Measurements of the Size of Betelgeuse Over 15 Years

Details Measurements of the Size of Betelgeuse Over 15 Years Measurements of the Size of Betelgeuse Over 15 Years

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21430901w&link_type=abstract

American Astronomical Society, AAS Meeting #214, #309.01; Bulletin of the American Astronomical Society, Vol. 41, p.738

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Scientific paper

Betelegeuse has one of the largest apparent stellar diameters. It was the first star that was resolved by Michelson and Pease using stellar interferometry and they found a diameter of 0.047 arcsec in the visible band. Betelgeuse has subsequently been a frequent target of stellar interferometers and measurements have shown that the apparent diameter varies as a function of wavelength indicating limb darkening and other effects due to absorption and/or emission by gas and dust surrounding the star.
The Infrared Spatial Interferometer (ISI) has been conducting measurements of Betelgeuse at 11.15 microns wavelength, a wavelength that penetrates dust rather well. The ISI uses a unique heterodyne detection system that combines starlight with CO2 laser local oscillators. The bandwidth is approximately 5.4 GHz and the and the frequency is chosen to avoid absorption or emission lines due to gases. Hence, the radiation measured arises from a stellar "photosphere" defined by the mid-infrared continuum.
The diameter of Betelgeuse has been continuously measured with the same instrumentation over the period 1994 to 2009. During the period 2002-2009 a third telescope was added to the original two providing more baselines and closure phase measurements. Over the measurement period the diameter of Betelguese has diminished from 56 to 47 mas. This data set is, apparently, the longest monitoring of a stellar diameter using consistent instrumentation. The diminishing of the star's size is also compared to the variation in the star's intensity, but a clear correspondence is not seen.
This work was supported by NSF, ONR and the Gordon and Betty Moore Foundation

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