Spectroscopic identification of the optical transient MASTER OT J213908.79+161240.2 and ASASSN-20mf as a dwarf nova
ATel #14042; Keisuke Isogai, Kenta Taguchi, Naoto Kojiguchi, Yusuke Tampo (Kyoto University)
on 26 Sep 2020; 20:34 UT
Credential Certification: Keisuke Isogai (isogai@kusastro.kyoto-u.ac.jp)
Subjects: Optical, Cataclysmic Variable, Transient, Variables
We report on spectra of two large-amplitude optical transients MASTER OT J213908.79+161240.2 = AT 2020ugj and ASASSN-20mf = AT 2020tym.
We obtained the spectra on 2020-09-26.7 UT by using a fiber-fed integral field spectrograph (KOOLS-IFU; Matsubayashi et al. 2019) mounted on the 3.8-m telescope Seimei at Okayama Observatory of Kyoto University.
MASTER OT J213908.79+161240.2 was discovered at 16.1 mag (unfiltered) on 2020-09-26.038 UT by the MASTER team, then rose up to 15.5 mag (ATel #14041). The MASTER team reported that there are no optical counterparts and the limiting magnitude estimated by nearby SDSS objects is r=24.3 mag. However, the data quality in the region is bad, and hence the reported outburst amplitude of >8.8 mag could be overestimated.
We obtained the spectrum of MASTER OT J213908.79+161240.2 on 2020-09-26.688 UT.
Our spectrum shows strong Hα, weak H β, and He II lines.
The large outburst amplitude, blue continuum, and the emission lines suggest that the object is a WZ Sge-type dwarf nova in the early stage.
ASASSN-20mf was discovered at g=14.7 mag on 2020-09-22.440 UT by the ASAS-SN team.
There are no counterparts in VizieR. Thus the outburst amplitude is about 8 mag or more.
We obtained the spectrum of ASASSN-20mf on 2020-09-26.749 UT.
Our spectrum shows strong Hα, and no other clear lines.
The large outburst amplitude, blue continuum, and the emission line suggest that the object is a WZ Sge-type dwarf nova.
Follow-up time-series observations are encouraged.
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