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Stellar Characterization & Variability


Our understanding of exoplanets is directly dependent on our understanding of their host stars.  We measure planetary masses in terms of their host stars’ masses, we infer elemental abundance ratios from those in the atmosphere of their host star, and we infer surface temperatures and conditions informed by their host stars’ luminosities, ages, and activity levels.  We also learn about the planet formation process through statistical comparisons of the properties of planet-hosting stars to those known not to host certain classes of planets.  Host star properties are determined primarily through spectroscopic analysis, and by comparisons with benchmark stars, such as the Sun, and stars in benchmark clusters.

Areas of Specialty

  • Space-based photometry & Astroseismology (Bastien, Gilliland)
  • Stellar magnetic activity (Bastien, Mahadevan)
  • High-resolution stellar spectroscopy (Ramsey, Wright)

Faculty Contacts

  • Fabienne Bastien uses space-based photometry, together with ground-based spectroscopy, to study stellar variability.  Space-based missions like NASA’s Kepler and the upcoming TESS have unveiled a wide variety of stellar behavior which could not be probed from the ground.  Bastien uses data from these missions to study stellar magnetic activity and surface convection (granulation), to measure fundamental stellar properties, and to determine the physical drivers of stellar photometric variability.
  • Ronald Gilliland has been one of the leaders for the Kepler Mission in advocating for inclusion of asteroseismology, then providing support to make this area one of the primary  achievements of the Kepler mission. Stellar astrophysics has seen a revolution over the  past five years as a result of extensive asteroseismology results from Kepler allowing  new and fundamental probes of stellar properties.
  • Suvrath Mahadevan is interested in characterizing the properties of low-mass stars and the implications for planet surveys targeting M stars, such as the Habitable Zone Planet Finger key survey.  Mahadevan is also the leader of a project using the APOGEE spectrograph to observe planet host stars identified by NASA’s Kepler mission.
  • Larry Ramsey is applying his expertise in stellar spectroscopy to the Habitable Zone Planet Finder key survey.
  • Jason Wright and his group members use high resolution spectroscopic analysis an comparisons with benchmark stars, including those in the until-recently-underappreciated old, nearby open cluster Ruprecht 147, to determine properties of exoplanet host stars, including their masses, ages, and compositions.



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