[vsnet-alert 23466] Atel #13010: Low-resolution spectroscopy of the long-orbital period dwarf nova candidate ASASSN-19rx

[Keisuke Isogai]

I posted the following Atel about ASASSN-19rx:
http://www.astronomerstelegram.org/?read=13010

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Low-resolution spectroscopy of the long-orbital period dwarf nova candidate ASASSN-19rx

ATel #13010; Keisuke Isogai, Taichi Kato, Naoto Kojiguchi, Daisaku Nogami, Masaaki Otsuka, Masayuki Yamanaka (Kyoto University)
on 9 Aug 2019; 08:43 UT
Credential Certification: Keisuke Isogai (isogai at kusastro.kyoto-u.ac.jp)

Subjects: Optical, Binary, Cataclysmic Variable, Transient, Variables

ASASSN-19rx was discovered on 2019-07-21.02 UT by the All-Sky Automated Survey
for Supernovae (ASAS-SN; <a href="http://adsabs.harvard.edu/abs/2014ApJ...788...48S">Shappee et al. 2014</a>, <a href="http://adsabs.harvard.edu/abs/2017PASP..129j4502K">Kochanek et al. 2017</a>). Although the ASAS-SN website indicated that this object shows an "unusual slow stellar outburst", we confirmed that its spectrum is a characteristic of a dwarf nova outburst.

The archive data of the ASAS-SN Sky Patrol shows a long (~2 months) and small
(~1 mag) outburst in 2015. In addition, the Gaia color and absolute magnitude
are respectively redder and brighter than those of ordinary dwarf novae.
Thus, it is proposed that this object is a candidate for a long-orbital period
dwarf nova such as V630 Cas or BD Pav (vsnet-alert 23415).
Furthermore, we have found that the object is eclipsing and identified the period of ~2.5 d  (vsnet-alert 23460).
Thus this object is likely to be a kind of such rare objects.

We report on an optical low-resolution spectrum of ASASSN-19rx.
The data was obtained on 2019-07-30.77 UT by fiber-fed integral field spectrograph (KOOLS-IFU; <a href="http://adsabs.harvard.edu/abs/2019arXiv190505430M">Matsubayashi et al. 2019</a>) mounted on the 3.8-m telescope Seimei at Okayama Observatory of Kyoto University.
The obtained spectrum ( http://www.kusastro.kyoto-u.ac.jp/~isogai/atel/asassn-19rx/asassn-19rx_spectrum.png ) shows the Balmer, HeI, HeII and CIII/NIII emission lines.
The emission lines are shifted by +100--200 km/s.
It is remarkable that the HeII 4688 is very strong whereas HeI lines are relatively weak.
Such features are also observed in some other long-orbital period dwarf novae (<a href="http://adsabs.harvard.edu/abs/2018PASJ...70...78K">Kimura et al. 2018</a>).
Although this system should have an accretion disk, all emission lines have single peaked profiles.
We are planning to observe the line-profile variations through the orbital period and outburst cycle.
Observations at other wavelengths are encouraged.