An X-ray emission line spectrum of Nova V382 Velorum 1999

Abstract

We report on the analysis of an X-ray grating spectrum of the Classical Nova V382 Vel (1999), obtained with the LETG+HRC-S instrument on board CHANDRA, which shows emission lines dominating over any continuum. Lines of Si, Mg, Ne, O, N, and C are identified, but no Fe lines are detected. The total luminosity in the lines is 4x10^27erg/s (corrected for N_H=1.2x10^21cm^-2). The lines have broad profiles with FWHM corresponding to a velocity 2900+-200km/s. Some structure is identified in the profiles, but for different elements we find different profile structures. While lines of O show a broadened Gaussian profile, those of Ne are double-peaked, suggesting a fragmented emitting plasma. Using the emission measure distribution we derive relative element abundances and find abundances of Ne and N that are significantly enhanced relative to that of O, while Fe is not over-abundant. The lack of any source emission longwards of 50A and the OVIII Ly_alpha/Ly_beta line ratio support previous values of the hydrogen column-density. We find weak continuum emission from the white dwarf, consistent with a black-body spectrum with an upper limit to the temperature of T=3x10^5K, assuming a source radius of 6000km. The upper limit for the integrated black-body luminosity is 2x10^36erg/s. The BeppoSAX and Chandra ACIS observations of V382 Vel show that the nova was bright and in the Super Soft phase as late as 1999 December 30. Our LETG observation obtained 6 weeks later, as well as all subsequent X-ray observations, showed a remarkable fading to a nearly pure emission line phase which suggests that nuclear burning on the white dwarf had turned off by February. In the absence of a photoionizing source the emission lines were formed in a collisionally ionized and excited expanding shell.