More Like this

1. An Angular Diameter Measurement of β UMa via Stellar Intensity Interferometry with the VERITAS Observatory

   https://doi.org/10.3847/1538-4357/ad2b68  

   Acharyya, A; Aufdenberg, J P; Bangale, P; Bartkoske, J T; Batista, P; Benbow, W; Chromey, A J; Davis, J D; Feng, Q; Foote, G M; et al (April 2024, The Astrophysical Journal)

   Abstract We use the Very Energetic Radiation Imaging telescope Array System (VERITAS) imaging air Cherenkov telescope array to obtain the first measured angular diameter ofβUMa at visual wavelengths using stellar intensity interferometry (SII) and independently constrain the limb-darkened angular diameter. The age of the Ursa Major moving group has been assessed from the ages of its members, including nuclear member Merak (βUMa), an A1-type subgiant, by comparing effective temperature and luminosity constraints to model stellar evolution tracks. Previous interferometric limb-darkened angular-diameter measurements ofβUMa in the near-infrared (Center for High Angular Resolution Astronomy (CHARA) Array, 1.149 ± 0.014 mas) and mid-infrared (Keck Nuller, 1.08 ± 0.07 mas), together with the measured parallax and bolometric flux, have constrained the effective temperature. This paper presents current VERITAS-SII observation and analysis procedures to derive squared visibilities from correlation functions. We fit the resulting squared visibilities to find a limb-darkened angular diameter of 1.07 ± 0.04 (stat) ± 0.05 (sys) mas, using synthetic visibilities from a stellar atmosphere model that provides a good match to the spectrum ofβUMa in the optical wave band. The VERITAS-SII limb-darkened angular diameter yields an effective temperature of 9700 ± 200 ± 200 K, consistent with ultraviolet spectrophotometry, and an age of 390 ± 29 ± 32 Myr, using MESA Isochrones and Stellar Tracks. This age is consistent with 408 ± 6 Myr from the CHARA Array angular diameter. 

   more » « less
2. Resolving the Binary System Spica using the VERITAS Stellar Intensity Interferometer

   Breeland-Newcomb, Katie; Kieda, David; Davis, Jonathan (January 2023, American Astronomical Society meeting)

   AB In 2019, the Very Energetic Radiation Imaging Telescope Array System (VERITAS) was augmented with high-speed optical electronics in order to allow for Stellar Intensity Interferometry (SII) observational capabilities. This research shows how VERITAS-SII (VSII), which measures correlations of starlight intensity fluctuations across spatially separated telescopes, can enable the characterization of binary stellar systems. We first use VSII data collected on the binary star Spica to develop a dynamic analysis technique. We then simulate the squared visibility curve given a particular orientation of Spica's components. Because of Spica's 4.0145-day period, the binary separation and orientation, and therefore the simulated squared visibility, should vary greatly from night to night. These variations are consistent with measured variations in the observed squared visibility curves. The initial results indicate that VSII observations potentially demonstrate good sensitivity to the evolution of the Spica binary system. With further development, it may be possible to fit a multi-dimensional image to the system, opening the door to model-dependent VSII imaging. 

   more » « less
3. Demonstration of stellar intensity interferometry with the four VERITAS telescopes

   https://doi.org/10.1038/s41550-020-1143-y  

   Abeysekara, A. U.; Benbow, W.; Brill, A.; Buckley, J. H.; Christiansen, J. L.; Chromey, A. J.; Daniel, M. K.; Davis, J.; Falcone, A.; Feng, Q.; et al (July 2020, Nature Astronomy)

   High angular resolution observations at optical wavelengths provide valuable insights into stellar astrophysics, and enable direct measurements of fundamental stellar parameters and the probing of stellar atmospheres, circumstellar disks, the elongation of rapidly rotating stars and the pulsations of Cepheid variable stars. The angular size of most stars is of the order of one milliarcsecond or less, and to spatially resolve stellar disks and features at this scale requires an optical interferometer using an array of telescopes with baselines on the order of hundreds of metres. We report on the implementation of a stellar intensity interferometry system developed for the four VERITAS imaging atmospheric Cherenkov telescopes. The system was used to measure the angular diameter of the two sub-milliarcsecond stars β Canis Majoris and ϵ Orionis with a precision of greater than 5%. The system uses an offline approach in which starlight intensity fluctuations that are recorded at each telescope are correlated post observation. The technique can be readily scaled onto tens to hundreds of telescopes, providing a capability that has proven technically challenging to the current generation of optical amplitude interferometry observatories. This work demonstrates the feasibility of performing astrophysical measurements using imaging atmospheric Cherenkov telescope arrays as intensity interferometers and shows the promise for integrating an intensity interferometry system within future observatories such as the Cherenkov Telescope Array. 

   more » « less
4. Implementation of an intensity interferometry system on the StarBase observatory

   https://doi.org/10.1117/12.2312716  

   Matthews, Nolan; Kieda, David B.; Snow, Shaun; LeBohec, Stephan; Clarke, Orville; Mérand, Antoine; Creech-Eakman, Michelle J.; Tuthill, Peter G. (July 2018, Proc. SPIE 10701 Optical and Infrared Interferometry and Imaging IV)

   A modern implementation of a stellar intensity interferometry (SII) system on an array of large optical telescopes would be a highly valuable complement to the current generation of optical amplitude interferometers. The SII technique allows for observations at short optical wavelengths (U/B/V bands) with potentially dense (u,v) plane coverage. We describe a complete SII system that is used to measure the spatial coherence of a laboratory source which exhibits signal to noise ratios comparable to actual stellar sources. A novel analysis method, based on the correlation measurements between orthogonal polarization states, was developed to remove unwanted effects of spurious correlations. Our system is currently being tested in night sky observations at the StarBase Observatory (Grantsville, Utah) and will soon be ported to the VERITAS (Amado, AZ) telescopes. The system can readily be integrated with current optical telescopes at minimal cost. The work here serves as a technological pathfinder for implementing SII on the future Cherenkov Telescope Array. 

   more » « less
5. Direct measurement of stellar angular diameters by the VERITAS Cherenkov telescopes

   https://doi.org/10.1038/s41550-019-0741-z  

   Benbow, W.; Bird, R.; Brill, A.; Brose, R.; Chromey, A. J.; Daniel, M. K.; Feng, Q.; Finley, J. P.; Fortson, L.; Furniss, A.; et al (April 2019, Nature Astronomy)

   The angular size of a star is a critical factor in determining its basic properties. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by studying the diffraction pattern in the shadow cast when an asteroid occults a star, but only when the photometric uncertainty is smaller than the noise added by atmospheric scintillation. Atmospheric Cherenkov telescopes used for particle astrophysics observations have not generally been exploited for optical astronomy due to the modest optical quality of the mirror surface. However, their large mirror area makes them well suited for such high-time-resolution precision photometry measurements. Here we report two occultations of stars observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) Cherenkov telescopes with millisecond sampling, from which we are able to provide a direct measurement of the occulted stars’ angular diameter at the ≤0.1 mas scale. This is a resolution never achieved before with optical measurements and represents an order of magnitude improvement over the equivalent lunar occultation method. We compare the resulting stellar radius with empirically derived estimates from temperature and brightness measurements, confirming the latter can be biased for stars with ambiguous stellar classifications. 

   more » « less