Constraining the Inclination Angle of Non-Eclisping Hot Subdwarf + Red Dwarf Binaries using Periodogram Analysis

Most hot subdwarf B (sdB) stars are the descendants of red giants that were stripped of their outer H envelopes due to binary interactions with a companion. Many are formed in tight orbits with red dwarf (dM) or brown dwarf (BD) companions and, with orbital periods on the order of hours, likely formed through common envelope evolution. They can easily be identified photometrically from a strong reflection effect and, occasionally, eclipses. Measuring the distribution of stellar masses in sdB+dM/BD systems may shed light on the effects substellar companions have on stellar evolution, and on the mass-radius relation of hot Jupiters. Some sdB+dM/BD systems, referred to as HW Vir binaries, display primary and secondary eclipses that strongly constrain the inclination and allow masses to be determined through light curve analysis. However, a large fraction of such binaries do not eclipse and only show a reflection effect. We have developed a simple method for constraining the inclination angle in non-eclipsing sdB+dM binaries by using the relative strengths of the fundamental and first harmonic in the Lomb Scargle periodogram. This method proves most useful in datasets with nearly continuous coverage over several orbits. Here we present the details of this approach along with applications to 2-minute cadence data from TESS Cycle 2 and Cycle 3. This material is based in part upon work supported by NASA Award Number 80NSSC19K1720.