On the Microlensing Optical Depth of the Galactic Bar

Astronomy and Astrophysics – Astrophysics

Scientific paper

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

28 pages including 6 postscript figures in uuencoded compressed tar file. Submitted to MNRAS

Scientific paper

The microlensing probability (optical depth $\tau$) toward the Galactic center carries information about the mass distribution of the Galactic bulge/bar, so can be used to constrain the very uncertain shape parameters of the bar. We find $tau$ depends on the bar mass, radial profile, angle, axis scale lengths and boxyness by a few simple analytical formulae, which shows: (1) $\tau$ is proportional to the mass of the bar, $M$. (2) $\tau$ falls along the minor axis with a strong gradient. (3) An oblate bulge can have more optical depth than a triaxial bar if the bar angle $\alpha>45$ degress. (4) $\tau$ is the largest if the angle $\alpha$ and the axis ratio $y_0/x_0$ conspires so that $y_0/x_0=\tan \alpha$. (5) At a fixed field on the minor axis but away from the center, boxy bars with a flat density profile tend to give a larger optical depth than ellipsoidal bars with a steep profile. (6) Main sequence sources should have a significantly lower (20-50\% lower) optical depth than red clump giants if main sequence stars are not observed as deep as the bright clump giants. An application to four COBE-constrained models (Dwek et al. 1994) shows most models produce optical depth $2\sigma$ lower than MACHO and OGLE observed values even with both a massive bar $2.8\times 10^{10} M_\odot$ and a full disk. The high $\tau$ argues for a massive ($> 2\times 10^{10}M_\odot$) boxy bar with $y_0/x0\approx \tan\alpha$ and $\alpha<20$ deg and with a flat radial profile up to corotation.

No associations

LandOfFree

Say what you really think

Search LandOfFree.com for scientists and scientific papers. Rate them and share your experience with other people.

Rating

On the Microlensing Optical Depth of the Galactic Bar does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with On the Microlensing Optical Depth of the Galactic Bar, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and On the Microlensing Optical Depth of the Galactic Bar will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFWR-SCP-O-80477

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.