Is this project an undergraduate, graduate, or faculty project?
Undergraduate
Project Type
group
Campus
Daytona Beach
Authors' Class Standing
Gwynlyn Hannah, Junior Debra Bradfield, Sophomore
Lead Presenter's Name
Gwynlyn Hannah
Lead Presenter's College
DB College of Arts and Sciences
Faculty Mentor Name
Jason P. Aufdenberg
Abstract
The radius of a single star is constrained by a combination of stellar interferometry, which measures the angular size of the star, and the star’s distance, determined from the measured stellar parallax. Many stars hotter than the Sun rapidly rotate and should appear non-circular in the sky. The angular diameters of four stars ( Centauri, Crucis, Sagittarii, and Scorpii) have recently been measured by intensity interferometry using the High Energy Stereoscopic System (H.E.S.S.) at two wavelength bands, 375 nm and 470 nm (Vogel et al. 2025). Two of the stars, Centauri and Crucis, have the same measured angular size in the two bands (within the uncertainties); however, Sagittarii and Scorpii do not. In order to explain this difference, we are developing models that include the effects of rapid rotation, to analyze stellar shapes and constrain fundamental stellar parameters. We will present our latest models for these stars in comparison with interferometric and spectroscopic data. Our models are parameterized by the temperature and gravity at the stellar pole, the fraction of the rotational break-up rate, the inclination of the stellar pole towards Earth, and the position angle of the stellar pole in the sky. We are analyzing how the model visibilities (the interferometric observable) deviate from a circular uniform disk (UD) model. Our models show that in the case of Centauri, model visibility differences for non-circular stars can be up to 20% different from UD estimates, depending on the position angle of the polar axis. Additional position angle analysis will be required to determine how non-circular models appear at different orientations.
Did this research project receive funding support (Spark, SURF, Research Abroad, Student Internal Grants, Collaborative, Climbing, or Ignite Grants) from the Office of Undergraduate Research?
No
Modeling Stellar Interferometry for HESS (High Energy Stereoscopic System) Stars
The radius of a single star is constrained by a combination of stellar interferometry, which measures the angular size of the star, and the star’s distance, determined from the measured stellar parallax. Many stars hotter than the Sun rapidly rotate and should appear non-circular in the sky. The angular diameters of four stars ( Centauri, Crucis, Sagittarii, and Scorpii) have recently been measured by intensity interferometry using the High Energy Stereoscopic System (H.E.S.S.) at two wavelength bands, 375 nm and 470 nm (Vogel et al. 2025). Two of the stars, Centauri and Crucis, have the same measured angular size in the two bands (within the uncertainties); however, Sagittarii and Scorpii do not. In order to explain this difference, we are developing models that include the effects of rapid rotation, to analyze stellar shapes and constrain fundamental stellar parameters. We will present our latest models for these stars in comparison with interferometric and spectroscopic data. Our models are parameterized by the temperature and gravity at the stellar pole, the fraction of the rotational break-up rate, the inclination of the stellar pole towards Earth, and the position angle of the stellar pole in the sky. We are analyzing how the model visibilities (the interferometric observable) deviate from a circular uniform disk (UD) model. Our models show that in the case of Centauri, model visibility differences for non-circular stars can be up to 20% different from UD estimates, depending on the position angle of the polar axis. Additional position angle analysis will be required to determine how non-circular models appear at different orientations.