Ultra-short Period Binaries from the Catalina Surveys

TL;DR

This study identifies and confirms new ultra-short period binary systems, including rare M-dwarf+M-dwarf and white dwarf+M-dwarf binaries, significantly expanding the known sample through photometric and spectroscopic analysis.

Contribution

It provides the first spectroscopic confirmation of M-dwarf contact binaries and discovers rare white dwarf+M-dwarf systems, increasing the known ultra-short period binaries by over tenfold.

Findings

Confirmed M-dwarf+M-dwarf contact binaries.

Discovered rare white dwarf+M-dwarf binaries.

Expanded the catalog of ultra-short period binaries by more than ten times.

Abstract

We investigate the properties of 367 ultra-short period binary candidates selected from 31,000 sources recently identified from Catalina Surveys data. Based on light curve morphology, along with WISE, SDSS and GALEX multi-colour photometry, we identify two distinct groups of binaries with periods below the 0.22 day contact binary minimum. In contrast to most recent work, we spectroscopically confirm the existence of M-dwarf+M-dwarf contact binary systems. By measuring the radial velocity variations for five of the shortest-period systems, we find examples of rare cool-white dwarf+M-dwarf binaries. Only a few such systems are currently known. Unlike warmer white dwarf systems, their UV flux and their optical colours and spectra are dominated by the M-dwarf companion. We contrast our discoveries with previous photometrically-selected ultra-short period contact binary candidates, and highlight the ongoing need for confirmation using spectra and associated radial velocity measurements. Overall, our analysis increases the number of ultra-short period contact binary candidates by more than an order of magnitude.