IR STUDY OF NOVA V2468 Cyg FROM EARLY DECLINE TO THE CORONAL PHASE

Abstract

We present infrared spectroscopic and photometric observations of the nova V2468 Cyg covering the period from 2008 March 13 till 2008 November 11. The JHK spectra of the object have been taken from the Mount Abu Infrared Observatory using the Near-Infrared Imager/Spectrometer. Spectra from 0.8-5.2 µm are also presented that were obtained using the NASA Infrared Telescope Facility and the SPEX instrument. The spectra are dominated by strong H i lines from the Brackett and Paschen series, Fe ii, O i and C i lines in the initial days, typical of an Fe II type nova. The lines were broader in the period immediately after outburst with measured FWHM of 1800-2300 km s −1 for the Paβ and Brγ lines. These values narrowed to 1500-1600 km s −1 by 12 days from outburst. The spectra showed prominent He i lines at 1.0830 and 2.0581 µm together with H i and O i emission features after 36 days from outburst. Our IR observations show the comparatively broad emission lines, the rapid development of the spectrum to higher ionization, the early appearance of coronal lines, and the absence of dust emission, all features that indicate the hybrid nature of the nova. This is perhaps the most extensively observed example of a probable Fe IIb type nova at the infrared wavelengths. We also notice a short lived emission line of Fe II at 2.0888µm which was present between April 9, 2008 to May 9, 2008. No dust emission is seen from the nova ejecta. We have also estimated the range for the ejecta mass in V2468 Cyg to be 3 × 10 −6 -10 −5 M ⊙ .

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