LEAPS-MPS: Constraining Stellar Structure and Evolution of Massive Stars with Optical Interferometry

Massive stars, specifically O and B-stars, are rare and short lived. Nevertheless, they dominate the luminosity and chemical evolution of galaxies, and energize the intergalactic medium. It is thus important to understand their structure and evolution.

This can be done by determining their positions on a plot of luminosity and effective temperature (Teff) - i.e., an Hertzprung-Russell (HR) diagram - relative to theoretical evolutionary "tracks" that stars of a given mass will follow over their lifetime. Ordinarily, Teff is difficult to measure for massive stars and one must rely on estimates from stellar atmosphere models.

The Principal Investigator (PI) of this project and her students will derive Teff directly using measured stellar luminosities and diameters, with the latter obtained using long baseline optical interferometric observations with the Center for High Angular Resolution Astronomy (CHARA) array. All in all, direct determinations of Teff for forty-one targets (11 O-stars and 30 B-stars) will be carried out by the team, allowing precise constraints for key stellar parameters as well as an assessment of estimates based on stellar atmosphere models.

Two side projects will explore the effects of stellar winds and measure the shape of the rapidly rotating star zeta Oph. The award will also allow the university to join the Southeastern Association for Research in Astronomy (SARA) consortium, providing access to a global network of robotic telescopes. This award will support a year-round research experience for an undergraduate student including travel to CHARA workshops and winter AAS meetings.

Long baseline optical interferometry will allow the PI and students to derive key stellar parameters with unprecedented precision. The CHARA array is currently the only interferometer in the world capable of attaining sufficiently high angular resolution to resolve the disks of distant O and B- stars. Together with precise stellar distances provided by the recent Gaia mission, the team will use measured angular diameters to calculate accurate stellar radii.

These will be combined with calibrated spectrophotometry to calculate accurate Teff. The research program outlined in this proposal seeks to provide a robust test of stellar atmospheric models with precise, observationally determined parameters for a statistically significant sample of O and B-stars. This work will further result in the creation of a low resolution optical spectral library for massive stars, as there is historically not a large amount of data in this area.

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.