Collisional Heating of Dust in the 1985 Outburst of RS Ophiuchi

Extended Summary

The recurrent nova RS Ophiuchi has undergone a number of outbursts this century. Investigation of the interoutburst state (Feast & Glass 1974) has shown that it is heavily reddened and has a substantial circumstellar dust shell. That this shell is dusty is suggested by a detection of RS Oph at 12 μm by the IRAS in 1983, the flux density being well in excess of an extrapolation from near infrared (JHKL) wavelengths. There is no doubt that the circumstellar shell is an accumulation of material ejected in previous outbursts and in a wind from the (evolved) secondary component. At outburst we can expect a strong interaction between the radiation pulse from the nova, the ejecta and the circumstellar shell. The most recent outburst occurred in 1985 January (Morrison 1985). The outburst was discovered before visual maximum, which occured on JD2446095.5 (Jan 29.5); visual maximum is taken as the origin of time hereafter. We describe here a possible interpretation of the JHKL infrared photometry obtained on the 0.75m and 1.9m telescopes at the South African Astronomical Observatory (SAAO) since day 5, and made available by Dr. P.A. Whitelock and colleagues.