Visual and Near-Infrared Photometric Observations of Betelgeuse

Volume 50 number 2 (2022)

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Rick Wasatonic

Department of Astrophysics and Planetary Science, Villanova University, Villanova, PA 19085; richard.wasatonic@villanova.edu

Abstract

From 1996 to 2021 time-series photoelectric photometry of the M1-M2Ia-Iab red supergiant Betelgeuse was conducted using a wide-band V-filter centered on λ555 nm and narrow to intermediate-band Wing near infrared (NIR) titanium oxide (TiO) filters centered on λ719 nm, λ754 nm, and λ1024 nm. The observations were made to continually monitor magnitude variations for periodicities and variable amplitudes, calculate seasonal changes of effective temperatures, size, and luminosities, and subsequently examine the interrelationships among these physical properties. Using the V-band observations, short- and long-term dominant periods of 439 ± 5 and 2209 ± 183 days, respectively, were found. Effective temperatures varied from 3528 K to 3731 K, and using an adopted distance of 197 PC, luminosities varied from 70564 Lsun to 114204 Lsun. Using these estimated values of effective temperature and luminosity, calculated radii, assuming spherical symmetry, varied from 710 Rsun to 847 Rsun. NIR to V-band flux ratios indicate that Betelgeuse radiates, on the average, ~10 to ~20 times more in the NIR bands than the visual band. After NIR magnitude conversions from λ1024 nm to λ1040 nm, a surprising result was that the λ754-nm / λ1040-nm flux ratio was nearly 1.0, indicating the bolometric magnitude can be approximated at the shorter wavelength (λ754 nm) magnitude in addition to the theoretically-thought longer (λ1040 nm) wavelength magnitude.