RE/V t_0 = R_E / V . The optical depth to microlensing is larger than (3.3±1.2)×106 ( 3.3 \pm 1.2 ) \times 10^{-6}, in excess of current theoretical estimates, indicating a much higher efficiency for microlensing by either bulge or disk lenses. We argue that the lenses are likely to be ordinary stars in the galactic bar, which has its long axis elongated towards us. A relation between t0 t_0 and the lens masses remains unknown until a quantitative model of bar microlensing becomes available. At this time we have no evidence that the OGLE events are related to dark matter. The geometry of lens distribution can be determined observationally when the microlensing rate is measured over a larger range of galactic longitudes, like 10o<l<+10o -10^o < l < +10^o , and the relative proper motions of the galactic bulge (bar) stars are measured with the HST.

Keywords

Cite

@article{arxiv.astro-ph/9407010,
  title  = {Are the Ogle Microlenses in the Galactic Bar?},
  author = {B. Paczynski and K. Z. Stanek and A. Udalski and M. Szymanski and J. Kaluzny and M. Kubiak and M. Mateo and W. Krzeminski},
  journal= {arXiv preprint arXiv:astro-ph/9407010},
  year   = {2008}
}

Comments

10 pages, 2 figures, revised version accepted for the publication in ApJL, uses AAS LaTeX aaspp.sty macro, PostScript figures and PostScript version of the paper available through anonymous ftp from astro.princeton.edu, directory stanek/tau, or on request