ASAS-SN Discovery of a Rapid and Deep Fading Episode in a YSO Candidate

ATel #13818; Z. Way, K. Z. Stanek, T. Jayasinghe, C. S. Kochanek, C. Basinger, 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 19 Jun 2020; 20:14 UT
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)

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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 ``Brutus'', ``Cassius'', ``Payne-Gaposchkin'', ``Leavitt'', and ``Paczynski'' telescopes, we identified a young stellar source undergoing an unusual dimming episode. The source ASASSN-V J181654.06-202117.6 (position from Gaia DR2, source_id=4094361919233083520, d=1.3 kpc, L = 13.7 L_sun, Teff=6145 K) was first observed by ASAS-SN on UT 2015-02-24. The line of sight extinction from the Bayestar19 dust maps (Green et al. 2019) to ASASSN-V J181654.06-202117.6 is significant (A_V~1.3 mag, A_g~1.5 mag) as it is located in the Galactic disk with (l,b)~(10.972,-1.911). Presently, ASASSN-V J181654.06-202117.6 has more than ~1680 ASAS-SN epochs.

The source ASASSN-V J181654.06-202117.6 has a quiescent mean magnitude of g~12.8 (V~12.5). The latest ASAS-SN photometry shows that ASASSN-V J181654.06-202117.6 faded from g~12.8 on UT 2020-06-03.4, to g~13.5 on 2020-06-19.5. This source is not significantly variable in the ASAS-SN V/g-band data over the previous ~1940 days. There are no matches to known variables in Vizier or the AAVSO VSX catalog, and the star is not significantly variable in the CRTS or ASAS data, going back to 2001. However, it has been classified as a Class I/II YSO candidate by Marton et al. (2016) using the AllWISE catalog.

Follow-up observations of this interesting object are strongly 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 grant GBMF5490 to the Ohio State University, NSF grant AST-1515927, 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.