Discovery of Faint Nebulosity Around a Z Camelopardalis-type Cataclysmic Variable in Antlia: Nova Shell or Ancient Planetary Nebula?

TL;DR

This paper reports the discovery of a faint bipolar nebula around the CV star ASASSN-19ds, exploring its possible origins as either nova ejecta or an ancient planetary nebula, and characterizing its properties.

Contribution

It provides the first detailed imaging and analysis of the nebula around a Z Camelopardalis-type CV, and discusses potential origins of the nebula with new observational data.

Findings

Discovered a bipolar nebula around ASASSN-19ds

Confirmed ASASSN-19ds as a Z Camelopardalis-type CV

Identified the nebula's possible origins as nova ejecta or planetary nebula

Abstract

We report our discovery of a faint nebula surrounding a previously little-studied 15th-mag variable star, ASASSN-19ds, in the southern-hemisphere constellation Antlia. Spectra verify that the star is a cataclysmic variable (CV). Using new and archival photometry, we confirm that ASASSN-19ds is an eclipsing binary with an orbital period of 0.139 days (3.34 hr). Moreover, its out-of-eclipse brightness shows a "sawtooth" light curve with an amplitude of $\sim$1~mag and an interval between peaks that varies between about three to nearly five weeks. Its mean absolute magnitude in the Gaia system is $M_G=+6.5$. These combined properties lead to a classification of ASASSN-19ds as a Z Camelopardalis-type CV. We obtained deep narrow-band images of the nebulosity, using modest-sized telescopes and extremely long exposure times. Our imagery reveals a bipolar morphology, with thin arcs at the ends of the major axis, likely indicating an interaction with the interstellar medium. We consider several scenarios for the origin of the nebula, but from the existing information we are unable to distinguish between it being ejecta from an unobserved classical-nova outburst several centuries ago, or an ancient planetary nebula. Future observations should be able to decide between these possibilities. At the star's distance of only $\sim$557 pc, a nova eruption would have been a spectacular naked-eye event.