Benjamin Montet

Presenting my work at Cool Stars 19, Uppsala, Sweden. Image Dave Charbonneau.

Long-Term Photometric Variations of Kepler Stars

Kepler has measured short-term variations in the observed flux of hundreds of thousands of stars as a part of its search for exoplanets. During this search, signs of long-term variability in the stars are intentionally destroyed. Full-frame image (FFI) data from Kepler provide an opportunity to recover this variability to better measure long-term photometric variations. In a recent paper, we applied this idea to KIC 8462852, finding it faded by more than 3 percent over the four years of the Kepler mission. We have since released this code as the f3 software package and applied this method to thousands of Sun-like stars, which you can read about in this paper, finding that Sun-like stars with a rotation period shorter than 24 days are more likely to have short-term photometric variations dominated by starspots, while slower rotators are facula-dominated. The data behind this work can be found here. We are extending this project across the main sequence to consider stars of all spectral types observed by Kepler.

Point Spread Function Modeling for K2 and TESS

Nearly all light curves for objects observed by Kepler and K2 are developed through aperture photometry. Inter- and intra-pixel sensitivity variations in the pixel response function (PRF) result in pointing-related systematic effects in the resultant photometry for the K2 mission. Sophisticated methods have been developed to separate astrophysical and instrumental effects, but in crowded fields where aperture photometry fails, these will not produce reliable photometry. I am leading a team to develop PRF-based methods for photometry. for the TESS mission, which will also be applicable to K2. By simultaneously modeling the telescope PRF and the intra-pixel flat field, we can infer stellar brightness variations directly, without needing an additional systematics-correction step. We are developing a suite of open-source tools to produce light curves for every point source observed with TESS at 1% precision or higher, and also plan to use this method to analyze the stellar clusters observed by K2 to search for transiting planets.

Young M Dwarf Binaries

Over the past decade, loose associations of young stars in the solar neighborhood with common ages, kinematics, and origins have been a subject of increasing interest. These young moving groups enable us to test theories of stellar evolution over the first 100 million years of stars' lifetimes. These theories have led to models of young stars, but these models are highly uncertain: different models can predict individual stellar masses that differ by a factor of two or more. To better constrain the low-mass end of these models, we are observing young M dwarf binaries. We have a sample of 60 stars in young, low-mass binary systems for which dynamical masses can be measured on short timescales. By combining astrometric imaging data throughout the orbits of these binary stars with radial velocities, we hope to measure the individual mass of many of these stars to a precision of about 15 percent. I'm working on this project with Brendan Bowler (Texas).