The Fainting of the Nearby Red Supergiant Betelgeuse

ATel #13341; E, F. Guinan, R. J. Wasatonic (Villanova Univ.) and T. J. Calderwood (AAVSO)
on 8 Dec 2019; 03:57 UT
Credential Certification: Edward Guinan (edward.guinan@villanova.edu)

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V-band and Wing TiO-band and Near-IR photometry of the semi-regular variable red supergiant, Betelgeuse (alpha Ori; M1.5 - M2.5 Iab) has been carried out over last 25+ years. This photometry was joined by complementary B & V photometry from T. Calderwood (AAVSO). Betelgeuse and Antares are the two nearest red supergiant core-collapse Type-II supernova (SN II) progenitors. Photometry from this season shows the star has been declining in brightness since October 2019, now reaching a modern all-time low of V = +1.12 mag on 07 December 2019 UT. Betelgeuse undergoes complicated quasi-periodic brightness variations with a dominant period of ~420 +/-15 days. But also Betelgeuse has longer-term (5 - 6 years) and shorter term (100 - 180 days) smaller brightness changes. Currently this is the faintest the star has been during our 25+ years of continuous monitoring and 50 years of photoelectric V-band observations. The light variations are complicated and arise from pulsations as well from the waxing and waning of large super-granules on the star's convective surface. Measures of Wing TiO-band (705 nm) and near-IR colors indicate that currently Betelgeuse has relatively strong TiO-bands and has a corresponding lower photospheric temperature of T~3580 K (relative to T~ 3660 K near maximum brightness- typically V ~ 0.2-0.3 mag). This is an opportune time to secure photometry, spectroscopy, spectropolarimetry and if possible interferometry and Adaptive Optics(AO) imaging. Betelgeuse is being frequently monitored during 2019/20 with HST by Andrea Dupree (CfA) as the leading part of the 2019/20 CfA MOB program (the.mob@cfa.harvard).

This ATel was originally submitted by the authors and assigned ATel #13337. Due to a database error, the ATel was subsequently overwritten, and another ATel assigned that number, and this ATel was unavailable for 23 hours. It is re-instated here as ATel #13341. The submission timestamp has been preserved. The Editors regret the error and any inconvenience it may have caused.