Spectroscopic confirmation of recent brightening of GDS J1830235-135539 as a symbiotic nova and ASASSN-22lk as a large-amplitude dwarf nova

ATel #15623; Kenta Taguchi (Kyoto University), Minoru Yamamoto, Masayuki Moriyama (VSOLJ), Taichi Kato, Keisuke Isogai, Naoto Kojiguchi, Yusuke Tampo (Kyoto University)
on 23 Sep 2022; 16:25 UT
Credential Certification: Keisuke Isogai (isogai@kusastro.kyoto-u.ac.jp)

Tweet

We report our low-resolution spectra of GDS J1830235-135539 and ASASSN-22lk obtained by the fiber-fed integral field spectrograph (KOOLS-IFU; Matsubayashi et al. 2019) mounted on the 3.8 m Seimei telescope (Kurita et al. 2020) at Okayama Observatory of Kyoto University.

Minoru Yamamoto discovered a slowly brightening object and reported it to a mailing list run by the Variable Star Observers' League in Japan (VSOLJ). The position is identical to that of a known variable star GDS J1830235-135539 discovered by the Bochum Galactic Disk Survey (GDS, Hackstein et al. 2015). According to the OGLE Collection of Variable Stars (Udalski et al. 2015, Iwanek et al. 2022) and Gaia DR3 (Gaia Collaboration 2022), it is a Mira variable. We show the multicolor light curves by the All-Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014, Kochanek et al. 2017), Asteroid Terrestrial-impact Last Alert System (ATLAS, Tonry et al. 2018, Smith et al. 2020, Heinze et al. 2018), OGLE, GDS, and us. In both the amplitude and timescale, the current slow brightening goes beyond the past variation as a Mira. To identify the nature of the current brightening, we took the above spectrum from 2022-09-20.4300 UT to 2022-09-20.4318 UT (3 times of 1 min exposure). It shows red continuum and emission lines of Hα, Hβ, Hγ, He_I, O_I, and Fe_II. By the variability above and our spectrum, we conclude it is a symbiotic nova containing a Mira.

We also observed ASASSN-22lk using the same instrument in the same settings from 2022-09-20.4373 UT to 2022-09-20.4390 UT. Our spectrum is dominated by a blue continuum. Absorption lines of Hβ, Hγ, and Hδ are detected. The absorption feature of Hα is very weak. We conclude it is a dwarf nova with a high amplitude (according to ASAS-SN, more than eight magnitudes).