IM Normae: The Death Spiral of a Cataclysmic Variable?

TL;DR

This study analyzes the orbital light curves of the recurrent nova IM Normae, revealing a rapidly increasing orbital period and high accretion rates, suggesting it is in a final evolutionary stage driven by irradiation-induced mass transfer.

Contribution

It provides the first detailed orbital period change analysis of IM Normae, linking high accretion rates to its evolutionary state and comparing it to T Pyxidis.

Findings

Orbital period increasing on a timescale of 1.28 million years.

High accretion rate near 10^-7 solar masses per year.

IM Normae resembles T Pyxidis in behavior and evolution.

Abstract

We present a study of the orbital light curves of the recurrent nova IM Normae since its 2002 outburst. The broad "eclipses" recur with a 2.46 hour period, which increases on a timescale of 1.28(16)x10^6 years. Under the assumption of conservative mass-transfer, this suggests a rate near 10^-7 M_sol/year, and this agrees with the estimated /accretion/ rate of the postnova, based on our estimate of luminosity. IM Nor appears to be a close match to the famous recurrent nova T Pyxidis. Both stars appear to have very high accretion rates, sufficient to drive the recurrent-nova events. Both have quiescent light curves which suggest strong heating of the low-mass secondary, and very wide orbital minima which suggest obscuration of a large "corona" around the primary. And both have very rapid orbital period increases, as expected from a short-period binary with high mass transfer from the low-mass component. These two stars may represent a final stage of nova -- and cataclysmic-variable -- evolution, in which irradiation-driven winds drive a high rate of mass transfer, thereby evaporating the donor star in a paroxysm of nova outbursts.