Spectroscopic classification of AT2020vak and ZTF20acjpwas/AT2020wup
ATel #14109; Monika Soraisam (NCSA/UIUC), Kevin McKinnon, Rafael Nunez, Stephanie Figuereo, Puragra Guhathakurta (UCSC), Chien-Hsiu Lee (NOIR Lab), Sarah DeSantis (Steward), Tim Marquez (UCSB), Mi Zhang, Xing Gao (Xingming Observatory)
on 21 Oct 2020; 23:07 UT
Credential Certification: Monika Soraisam (soraisam@illinois.edu)
Subjects: Optical, Cataclysmic Variable, Star, Transient, Variables
We report the spectroscopic observations of AT2020vak (RA 0h42m49.62s, DEC +41d16m52.10s) and ZTF20acjpwas/AT2020wup (RA 7h35m35.57s, DEC +2d7m9.72s) from the SALVATION project (ATel #13952). AT2020vak was reported as a possible nova candidate in M31 via TNS (https://wis-tns.weizmann.ac.il/object/2020vak), while AT2020wup was flagged by a filter on the ANTARES alert-broker (https://antares.noirlab.edu/loci/ANT2020aeihd7i) customized to find promising stellar explosive events from the ZTF public alert stream.
On 2020 Oct 19 UT, we obtained the spectra of these two sources with the Kast double spectrograph on the Shane 3-m telescope at Lick Observatory. The spectrum of AT2020wup shows a blue continuum with Balmer as well as HeI 4471 and 5875 Å lines in absorption, supporting its photometric classification as a (WZ Sge-type) dwarf nova reported in vsnet-alert #24817 (https://www.aavso.org/vsx/index.php?view=detail.top&oid=2213772).
The spectrum of AT2020vak shows absorption lines of various elements including Balmer lines, CaII, G-band, and many metals pointing to an F-type stellar spectrum. The lines are blue-shifted, with the radial velocity (based on H-beta) around -500 km/s, and fitting a simple blackbody model to the spectrum gives a temperature of around 6700 K. Some of the authors here (MZ, XG) have been performing photometric follow-up of the source, which preliminarily shows an increase in brightness by more than 3 mag over 10 days, unusual for an F-type star. This source is located within 2 arcsec of the planetary nebula Ford M31 330.
