  Pulsed X-ray emission in the luminous, helium-rich sdO BD+37 442 has recently
been discovered (La Palombara et al., 2012). It was suggested that the sdO star
has a neutron star or white dwarf companion with a spin period of 19.2 s. After
HD 49798, which has a massive white dwarf companion spinning at 13.2 s in an
1.55 day orbit, this is only the second O-type subdwarf from which X-ray
emission has been detected. We report preliminary results of our ongoing
campaign to obtain time-resolved high-resolution spectroscopy using the CAFE
instrument at Calar Alto observatory and SARG at the Telescopio Nationale
Galileo. Atmospheric parameters were derived via a quantitative NLTE spectral
analysis. The line fits hint at an unusually large projected rotation velocity.
Therefore it seemed likely that BD+37 442 is a binary similar to HD 49798 and
that the orbital period is also similar. The level of X-ray emission from BD+37
442 could be explained by accretion from the sdO wind by a neutron star
orbiting at a period of less than ten days. Hence, we embarked on radial
velocity monitoring in order to derive the binary parameters of the BD+37 442
system and obtained 41 spectra spread out over several month in 2012. Unlike
for HD\,49798, no radial velocity variations were found and, hence, there is no
dynamical evidence for the existence of a compact companion yet. The origin of
the pulsed X-ray emission remains as a mystery.
