ASASSN-25db: A Deep Ongoing Dimming Event
ATel #17304; D. M. Rowan, K. Z. Stanek, C. S. Kochanek, B. JoHantgen, J. Callahan, S. A. Petz (OSU), H. Barker (Rutherford Street Observatory), B. J. Shappee (Univ. of Hawaii)
on 24 Jul 2025; 14:13 UT
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)
Subjects: Optical, Variables
Using data from the All-Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014, Kochanek et al. 2017, Hart et al. 2023 ), we identified a star with a deep, ongoing, dimming event. ASASSN-25db (RA = 17h18m33.14s, DEC = -32d06m30.96s, G = 12.7, BP = 13.1, RP =11.5, DR3 source_id = 5979603728993854720 is a red giant star with a Gaia DR3 (Gaia Collaboration et al. 2023 ) extinction-corrected absolute magnitude M_G = 3.2 mag and color GBP -GRP = 1.3 mag, but we note that the fractional Gaia parallax uncertainty is large (~40%).
This star was first observed by ASAS-SN on UT 2016-03-09 and it has roughly ~ 5,700 data points at this time. It had a mean g-magnitude of ~13.0 (V ~ 12.7) and no previous dimming events. The dimming event began around UT 2025-05-20. The star faded by about 0.75 mag in the g-band and began to brighten again on UT 2025-07-17. An R ~ 1000 spectrum taken with a 250mm Newtonian and Shelyak LISA spectrograph on UT 2025-07-20 shows Na D absorption and H-alpha emission. There is also an apparent infrared excess in the WISE W3 and W4 bands (Cutri et al. 2021).
We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN operations are funded in part by the Gordon and Betty Moore Foundation through grants GBMF5490 and GBMF10501 to the Ohio State University, and Alfred P. Sloan Foundation grant G-2021-14192.
