Rise and fall of silicate dust in RS Ophiuchi following the 2006 eruption

Abstract

We present an analysis of archival Spitzer InfraRed Spectrograph (IRS) observations of the recurrent nova RS Ophiuchi obtained on several occasions, beginning about 7 months after the outburst in 2006. These data show atomic emission lines, absorption bands due to photospheric SiO, and the well known silicate dust features at 9.7 µm and 18 µm. The dust emission, arising in the wind of the secondary star, is ?tted by Dusty models for mass-loss rates in the range 1.0 - 1.7 × 10-7 M?yr-1. The silicate features are similar in pro?le to those seen in circumstellar environments of isolated late-type stars and some dusty symbiotic binaries, although the longer wavelength feature peaks at 17 µm, instead of the usual 18 µm, indicating peculiar grain properties. The dust features are variable, appearing stronger in 2006-2007 during outburst than in 2008-2009 when the system was in the quiescent state. This variability is attributed to changes in the ultraviolet output and the reformation of the accretion disk, although a decline in the mass-loss rate of the red giant secondary star could also play a role. Further observations, in the aftermath of the 2021 eruption, could provide a de?nitive conclusion