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Near-infrared spectroscopy confirms ASASSN-17nj as a Galactic Nova

ATel #10852; Vishal Joshi, Dipankar P. K. Banerjee and Mudit Srivastava (Physical Research Laboratory, Ahmedabad, India)
on 15 Oct 2017; 18:02 UT
Credential Certification: Vishal Joshi (vjoshi@prl.res.in)

Subjects: Infra-Red, Nova, Transient

Referred to by ATel #: 10857, 10862

We report a near-IR spectrum in the 0.85 to 1.35 micron region of ASASSN-17nj reported in ATel #10850 to be a possible nova candidate. Observations were made on UT 2017-10-15.58 using the Near IR spectrograph (NICS) deployed on the 1.2m Mount Abu observatory telescope when the object was close to setting and at high airmass. The spectrum is hence noisy but allows us to identify the object as a possible classical nova of the He/Ne class. There are however some peculiarities. Paschen beta (1.2818 micron), Paschen gamma (1.094 micron) and HeI (1.083 micron) are all present with strong P-Cygni profiles. OI 1.1287 is also seen. The peak-to-trough velocities for the first two mentioned hydrogen lines are 1600 and 1850 km/s respectively. NI 1.2461, 1.2469 micron is clearly seen supporting the He/N classification but at the same time weak emission is also seen in some of the carbon lines (e.g CI 1.069, 1.175 microns respectively) which are expected very prominently in a Fe II class nova. Further, in contrast to what is generally expected for a He/N nova the lines are sharp peaked instead of flat or castellated, the P-Cygni absorption features are strong and the velocities are marginally on the lower side than expected for the class. There is considerable reddening of the spectrum implying high extinction. This is supported by our JHKs magnitudes of 6.7, 5.9 and 5.4 respectively showing the object is very bright in the NIR whereas it was reported to be fairly faint optically in the discovery report at V ~14.0 on UT 2017-10-14.01 (ATel #10850). Monitoring of this interesting object is worthwhile.