The Inter-Eruption Timescale of Classical Novae from Expansion of the Z Camelopardalis Shell

TL;DR

This study uses the expansion of the Z Camelopardalis shell to estimate the inter-eruption timescale of classical novae, providing the first strong observational test of the >1000-year recurrence prediction.

Contribution

It presents the first observational constraint on the inter-eruption timescale of classical novae using shell expansion measurements, supporting the theory that these intervals exceed 1000 years.

Findings

Lower limit of 1300 years for the last eruption of Z Cam

No detectable shell expansion over 3 years, with an upper limit of 1 pixel/3 years

Ejecta velocity estimated at 85 km/s if associated with the 77 BCE nova

Abstract

The dwarf nova Z Camelopardalis is surrounded by the largest known classical nova shell. This 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. The current size of the shell, its known distance, and the largest observed nova ejection velocity set a lower limit to the time since Z Cam's last outburst of 220 years. The brightest part of the Z Cam shell's radius is currently p ~ 1690 pixels. No expansion of the radius of the brightest part of the ejecta was detected, with an upper limit of pdot < 1 pixel/3 years. This suggests that the last Z Cam eruption occurred p/pdot > 5,000 years ago. However, including the important effect of deceleration as the ejecta sweeps up interstellar matter in its snowplow phase reduces the lower limit to 1300 years. This is the first strong test of the prediction of nova thermonuclear runaway theory that the inter-outburst times of classical novae are longer than 1000 yr. The intriguing suggestion that Z Cam was a bright nova, recorded by Chinese imperial astrologers in October - November 77 BCE, is consistent with our measurements. If Z Cam was indeed the nova of 77 BCE we predict that its ejecta are currently expanding at 85 km/s, or 0.11 arcsec/yr. Detection and measurement of this rate of expansion are doable in just a few years.