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 Å 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 _ { \textrm { eff } } \gtrsim 5300 \textrm { K } with separation of order \lesssim 50 AU among the local dM population is < 3 % at the 95 % confidence level .
The reduced spectra are made available on via WISeREP http : //wiserep.weizmann.ac.il repository .