M dwarfs are prime targets for finding small transiting exoplanets, since larger planet-to-star mass and radius ratios yield larger transit and radial velocity (RV) signals, respectively. However, the…

This is a $230,326.35 grant awarded by the National Aeronautics and Space Administration (NASA) Shared Services Center to The Pennsylvania State University (Penn State) to conduct research on using single-lined eclipsing binary (SLEB) stars as a way to better understand the physical properties of M dwarf stars. This grant is part of NASA's efforts to improve the accuracy of models for M dwarf interiors and stellar parameters, which are critical for exoplanet discovery and characterization around these stars. The research will involve jointly modeling spectral energy distributions, transit light curves, and radial velocities for 33 SLEB systems to directly measure the masses, radii, and temperatures of the M dwarf components. This will significantly increase the sample of well-characterized single M dwarfs, providing key insights into the discrepancies between empirical measurements and model predictions for these stars. The grant has a period of performance ending on December 13, 2023 and does not have a set-aside designation.

M dwarfs are prime targets for finding small transiting exoplanets, since larger planet-to-star mass and radius ratios yield larger transit and radial velocity (RV) signals, respectively. However, the empirically-determined parameters of many m dwarfs grossly and significantly disagree with the predictions of many stellar models. This may be due to the fact that the majority of precisely measured m dwarf masses and radii come from double-lined eclipsing binary systems (m-m EBS), and we do not yet know the effects that binarity may have on the physical properties of STARS, and therefore on these discrepancies. Moreover, we observe systematic differences in stellar parameters for single m dwarfs versus those in binaries, and the cause of this discrepancy is also unknown. Single-lined eclipsing binaries (slebs) -- namely, those MIS-identified by transit surveys as potential planetary systems -- provide a wider window into the m dwarf parameter discrepancy: not only do slebs increase the number of systems that can be characterized precisely and accurately by an order of magnitude, but they probe regions of m dwarf binary parameter space that are inaccessible via or underpopulated by the handful of well-characterized m-m binaries known today. One can now measure precise and accurate sleb parameters without relying (as extant sleb studies do) on stellar isochrones, empirical relations, or assumptions about tidal synchronicity by jointly modeling the spectral energy distribution (SED, with the ultra-precise gaia parallax), transits (i.e. primary eclipses), and radial velocities (RVS). This method has yet to be adopted by sleb studies in the literature. Additionally, the high-precision, continuous, space-based photometry from tess, kepler/K2, and spitzer reveal periodic out-of-transit variability (ootv) -- ellipsoidal variations, reflected light, and doppler beaming -- that can be analyzed to obtain independent mass, radius, and effective temperature measurements, as well as information about stellar albedos and oblateness. We will analyze 33 sleb light curves for which we have full RV orbits and light curves from tess, kepler/K2, and spitzer. We will jointly model the transits and eclipses, RVS, and seds, including broad-band photometry from NASA observatories, to recover nearly empirical masses, radii, and brightness temperatures for both STARS in these systems. We will also model ootv to provide independent determinations of these quantities. With these results, we will: -assess if and how m dwarfs' radius and temperature discrepancies depend on their orbital configurations and interior structures. -test and refine commonly used analytic ootv models to refine their accuracy and better understand their limitations. -identify extreme mass-ratio sleb candidates in tess data and use our aforementioned analyses, to identify the most interesting candidates for future follow-up observations and characterization. Our program will produce the largest sample of slebs with stellar parameters determined to high accuracy and precision without isochrones or empirical relations. We will increase the number of m dwarfs with well- and directly determined masses and radii (i.e. those in m-m EBS) by 50%. More significantly, we will increase the number of such m dwarfs on long periods -- where the effects of binary interactions on measured stellar properties should be minimal -- by an order of magnitude. Ultimately, our study will yield a deeper understanding of missing physics in the models of m dwarf interiors and binary phase curve variations.