Observations from Australasia using the Gravitational Microlensing Technique

Philip Yock
, PASA, 17 (1), 35.
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Galactic Bar

The OGLE and MACHO groups included the Galactic bulge in their original targets for gravitational microlensing. Both groups reported a significantly higher event rate for microlensing than was expected (Udalski et al. 1994; Alcock et al. 1995). The high rate can be explained by assuming the Galactic bulge is bar shaped (Zhao, Rich & Spergel 1996). In this model, stars from the near side of the bar lens stars from the far side. Supporting evidence for the model was obtained by the OGLE group who observed a systematic trend in the apparent magnitudes of red clump stars across the bulge (Stanek et al. 1997). These authors found that the microlensing and red clump data can be jointly fitted by a bar inclined at

$20^{\circ}-30^{\circ}$ to our line of sight. These results are consistent with earlier hints of a barred structure (e.g. Blitz & Spergel 1991).

Figure 4: Spectral observations of event MACHO-1995-BLG-30 plotted on the source plane. The relative sizes of the star (solid circle) and the lens's Einstein radius (dotted circle) are plotted to scale, in units of RE. The solid points show the position of the lens at the times when spectra were taken. The observatories where the spectra were taken are indicated by tick marks.
\begin{figure} \begin{center} \psfig{file=fig4.ps,height=7cm} \end{center} \end{figure}

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