Faculty Mentor

Jason P. Aufdenberg


Since 2020 the Very Energetic Radiation Imaging Telescope Array System (VERITAS) has observed 48 stellar targets using the technique of Stellar Intensity Interferometry (SII). Angular diameter measurements by VERITAS SII (VSII) in a waveband near 400 nm complement existing angular diameter measurements in the near-infrared. VSII observations will test fundamental predictions of stellar atmosphere models and should be more sensitive to limb darkening and gravity darkening effects than measurements in the near-IR, however, the magnitude of this difference has not been systematically explored in the literature. In order to investigate the synthetic interferometric (as well as spectroscopic) appearance of stars in the blue relative to the near-IR, we have computed grids of model atmospheres (3463 models in total) appropriate for six stars observed by VSII: four rapid rotators α Cep, α Leo, α Lyr, and η UMa, along with two slow rotators β UMa and β CMa. This paper presents synthetic spectra, model images, and visibility predictions for these stars and three others (α Aql, α Oph, and β Cas). We predict these stars will appear smaller in angular size and exhibit higher visibilities in the first lobe of the visibility curve at 400 nm relative to 1746 nm at the same spatial frequencies, consistent with our expectations. VSII baselines see only the second and higher lobes of α Lyr and α Aql due to their large angular diameters. α Aql is predicted to have a rich spectrum of visibilities in the third lobe, however, the visibilities are very low. Synthetic spectra match archival spectra around 400nm best for α Leo, α Aql, α Oph, β UMa and β CMa, while for α Cep, β Cas, and α Lyr synthetic spectra exhibit higher fluctuations in line strength than observed. A synthetic spectrum for η UMa provides a good match to the Hδ line, but not for the adjacent He I lines. In addition to resolving the discrepancies between the synthetic and archival spectra, we anticipate comparing our visibility predictions to VSII observations in the near future.



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