Ongoing near-infrared observations of V339 Del (Nova Del 2013)

ATel #5404; D. P. K. Banerjee , N. M. Ashok & Vishal Joshi (1) and Nye Evans (2); (1) - Physical Research Laboratory, Ahmedabad, India ; (2) Astrophysics Group, Keele University, U. K.
on 20 Sep 2013; 17:22 UT
Credential Certification: Dipankar P.K. Banerjee (orion@prl.res.in)

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We report continuing 1.08 to 2.35 micron near-infrared spectroscopy of Nova Del 2013 in the J,H,K bands with the Mount Abu 1.2 meter telescope (+ PRL Near-Infrared NICMOS3 Imager/Spectrograph). Subsequent to our initial report on August 28.674 UT (ATel #5337), spectra of the nova have been obtained at regular intervals. The latest spectra of September 16.5 and 19.5 UT are dominated by strong emission lines but the earlier reported strengths of many of the lines have changed significantly. In the Sept 19.5 spectra, the most striking development is the fairly rapid increase in the intensity of the He I lines at 2.0581 and 1.0830 micron, a clear indication that the radiation field is hardening. Hydrogen lines still remain strong viz H I Paschen-beta and Paschen-gamma, Brackett-gamma and Brackett 10 to 20 in the H band. However the O I line at 1.1287 micron is by far the strongest line indicating a considerable contribution from Lyman beta fluorescence. This line has an EW of -378 nm compared to an EW of -135 nm of the strongest HI line seen viz. Paschen beta. The ratio of OI 1.1287 to OI 1.3164 is approximately 75. The carbon lines reported earlier (ATel #5336, #5337) are still present but have weakened considerably in a manner consistent with their expected temporal evolution in the Fe II class of novae (Banerjee & Ashok; BASI, 2012, 40, 243). For e.g. the intensity of of the CI 1.175 micron line was almost equal to that of Pa beta on 28/29 August; at present it is ~ 0.17 times the Pa beta line strength.

No molecular first overtone CO emission has been seen in the K band during the entire duration of our observations. The unidentified 2.0890 micron feature in the K band has also been present for some time. At the moderate R = 1000 resolution of the spectra, hints of a triple peaked structure (central peak strongest) are being consistently seen in the HI line profiles, especially for Br gamma at 2.1656 micron, possibly suggesting a bipolarity in the flow. The nova has remained bright in the near-IR; we measure J = 5.64, H = 5.71, K = 5.54 on September 10.6 UT (also see ATels #5294, #5317 and #5340 for earlier IR photometric results).