Illuminating the Connection Between Young Star Variability and Mass Through PSF Photometry

Aperture photometry is a frequently used method to generate light curves; however, it becomes inaccurate when applied to crowded areas such as young star-forming regions. Point spread function (PSF) photometry offers a solution to this issue by fitting the 3D distribution of the stellar light profile with an effective point-spread function (ePSF) model derived from the data of many stars. PSF photometry allows for neighboring sources as well as background nebulosity to be accounted for, enabling high precision photometric measurements. Using this method, we have created the first PSF light curves for several hundred variable young stellar objects (YSOs) monitored in the 1 million year (Myr) old Lagoon Nebula cluster by the Kepler/K2 mission. From these light curves, physical insights into YSO star-disk systems can be obtained, including the detection of a dependence of variability on stellar mass. We find that higher mass stars (spectral type O through F) in the Lagoon Nebula cluster show fewer indicators of accretion and dust obscuration on month-long timescales, compared to stars with lower mass (spectral type K/M). Numerous other scientific applications of PSF photometry exist, from exoplanet searches to stellar rotation studies. We describe here the process of generating precision photometric time series for Lagoon members, and the science that they are enabling.