Microlensing events from the 11-year observations of the Wendelstein Calar Alto Pixellensing Project

TL;DR

This study analyzes a decade of M31 microlensing data from the WeCAPP survey, identifying 12 events and characterizing their properties, providing insights into the stellar populations and microlensing phenomena in M31.

Contribution

It presents the longest baseline microlensing survey of M31, with new event detections and detailed analysis of their light curves and properties.

Findings

12 microlensing events identified in M31.

Event timescales range from 0.5 to 14 days.

Lensed stars are likely bright, red, post-main-sequence stars.

Abstract

We present the results of the decade-long M31 observation from the Wendelstein Calar Alto Pixellensing Project (WeCAPP). WeCAPP has monitored M31 from 1997 till 2008 in both R- and I-filters, thus provides the longest baseline of all M31 microlensing surveys. The data are analyzed with the difference imaging analysis, which is most suitable to study variability in crowded stellar fields. We extracted light curves based on each pixel, and devised selection criteria that are optimized to identify microlensing events. This leads to 10 new events, and sums up to a total of 12 microlensing events from WeCAPP, for which we derive their timescales, flux excesses, and colors from their light curves. The color of the lensed stars fall between (R-I) = 0.56 to 1.36, with a median of 1.0 mag, in agreement with our expectation that the sources are most likely bright, red stars at post main-sequence stage. The event FWHM timescales range from 0.5 to 14 days, with a median of 3 days, in good agreement with predictions based on the model of Riffeser et al. (2006).