A Puzzle Involving Galactic Bulge Microlensing Events

TL;DR

This study finds a strong correlation between microlensing magnification and metallicity in bulge stars, raising questions about potential sample bias and emphasizing the need for further observations to accurately determine the bulge's metallicity distribution.

Contribution

It reveals a significant correlation between microlensing magnification and stellar metallicity, challenging existing assumptions and highlighting the need for additional data to understand this bias.

Findings

Strong correlation between magnification and [Fe/H]

Sample bias likely influences observed metallicities

Further observations needed for accurate metallicity distribution

Abstract

We study a sample of 16 microlensed Galactic bulge main sequence turnoff region stars for which high dispersion spectra have been obtained with detailed abundance analyses. We demonstrate that there is a very strong and highly statistically significant correlation between the maximum magnification of the microlensed bulge star and the value of the [Fe/H] deduced from the high resolution spectrum of each object. Physics demands that this correlation, assuming it to be real, be the result of some sample bias. We suggest several possible explanations, but are forced to reject them all,and are left puzzled. To obtain a reliable metallicity distribution in the Galactic bulge based on microlensed dwarf stars it will be necessary to resolve this issue through the course of additional observations.