Spectroscopic classification of ASASSN-19si as a WZ Sge-type dwarf nova
ATel #13034; A. Kawash, E. Aydi, L. Chomiuk, K. Sokolovsky, J. Strader (MSU), K. Z. Stanek, C. S. Kochanek, Z. Way, C. Basinger (OSU), B. J. Shappee (Univ. of Hawaii)
on 16 Aug 2019; 20:40 UT
Credential Certification: Kirill Sokolovsky (kirx@scan.sai.msu.ru)
Subjects: Optical, Cataclysmic Variable, Transient, Variables
The optical transient ASASSN-19si
(AT 2019muu) was discovered by the All-Sky Automated Survey for
Supernovae (ASAS-SN; Shappee et al. 2014, Kochanek et al. 2017)
on 2019-07-25.24 UT. It was later rediscovered by the Gaia
Photometric Science Alerts project
( http://gsaweb.ast.cam.ac.uk/alerts/home )
on 2019-08-05.37 as Gaia19diy (TNS Report No. 43351). This object
lies within the Camera 1 field of the TESS Sector 14 observations.
We obtained a 600 s spectrum of ASASSN-19si using OSMOS mounted
on the MDM 2.4m telescope on 2019-08-08.19. The spectrum shows
broad (FWHM ~2500 km/s) Balmer absorption, with narrow (~400 km/s)
emission superimposed on H-alpha. No other clear emission lines
are observed. We also detect He I absorption lines at 4471
and 5876 A. This spectrum is consistent with a dwarf nova
in outburst.
The transient has no match in VizieR, however inspection of the
PanSTARRS ( http://panstarrs.stsci.edu )
g-band mosaic reveals a g=21.7 +/-0.1 source at the transient
position reported by Gaia. The source is lost in the glare of
the nearby bright red star and is not visible at PanSTARRS images
at bands other than g (hence the source is not listed in
the PanSTARRS catalog). Comparing the progenitor magnitude to
the peak at g=13.2 observed by ASAS-SN the flare amplitude
is 8.5 mag, typical for a WZ Sge-type dwarf nova.
