Classification of ASASSN-18ix as a dwarf nova
ATel #11607; E. Aydi (South African Astronomical Observatory, University of Cape Town), D. A. H. Buckley (SAAO), S. Mohamed (SAAO, UCT), P. A. Whitelock (SAAO, UCT), L. Chomiuk, J. Strader (MSU), K. Z. Stanek (OSU)
on 4 May 2018; 13:51 UT
Credential Certification: David Buckley (dibnob@saao.ac.za)
Subjects: Optical, Transient
We report on SALT high-resolution spectroscopy of ASASSN-18ix which was reported as a possible Galactic nova by K. Z. Stanek et al. (ATel #11561).
We obtained a 2000 s spectrum of this object under the SALT Large Science Program on transients on 2018 April 24.99 (HJD 2458233.50), using the High Resolution Spectrograph (HRS; Crause et al. 2014, Proc. SPIE, 91476) on the Southern African Large Telescope (SALT). Observations were taken in the Low Resolution (LR) mode of HRS, covering a spectral range of 3800-8900 Å at a resolution of R = 14,000. The data were reduced with the SALT HRS MIDAS pipeline (Kniazev et al. 2016, MNRAS 459, 3068).
The spectrum is dominated by weak emission lines of H I and He I (see below a full list of the line identification) superimposed on broad absorption lines, typical of dwarf novae on decline. The emission lines are characterized by a double peaked profiles, typical of an accretion disk, where the peaks are separated by ~320 ± 20 km/s. We measure a FWHM of ~550 ± 50 km/s for Hβ and Hα emission lines.
A dwarf nova classification is consistent with the evolution of the light-curve obtained by the All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014). The light-curve shows a quick rise to the maximum followed by a fast decline, typical for that of dwarf novae (see below a table of magnitudes) and consistent with our spectrum, taken 3.5-4 days after maximum.
Line identifications:
H I (Balmer): 4102, 4340, 4861 and 6563Å
He I: 5876, 6678, and 7065Å
H I (Paschen): 8545, 8598, 8665Å
HJD UT Date V mag err (mag)
2458229.90182 2018-04-21.3994796 >15.512 -----
2458230.86245 2018-04-22.3600368 12.424 0.019
2458230.86372 2018-04-22.3613106 12.412 0.018
2458231.84190 2018-04-23.3394140 12.822 0.031
2458231.84445 2018-04-23.3419512 12.775 0.032
2458233.74219 2018-04-25.2395443 13.210 0.023
2458233.74346 2018-04-25.2408134 13.183 0.021
2458233.77193 2018-04-25.2692827 13.289 0.036
2458233.91276 2018-04-25.4101013 13.263 0.021
2458233.91402 2018-04-25.4113609 13.311 0.021
2458233.91529 2018-04-25.4126282 13.297 0.022
2458234.90446 2018-04-26.4017210 13.593 0.082
2458236.71951 2018-04-28.2166377 13.806 0.083
2458236.76776 2018-04-28.2648782 13.768 0.042
2458236.76904 2018-04-28.2661528 13.811 0.044
2458236.77029 2018-04-28.2674156 13.883 0.048
2458238.89563 2018-04-30.3925952 14.008 0.053
2458238.89690 2018-04-30.3938607 14.142 0.069
2458240.89597 2018-05-02.3927761 14.284 0.103
2458241.82155 2018-05-03.3182910 14.555 0.074
2458241.82281 2018-05-03.3195491 14.459 0.058
ASAS-SN lightcurve