UV photometry of 548 variables stars in M31

Field 2, which is 6.4kpc in diameter at the distance of M31, includes a substantial part of the NE spiral arms of the galaxy. We have obtained a second observation of Field 2 with the far-ultraviolet (FUV) F148W (148nm) filter, separated from the first observation by 1465 days.

Both observations are analyzed to detect sources that are variable at a >3{sigma} confidence level. For sources with less than ~2" separation, we apply multi-Gaussian fits, to obtain reliable magnitudes in the presence of source crowding. The variable sources are found to be concentrated in the spiral arms, with fraction of variable to nonvariable sources ~2 times higher than for interarm regions, indicating an association of FUV variables with young stellar populations.