Spectroscopic Classification of TCP J17242302+3258109 as a Dwarf Nova

ATel #15035; Kenta Taguchi, Keisuke Isogai, Miho Kawabata (Kyoto University), Hiroyuki Maehara (National Astronomical Observatory of Japan)
on 14 Nov 2021; 20:17 UT
Credential Certification: Keisuke Isogai (isogai@kusastro.kyoto-u.ac.jp)

Tweet

We report our spectrum of TCP J17242302+3258109 discovered by Hideo Nishimura. We obtained a low-resolution spectrum from 2021-11-14.3756 UT to 2021-11-14.3886 UT using 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.

As reported to CBAT, this object was discovered by Hideo Nishimura at 13.3 mag (unfiltered) on 2021-11-13.3797. Before the discovery, he had also detected the object at 13.8 mag (unfiltered) on 2021-11-11.391, which is the oldest detection of this transient as far as we know. According to the ASAS-SN light curve, this object was fainter than 16.121 g-mag on 2021-11-10.0391581 and was at 13.038 mag on 2021-11-12.0473. Notably, there are no past such outbursts recorded in the ASAS-SN light curve. Katsumi Yoshimoto reported a more precise position of this object, (17:24:22.92, +32:58:12.5), confirming that the position of this object is identical to that of ZTF19aarpgwg. According to PS1 Mean object catalog, there is a star of g = 21.51, r = 21.37, i = 21.38, and z = 20.91 at that position. NUV = 21.700 is also recorded for this star by GALEX DR5.

Our spectrum is dominated by a blue continuum. Also, the Balmer lines (Hα, Hβ, and Hγ), the He II line (4686 Å), and the Bowen component are detected. While the Hα, He II, and the Bowen component show emission profiles, the Hγ line shows an absorption profile, and the Hβ line does a mixture of a narrower emission component and a broader absorption one. These spectroscopic characteristics and blue progenitor manifest that this object is a dwarf nova. Such a large amplitude (∼ 8.5 g-mags, comparing the PS1 data and ASAS-SN maximum) strongly suggests that this dwarf nova is a WZ Sge-type one.

Our Spectrum