ASASSN-21sa: A Deep Dimming Event
ATel #14937; M. Rizzo Smith, K. Z. Stanek, C. S. Kochanek, T. Jayasinghe, D. M. Rowan, C. Christy, T. A. Thompson (OSU), B. J. Shappee (Univ. of Hawaii), T. W.-S. Holoien (Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), Subo Dong (KIAA-PKU), M. Stritzinger (Aarhus)
on 24 Sep 2021; 19:49 UT
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)
Subjects: Optical, Variables
During the ongoing All-Sky Automated Survey for Supernovae (ASAS-SN, Shappee et al. 2014, Kochanek et al. 2017), using data from the quadruple 14-cm ``Cassius'', ``Payne-Gaposchkin'', and ``Paczynski'' telescopes, we identified a star undergoing a deep dimming episode. ASASSN-21sa (Gaia EDR3 source 5940900954032654848 at RA=16:35:45.11, DEC=-48:57:04.30, d~1500 pc, G=11.8 mag, BP-RP=1.3 mag) is luminous and red in Gaia EDR3 catalog (Gaia Collaboration et al., 2021, A&A 649, A1) leading it to be classified as a red giant (R=9.0 R_Sun; L=38.0 L_Sun). It was first observed by ASAS-SN on UT 2016-03-10. Presently, ASASSN-21sa has more than ~2,500 data points.
ASASSN-21sa has a quiescent mean magnitude of g~12.5 (V~12.0). The latest ASAS-SN photometry shows that ASASSN-21sa started to dim around UT 2021-08-24. As of UT 2021-09-24 ASASSN-21sa has faded to g~13.1 and remains faint. In the full ASAS-SN light curve there were no episodes of dimming present in the last ~2000 days.
We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grants GBMF5490 and GBMF10501 to the Ohio State University, NSF grant AST-1908570, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, and the Chinese Academy of Sciences South America Center for Astronomy (CASSACA).