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my CV
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EXOPLANET HOST BINARIES FROM KEPLER & TESS
My postdoc at NASA Ames focuses on understanding how host star multiplicity affect planet formation and survival. We are interested in what binary separations, orbital eccentricities, and mutual inclinations allow planets to form. As part of the speckle group at Ames, I help observe exoplanet host stars with the `Alopeke and Zorro speckle cameras on the Gemini 8m telescopes for the TESS Follow-up Working Group.
My first postdoc project involved collecting all of these observations and determining the orbital separations for exoplanet host stars found to be binaries. We showed that the lack of close companions to exoplanet hosts stars found by past studies is not an observational bias -- exoplanet host binaries have larger separations than field binaries (see figure below), likely because a close companion would disrupt the protoplanetary disk and prevent planets from forming. We also found that TESS cannot detect small, transiting planets in binary systems due to the dilution from the companion. In the righthand figure below, we show the planet radii vs period for single v.s. binary TESS hosts and the clear observational bias against detecting small (<2Re) planets in binary systems. (Read more at Lester et al. 2021)
The second goal of my postdoc project was to measure the visual and spectroscopic orbits of binary stars found to host planets by Kepler, K2, and TESS. We began a monitoring campaign to measure the relative binary positions from speckle interferometry using the Gemini N & S 8m telescopes and the binary radial velocities using echelle spectra from NEID on the WIYN 3.5m and HIRES on the Keck 10m telescopes. So far, we found that the transiting planets' orbits are well aligned with the binary orbits'. You can find the first set of preliminary orbits and details about the orbital alignments in Lester et al. 2023!
Visual Orbits of Spectroscopic Binaries
For my PhD project, I determined the visual and spectroscopic orbits for 8 double-lined spectroscopic binaries by combining echelle spectroscopy from the APO 3.5m and CTIO 1.5m with long baseline interferometry from the CHARA Array.
The fundamental parameters of eclipsing binary stars are used to test stellar evolutionary models by comparing the observed and predicted stellar parameters, such as mass, radius and temperature. However, most eclipsing binaries have short orbital periods, which implies that the stars probably interacted in their early phases and are currently subject to tidal forces. So, it is not clear how applicable the parameters of close binaries are to evolutionary models of single stars. The solution to this problem is to expand binary star studies to longer period systems that are widely separated and not interacting. This requires the measurement of a visual orbit to estimate the orbital inclination, which is then combined with the spectroscopic elements to find masses.
Read more at Lester et al. 2019a, Lester et al. 2019b, Lester et al. 2020, or watch a video of my talk at GRAM 2018.