Title: A Spectroscopic Orbit for the late-type Be star $β$ CMi,
Abstract: The late-type Be star $\beta$ CMi is remarkably stable compared to other Be
stars that have been studied. This has led to a realistic model of the
outflowing Be disk by Klement et al. These results showed that the disk is
likely truncated at a finite radius from the star, which Klement et al.~suggest
is evidence for an unseen binary companion in orbit. Here we report on an
analysis of the Ritter Observatory spectroscopic archive of $\beta$ CMi to
search for evidence of the elusive companion. We detect periodic Doppler shifts
in the wings of the H$\alpha$ line with a period of 170 d and an amplitude of
2.25 km s$^{-1}$, consistent with a low-mass binary companion ($M\approx 0.42
M_\odot$). We then compared the small changes in the violet-to-red peak height
changes ($V/R$) with the orbital motion. We find weak evidence that it does
follow the orbital motion, as suggested by recent Be binary models by Panoglou
et al. Our results, which are similar to those for several other Be stars,
suggest that $\beta$ CMi may be a product of binary evolution where Roche lobe
overflow has spun up the current Be star, likely leaving a hot subdwarf or
white dwarf in orbit around the star. Unfortunately, no direct sign of this
companion star is found in the very limited archive of {\it International
Ultraviolet Explorer} spectra.