Characterizing exoplanet host stars

The parent star in any exoplanet system dominates the system in every respect: it comprises most of the mass and represents the principal energy source. For most exoplanets, the only light observed is that emitted by the star. This light is then modified by the influence of the exoplanet through, for instance, occultation or Doppler shifting.

Planetary parameters -- including mass, radius, radiation environment, and equilibrium temperature -- are inferred from the measured stellar parameters. The team will use Georgia State University’s CHARA (Center for High Angular Resolution Astronomy) Array, the longest baseline optical/infrared interferometer in the world, to study exoplanet host stars.

They will determine astrophysical parameters, including empirical values for the system parameters such as planetary radius for transiting systems, and calculated parameters such as the boundaries of the system habitable zone (HZ). The team will also use their interferometric observations to determine radii for stars with and without planets. This project will support a graduate student’s thesis research, as well as enable research experiences for several undergraduate students at LSU.

The proposal team will maintain a public presence by giving talks open to the community and through collaboration with dozens of amateurs from the American Association of Variable Star Observers. They will maintain an online presence through their education program hosted on Reddit and communication through various other media channels.

The researdh team will directly determine physical radii and effective temperatures of a large number of nearby stars with a special emphasis on exoplanet hosts. The high angular resolution attainable via long-baseline optical interferometry (LBOI) is routinely used to directly measure the angular sizes of such nearby targets. Combining angular sizes from LBOI, trigonometric parallaxes from Hipparcos, and bolometric fluxes via photometry and spectral energy distribution fitting allows for largely model-independent determinations of stellar radii and effective temperatures.

Atmospheric properties for interferometry targets are also possible to measure as they are nearby and very bright, thus allowing for high signal-to-noise observations. The same data serve to establish semi-empirical, predictive relations that tie stellar observables to fundamental properties, such as surface brightness relations, which relate stellar broad band color to angular radius.

The team will continue their interferometric survey of nearby dwarf stars with an emphasis on exoplanet host stars. Their aim will be to establish direct and indirect characterizations of all applicable exoplanetary systems. Data from this program provide empirical system parameters where applicable and improve the predictive accuracy of stellar models and parameter relations for the characterization of exoplanetary systems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.