An Adaptive Optics Census of Companions to Northern Stars Within 25 pc
  with Robo-AO
  In order to assess the multiplicity statistics of stars across spectral types
and populations in a volume-limited sample, we censused nearby stars for
companions with Robo-AO. We report on observations of 1157 stars of all
spectral types within 25 pc with decl. $>-13^{\circ}$ searching for tight
companions. We detected 154 companion candidates with separations ranging from
$\sim$0.15$''$ to 4.0$''$ and magnitude differences up to
$\Delta$m$_{\textit{i'}}\le$7 using the robotic adaptive optics instrument
Robo-AO. We confirmed physical association from Gaia EDR3 astrometry for 53 of
the companion candidates, 99 remain to be confirmed, and 2 were ruled out as
background objects. We complemented the high-resolution imaging companion
search with a search for co-moving objects with separations out to 10,000 AU in
Gaia EDR3, which resulted in an additional 147 companions registered. Of the
301 total companions reported in this study, 49 of them are new discoveries.
Out of the 191 stars with significant acceleration measurements in the
Hipparcos-Gaia catalog of accelerations, we detect companions around 115 of
them, with the significance of the acceleration increasing as the companion
separation decreases. From this survey, we report the following multiplicity
fractions (compared to literature values): 40.9%$\pm$3.0% (44%) for FGK stars
and 28.2%$\pm$2.3% (27%) for M stars, as well as higher-order fractions of
5.5%$\pm$1.1% (11%) and 3.9%$\pm$0.9% (5%) for FGK stars and M type stars,
respectively.
