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We report the results of a new \textit{XMM-Newton} observation of thehelium-rich hot subdwarf BD+37$^{\circ}$442 carried out in February 2016. Thepossible periodicity at 19 s seen in a 2011 shorter observation is notconfirmed, thus dismissing the evidence for a binary nature. This implies thatthe observed soft X-ray emission, with a luminosity of a few 10$^{31}$ergs$^{-1}$, originates in BD+37$^{\circ}$442 itself, rather than in anaccreting neutron star companion. The X-ray spectrum is well fit by thermalplasma emission with a temperature of 0.22 keV and non-solar elementabundances. Besides the overabundance of He, C and N already known fromoptical/UV studies, the X-ray spectra indicate also a significant excess of Ne.The soft X-ray spectrum and the ratio of X-ray to bolometric luminosity,L$_{\rm X}$/L$_{\rm BOL}\sim2\times10^{-7}$, are similar to those observed inmassive early-type stars. This indicates that the mechanisms responsible forplasma shock-heating can work also in the weak stellar winds (mass loss rates$\dot M_{\rm W} \leq10^{-8}$ ${\rm M}_{\odot}$ yr$^{-1}$) of low-mass hotstars.

The lack of X-ray pulsations in the extreme helium star BD+37$^{\circ}$442 and its possible stellar wind X-ray emission