AT Cnc: A Second Dwarf Nova with a Classical Nova Shell

TL;DR

This paper reports the discovery of a nova shell around the dwarf nova AT Cnc, supporting the idea that some dwarf novae have undergone classical nova eruptions, and suggests a link between classical novae and dwarf novae.

Contribution

It presents the second known nova shell around a Z Cam-type dwarf nova, providing evidence for the hibernation scenario and expanding understanding of nova evolution.

Findings

Detection of a 3 arcmin shell around AT Cnc

Shell morphology suggests bipolar ejection

Spectral similarity to classical nova ejecta

Abstract

We are systematically surveying all known and suspected Z Cam-type dwarf novae for classical nova shells. This survey is motivated by the discovery of the largest known classical nova shell, which surrounds the archetypal dwarf nova Z Camelopardalis. The Z Cam shell demonstrates that at least some dwarf novae must have undergone classical nova eruptions in the past, and that at least some classical novae become dwarf novae long after their nova thermonuclear outbursts, in accord with the hibernation scenario of cataclysmic binaries. Here we report the detection of a fragmented "shell", 3 arcmin in diameter, surrounding the dwarf nova AT Cancri. This second discovery demonstrates that nova shells surrounding Z Cam-type dwarf novae cannot be very rare. The shell geometry is suggestive of bipolar, conical ejection seen nearly pole-on. A spectrum of the brightest AT Cnc shell knot is similar to that of the ejecta of the classical nova GK Per, and of Z Cam, dominated by [NII] emission. Galex FUV imagery reveals a similar-sized, FUV-emitting shell. We determine a distance of 460 pc to AT Cnc, and an upper limit to its ejecta mass of ~ 5 x 10^{-5} Msun, typical of classical novae.