Infrared observations show that Nova Mon 2012 is now in the coronal line phase

ATel #4542; D. P.K. Banerjee, N. M. Ashok and V. Venkataraman (Astronomy and Astrophysics Division, Physical Research Laboratory, Ahmedabad, India)
on 5 Nov 2012; 09:33 UT
Credential Certification: Dipankar P.K. Banerjee (orion@prl.res.in)

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Near infrared spectra in the 1.08 to 2.25 micron region show that Nova Mon 2012 has entered the coronal line phase. The spectra were obtained on 1 and 2 November 2012 at R ~ 1000 using the NICMOS-3 Imager/Spectrograph and the 1.2m Mount Abu Observatory telescope of the Physical Research Laboratory, India. Nova Mon 2012, whose gamma ray detection on 2012 June 22 (ATel # 4224) uncharacteristically preceded its optical discovery on 2012 9 August (CBET # 3202), is one among the small & special group of 3 known novae that have a gamma-ray transient associated with the erupting optical counterpart. From its AAVSO light curve it is seen that the object is evolving rather slowly for a He/N class of nova having declined by just 1.2 magnitudes in V since its optical discovery. The object is being actively pursued at several wavelengths (ATel # 4310, 4320, 4321, 4352, 4365, 4376, 4408).

Among the coronal lines, we detect [Si VI] 1.9641 strongly. Although the large line widths cause [Si VI] 1.9641 to blend with Brackett 8 at 1.9446 micron on the blue wing, the presence of the forbidden Si line is unambiguous. A line seen at 1.2530 micron should be due to [S IX] 1.2520 combined with He I 1.2534. The [Ti VI] 1.7155 micron line is also possibly being detected and we also suspect the presence of [Al IX] 2.040 on the blue wing of the He I 2.0581 micron line. The overall spectra are dominated by strong emission from He I and Brackett (Br) and Paschen (Pa)lines of hydrogen. The He I lines detected are those at 1.0831, 1.7002, 2.1120 + 2.1132 and 2.0581 micron. He II lines at 1.1636 and 2.1882 micron are also seen. On the whole, He I 1.0831 is overwhelmingly the strongest line in the spectrum. The H lines seen are Pa alpha, Pa beta; Br gamma, Br 8 & Br 10 to 17 in the H band. The Br 10 line at 1.7362 micron appears stronger than expected which could be due to a contribution from [P VIII] expected at the same wavelength. The 1.1287 and 1.3164 micron lines of O I are also detected as also three unidentified lines at 1.1101, 1.1908 and 2.09 micron - the last line could be due to [Mn XIV] 2.092. Further spectroscopic monitoring of the object is most desirable to track its spectral evolution.

Most of the H and HeI lines show a double peaked structure at our spectral resolution. The FWHM of most of the lines is of the order of 2200 +- 200 km/s which is similar to the FWHMs observed on 20 August 2012 (ATel # 4320) indicating no significant deceleration of the ejecta over the intervening period.