The infrared coronal lines of recent novae

Abstract

We report the discovery of infrared coronal emission lines in Nova V1819 Cyg and Nova V827 Her and present new high-resolution near-infrared spectra of coronal line emission in Nova QU Vul. These new results increase the number of known infrared coronal line novae from two to four and show that each of the four is characterized by approximately the same [Si VI]/[Si VII] line intensity ratio that reflects a common coronal zone electron temperature of approximately 3 × 105 K among these novae. Among the most interesting results of our study of novae is that each coronal line nova exhibits a remarkably similar near-infrared spectrum. This uniformity suggests that coronal line emission in novae will be only occasionally observed at optical wavelengths. The abundance pattern for Al and Mg, is derived for two of the coronal line novae discussed, and the Ne abundance pattern is derived for QU Vul. We find that these novae are substantially overabundant in these elements. These data double the number of novae for which Al and Mg abundances have been determined. Observational evidence for novae outbursts on oxygen-neon-magnesium white dwarfs is increased as a consequence. The first speckle interferometry of the coronal line emission region of a nova is presented. The coronal zone of QU Vul was spatially resolved at 0″.6 using this technique in the 3.02 μm [Mg VIII] line. Comparison of our interferometry to high-resolution VLA maps of QU Vul suggests that the coronal line emission region encompasses the principal ejecta of the nova. We present a new technique for interpreting the coronal line spectra that relates their infrared spectral evolution to electron temperature and density gradients in the expanding ejecta. The relative role of collisional ionization and photoionization in formation of the coronal species is discussed in detail. We find that photoionization alone cannot account for the observed ionization. Observational tests which will improve current understanding of the spectral evolution of novae and model constraints which result from these data are suggested.