摘要：Aims.We aim to confirm whether the eclipsing cataclysmic variable (CV) V902 Mon is an intermediate polar (IP), to characterise its X-ray spectrum and flux, and to refine its orbital ephemeris and spin period.Methods.We performed spectrographic observations of V902 Mon in 2016 with the 2.2 m Calar Alto telescope, and X-ray photometry and spectroscopy withXMM-Newtonin October 2017. This data was supplemented by several years of AAVSO visual photometry.Results.We confirmed V902 Mon as an IP based on detecting the spin period, which has a value of 2208 s, at multiple epochs. Spectroscopy of the donor star andGaiaparallax yield a distance of 3.5−0.9+1.3kpc, suggesting an X-ray luminosity one or two orders of magnitude lower than the 1033erg s−1typical of previously known IPs. The X-ray to optical flux ratio is also very low. The inclination of the system is more than 79°, and is most likely a value of around 82°. We have refined the eclipse ephemeris, stable over 14 000 cycles. The Hαline is present throughout the orbital cycle and is clearly present during eclipse, suggesting an origin distant from the white dwarf, and shows radial velocity variations at the orbital period. The amplitude and overall recessional velocity seem inconsistent with an origin in the disc. TheXMM-Newtonobservation reveals a partially absorbed plasma model typical of magnetic CVs, that has a fluorescent iron line at 6.4 keV showing a large equivalent width of 1.4 keV.Conclusions.V902 Mon is an IP, and probably a member of the hypothesized X-ray underluminous class of IPs. It is likely to be a disc accretor, although the radial velocity behaviour of the Hαline remains puzzling. The large equivalent width of the fluorescent iron line, the smallFX/Foptratio, and the only marginal detection of X-ray eclipses suggests that the X-ray emission arises from scattering.
