Rise and fall of the dust shell of the classical nova V339 Delphini

Abstract

We present infrared spectroscopy of the classical nova V339 Del, obtained over a ∼ 2 year period. The in- frared emission lines were initially symmetrical, with HWHM velocities of 525 km s−1. In later (t >∼ 77days, where t is the time from outburst) spectra however, the lines displayed a distinct asymmetry, with a much stronger blue wing, possibly due to obscuration of the receding component by dust. Dust formation com- menced at ∼ day 34.75 at a condensation temperature of 1480 ± 20 K, consistent with graphitic carbon. Thereafter the dust temperature declined with time as Td ∝ t−0.346, also consistent with graphitic carbon. The mass of dust initally rose, as a result of an increase in grain size and/or number, peaked at ∼ day 100, and then declined precipitously. This decline was most likely caused by grain shattering due to electrostatic stress after the dust was exposed to X-radiation. An Appendix summarises Planck Means for carbon, and the determination of grain mass and radius for a carbon dust shell.