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Studying Semi-Regular Light Variations & Pulsation Periods of Betelgeuse from ~180 years of Photometry: Implications for Evolutionary Changes and for the 2020 Great Dimming

Presentation #141.06 in the session “Stellar Rotation, Variability, and Flares”.

Published onJan 11, 2021
Studying Semi-Regular Light Variations & Pulsation Periods of Betelgeuse from ~180 years of Photometry: Implications for Evolutionary Changes and for the 2020 Great Dimming

Betelgeuse (Alpha Ori; M2-M4 Iab) is the brightest red supergiant and core-collapse supernova progenitor. Dolan et al. 2016 estimates that the star will become a SN II in <10 5 yrs and will be nearly as bright as the full moon. Betelgeuse underwent an unprecedented dimming, reaching V ~ +1.6 mag in Feb-2020 (Guinan et al. 2020). This notorious “Great Dimming” caught the attention of astronomers and the public as a possible harbinger of an impending supernova, but there was no such luck. This surprising behavior stimulated many studies using a wide variety of instruments & techniques covering X-ray to radio wavelengths (see Dupree et al. 2000; Harper et al. 2020, & refs. therein). We report the initial results of the analysis of ~180 yrs of photometry from its discovery in 1839 as semi-regular variable star by Sir John Herschel (1840; 1851). The CLEANest software Period Analysis Software (PERANSO) package (Vanmunster 2014) was primarily used to conduct period (frequency) analyses. The observations typically were binned into 20-40 yr intervals. The observations by Herschel, Argelander, Baxendell and others (Plummer (1911) & Stebbins (1928)) were analyzed. We also studied the visual observations from AAVSO starting in 1919, later adding photoelectric photometry. In addition, we analyzed photoelectric photometry from Wasatonic (1996-2020), including nine years (2003-11) of high-precision space-based SMEI photometry from Joyce et al. 2020. Similar to previous studies of only the AAVSO data (see Kiss et al. 2006), our analyses of all data back to 1837 also indicate two dominant periods of ~5.3–6.1 yrs & ~390-430 days but show a persistent periodicity of 190±18 days. (Joyce et al find P = 185±15d from the SMEI data). These periods are found in most of the data bins. There is evidence the long period P = 5.3 yr (1837–1884) & P = 6.1 yr (2000-2020) & perhaps the 420-d period are increasing. Interestingly our study indicates a possible additive confluence of the light minima from these three periods that occurs near the Great Dimming in February 2020 that may have contributed to the dimming. Upcoming photometry will test this.


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