SALT spectroscopic follow-up of the unusual variable ASASSN-20da
ATel #13573; E. Aydi (MSU), D. A. H. Buckley (SAAO), L. Chomiuk, A. Kawash K. V. Sokolovsky, J. Strader (MSU), M. Orio (UoW, INAF), Z. S. Way, K. Z. Stanek, C. S. Kochanek (OSU), B. J. Shappee (Univ. of Hawaii)
on 21 Mar 2020; 10:26 UT
Credential Certification: Elias Aydi (eaydi@saao.ac.za)
Subjects: Optical, Star, Transient, Variables
Referred to by ATel #: 14593
We report on high-resolution optical spectroscopy of the unusual variable ASASSN-20da, which was reported by the All-Sky Automated Survey for SNe (ASAS-SN, Shappee et al. 2014, ApJ, 788, 48) on 2020-03-13.
The system matches Gaia DR2 source (ID #5848963158970287616), with G = 12.3 at a distance ~ 630 parsec, and it is probably an F-type main-sequence star. Based on the ASAS-SN data, the source did not show any previous significant variability from 2016-03-10 until 2020-03-08, when the source began to brighten with unusual brightness oscillations of increasing amplitude on a timescale of less than a day. The g-band flux peaked on 2020-03-13 at g = 11.9, but it is still showing brightness oscillations.
On 2020-03-18.94UT we obtained a 1500 s spectrum using the High Resolution Spectrograph (HRS; Crause et al. 2014, Proc. SPIE, 91476) mounted on the 11m Southern African Large Telescope as part of the SALT Large Science Program on Transients. The observations were taken in the LR mode of HRS which covers the spectral range of 3800-8900 A at a resolution of R=14000. The data were reduced with the SALT HRS MIDAS pipeline (Kniazev et al. 2016, MNRAS 459, 3068).
The spectrum shows Balmer, O I (7773 and 8446 A), and Ca II absorption lines. The Balmer lines have a FWHM of around 250 km/s but the base of the lines is characterized by a FWZI of around 2000 km/s. The nature of the variability/brightening is still unclear. Further follow up are strongly encouraged.
The latest ASAS-SN light curve: https://asas-sn.osu.edu/light_curves/1202dde4-47ec-4220-998e-de7a0410262a
