# A spectroscopic search for White Dwarf companions to 101 nearby M dwarfs

## TL;DR

This study used intermediate resolution spectroscopy to search for hidden white dwarf companions around 101 nearby M dwarfs, finding no clear evidence but setting upper temperature limits and constraining their frequency.

## Contribution

It provides the first systematic spectroscopic search for white dwarf companions to nearby M dwarfs and establishes upper limits on their occurrence for WDs hotter than 5300 K.

## Key findings

- No white dwarf companions detected in the spectra.
- The survey is sensitive to WDs hotter than approximately 5300 K.
- The frequency of undetected WD companions with T<5300 K is less than 3% at 95% confidence.

## Abstract

Recent studies of the stellar population in the solar neighborhood (<20 pc) suggest that there are undetected white dwarfs (WDs) in multiple systems with main sequence companions. Detecting these hidden stars and obtaining a more complete census of nearby WDs is important for our understanding of binary and galactic evolution, as well as the study of explosive phenomena. In an attempt to uncover these hidden WDs, we present intermediate resolution spectroscopy over the wavelength range 3000-25000 \AA\ of 101 nearby M dwarfs (dMs), observed with the Very Large Telescope X-Shooter spectrograph. For each star we search for a hot component superimposed on the dM spectrum. X-Shooter has excellent blue sensitivity and thus can reveal a faint hot WD despite the brightness of its red companion. Visual examination shows no clear evidence of a WD in any of the spectra. We place upper limits on the effective temperatures of WDs that may still be hiding by fitting dM templates to the spectra, and modeling WD spectra. On average our survey is sensitive to WDs hotter than about 5300 K. This suggests that the frequency of WD companions of T<5300 K with separation of order <50 AU among the local dM population is <3% at the 95% confidence level. The reduced spectra are made available on via WISeREP repository.