/pdf/interferometric-astrometric-and-photometric-studies-of-1cgkn5m90u.pdf

Interferometric, Astrometric, and Photometric studies of epsilon Aurigae: Seeing the disk around a distant star.

We present the recent developments preparing the construction of a new visible 6T beam combiner for the CHARA Array, called SPICA. This instrument is designed to achieve a large survey of stellar parameters and to image surface of stars. We first detail the science justification and the general idea governing the establishment of the sample of stars and the main guidance for the optimization of the observations. After a description of the concept of the instrument, we focus our attention on the first important aspect: optimizing and stabilizing the injection of light into single mode fibers in the visible under partial adaptive optics correction. Then we present the main requirements and the preliminary design of a 6T-ABCD integrated optics phase sensor in the H-band to achieve long exposures and reach fainter magnitudes in the visible.

SPICA, a new 6T visible beam combiner for CHARA: science, design and interfaces

The angular size of a star is a critical factor in determining its basic properties1. 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 star2, but only when the photometric uncertainty is smaller than the noise added by atmospheric scintillation3. 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 measurements4. Here we report two occultations of stars observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS)5 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 method6. 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. Using large-aperture Cherenkov telescopes, Benbow et al. have measured the angular sizes of two stars through timely occultations by asteroids, achieving an order of magnitude improvement in resolution over the lunar occultation method.

/pdf/direct-measurement-of-stellar-angular-diameters-by-the-1wdkzu6857.pdf

Direct measurement of stellar angular diameters by the VERITAS Cherenkov telescopes

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 VERITAS Cherenkov telescopes with millisecond sampling, from which we are able to provide a direct measurement of the occulted stars' angular diameter at the $\leq0.1$ milliarcsecond 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.

/pdf/direct-measurement-of-stellar-angular-diameters-by-the-2efwjgnnp4.pdf

Direct measurement of stellar angular diameters by the VERITAS Cherenkov Telescopes

Stellar intensity interferometry (SII) is used to measure the squared visibility, which corresponds to the Fourier transform of the distribution of brightness from a given source for the projected position angle of a pair of telescopes. SII measures the squared visibility through correlations of starlight intensity fluctuations between separated telescope pairs. SII has a significant advantage of being relatively insensitive to atmospheric effects and the minor imperfections of an optical system, allowing for observations over large baselines and low elevation angles, leading to the extension of uv-plane coverage.1 Such uv-plane extension subsequently allows high angular resolution measurements of stellar targets with submilliarcsecond (mas) resolution capabilities. Coincidentally, many telescope arrays constructed to perform gamma-ray observations also meet the requirements of SII. For example, the Very Energetic Radiation Imaging Telescope Array System (VERITAS)2 is an Imaging Air Cherenkov Telescope (IACT) array that is a prime candidate for SII observations.3 Recently, there has been great experimental progress using IACT arrays for SII, as evidenced by successful on-sky observations from VERITAS4,5 and MAGIC.6 Future arrays, such as the Cherenkov Telescope Array (CTA),7 would offer even greater SII capabilities than current observatories due to the increased number of telescopes and larger baselines.8

https://www.spiedigitallibrary.org/journals/Journal-of-Astronomical-Telescopes-Instruments-and-Systems/volume-6/issue-3/037001/ASIIP-a-stellar-intensity-interferometry-target-planner/10.1117/1.JATIS.6.3.037001.pdf

ASIIP: a stellar intensity interferometry target planner

The JMMC Stellar Diameters Catalog v2 (JSDC): A New Release Based on SearchCal Improvements

VizieR Online Data Catalog: JMMC Stellar Diameters Catalogue - JSDC (Lafrasse+, 2010)

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The JMMC Stellar Diameters Catalog v2 (JSDC): A New Release Based on SearchCal Improvements

VizieR Online Data Catalog: JMMC Stellar Diameters Catalogue - JSDC (Lafrasse+, 2010)