When does an old nova become a dwarf nova? Kinematics and age of the nova shell of the dwarf nova AT Cnc

TL;DR

This study measures the age of the nova shell around AT Cnc, revealing it last erupted approximately 330 years ago, supporting the hibernation model of cataclysmic binaries and linking it to historical observations.

Contribution

It provides the first precise age estimate of AT Cnc's nova shell using radial velocity measurements, confirming rapid transition predicted by the hibernation scenario.

Findings

AT Cnc's last nova eruption occurred about 330 years ago.

The nova shell's age aligns with historical observations from 1645 CE.

Supports the hibernation model of cataclysmic binary evolution.

Abstract

The Z Cam-type dwarf nova AT Cnc displays a classical nova (CN) shell, demonstrating that mass transfer in cataclysmic binaries decreases substantially after a CN eruption. The hibernation scenario of cataclysmic binaries predicts such a decrease, on a timescale of a few centuries. In order to measure the time since AT Cnc's last CN eruption, we have measured the radial velocities of a hundred clumps in its ejecta with SITELLE, CFHT's recently commissioned imaging Fourier transform spectrometer. These range from -455 to +490 km/s. Coupled with the known distance to AT Cnc of 460 pc (Shara 2012), the size of AT Cnc's shell, and a simple model of nova ejecta deceleration, we determine that the last CN eruption of this system occurred $330_{-90}^{+135}$ years ago. This is the most rapid transition from a high mass transfer rate, novalike variable to a low mass transfer rate, dwarf nova yet measured, and in accord with the hibernation scenario of cataclysmic binaries. We conclude by noting the similarity in deduced outburst date (within a century of 1686 CE) of AT Cnc with a "guest star" reported in the constellation Cancer by Korean observers in 1645 CE.