Citizen ASAS-SN Discovery of a Likely RCB Variable ASASSN-V J024731.89+635437.9
ATel #14904; C. T. Christy, T. Jayasinghe, K. Z. Stanek, C. S. Kochanek, T. A. Thompson (OSU), M. Wheat, A Sainio (Citizen ASAS-SN), 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 8 Sep 2021; 14:43 UT
Credential Certification: Tharindu Jayasinghe (jayasinghearachchilage.1@osu.edu)
Subjects: Optical, Star, Variables
As part of an ongoing effort by the ASAS-SN project (Shappee et al. 2014, Kochanek et al. 2017), to characterize and catalog bright variable stars using the citizen science project "Citizen ASAS-SN", we report the discovery of a candidate R Coronae Borealis (RCB) variable.
ASASSN-V J024731.89+635437.9 (RAJ2000=02:47:31.89, DEJ2000=63:54:37.9, d~5.0 kpc, Teff~3390 K, BP-RP~3.8 mag, G~12.2, EDR3 source_id=467741901542404736) was classified as an SR variable in the ASAS-SN catalog of variable stars (Jayasinghe et al. 2018-2020). Presently, ASASSN-V J024731.89+635437.9 has more than ~3200 V-band and g-band data points. This system had a quiescent mean magnitude of g~16.1 on UT 2019-10-22. The star dimmed to g~17.1 by UT 2019-11-25 and is currently at g~16.7 as of UT 2021-9-7.
Its unusual g band variability was reported to the ASAS-SN team by participants in the Citizen ASAS-SN project. The ASAS-SN Sky Patrol light curve shows a sudden decline of ~1 mag in the g-band in addition to the large amplitude, irregular pulsations that led to its classification as a semi-regular variable. Such large and rapid declines are typical of dust production episodes in RCB stars. This source is also listed as a Galactic carbon star by Alksnis et al. 2001. The last 100 days of ASAS-SN light curve data may be found here.
RCB stars have carbon-rich atmospheres and typically follow a distinct BP-RP versus J-K relationship (see Shields et al. 2018). This system has J-Ks~2.1 and Gaia BP-RP~3.8 (Cutri et al. 2012, Gaia Collaboration et al. 2020). Most known RCBs lie on or above the locus of carbon stars in BP-RP versus J-K. The colors for this system fall within the expected color ranges for typical RCB systems.
Further photometric and spectroscopic observations are encouraged.
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). For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.
