Cataclysmic Variables in the Second Year of the Zwicky Transient Facility

TL;DR

This study identifies and characterizes 372 cataclysmic variables using ZTF data, confirming several candidates spectroscopically and analyzing their distances and distribution, thus expanding the known CV population.

Contribution

It introduces a new selection method for CV candidates based on color and variability, and compares it with machine learning approaches to improve detection accuracy.

Findings

Identified 372 CV objects, including 93 confirmed and 279 candidates.

Spectroscopic analysis confirms CV nature and magnetic white dwarf features.

Distances range from 108 to 2096 parsecs, with most between 10.5 and 12.5 magnitude.

Abstract

Using a filter in the GROWTH Marshal based on color and the amplitude and the timescale of variability, we have identified 372 objects as known or candidate cataclysmic variables (CVs) during the second year of operation of the Zwicky Transient Facility (ZTF). From the available difference imaging data, we found that 93 are previously confirmed CVs, and 279 are strong candidates. Spectra of four of the candidates confirm them as CVs by the presence of Balmer emission lines, while one of the four has prominent HeII lines indicative of containing a magnetic white dwarf. Gaia EDR3 parallaxes are available for 154 of these systems, resulting in distances from 108-2096 pc and absolute magnitudes in the range of 7.5-15.0, with the largest number of candidates between 10.5-12.5. The total numbers are 21% higher than from the previous year of the survey with a greater number of distances available but a smaller percentage of systems close to the Galactic plane. Comparison of these findings with a machine learning method of searching all the light curves reveals large differences in each dataset related to the parameters involved in the search process.