155 research outputs found
Recommended from our members
Pulsating Variable Stars in the MACHO Bulge Database: The Semiregular Variables
We review the pulsating stars contained in the top 24 fields of the MACHO bulge database, with special emphasis on the red semireg-ular stars. Based on period, amplitude and color cuts, we have selected a sample of 2000 semireguku variables with 15 < P < 100 days. Their period-luminosity relation is studied, as well ss their spatial distribution. We find that they follow the bar, unlike the RR Lyrae in these fields
Recommended from our members
Variable Stars in the MACHO Collaboration Database
The MACHO Collaboration`s search for baryonic dark matter via its gravitational microlensing signature has generated a massive database of time ordered photometry of millions Of stars in the LMC and the bulge of the Milky Way. The search`s experimental design and capabilities are reviewed and the dark matter results are briefly noted. Preliminary analysis of the {approximately} 39,000 variable stars discovered in the LMC database is presented and examples of periodic variables are shown. A class of aperiodically variable Be stars is described which is the closest background to microlensing which has been found. Plans for future work on variable stars using the MACHO data are described
Probable Gravitational Microlensing towards the Galatic Bulge
The MACHO project carries out regular photometric monitoring of millions of
stars in the Magellanic Clouds and Galactic Bulge, to search for very rare
gravitational microlensing events due to compact objects in the galactic halo
and disk. A preliminary analysis of one field in the Galactic Bulge, containing
{} stars observed for 190 days, reveals four stars which show
clear evidence for brightenings which are time-symmetric, achromatic in our two
passbands, and have shapes consistent with gravitational microlensing. This is
significantly higher than the event expected from microlensing by
known stars in the disk. If all four events are due to microlensing, a 95\%
confidence lower limit on the optical depth towards our bulge field is , and a ``best fit" value is ,where is the detection efficiency of the
experiment, and . If the true optical depth is close to the
``best fit" value, possible explanations include a ``maximal" disk which
accounts for most of the galactic circular velocity at the solar radius, a halo
which is centrally concentrated, or bulge-bulge microlensing.Comment: submitted to Astrophysical Journal Letters, 10 pages text as
uuencoded compressed PostScript, 5 figures and paper also available via
anonymous ftp from merlin.anu.edu.au in /pub/kcf/mach
- …