Stelzer, B.B.StelzerDE MARTINO, DomitillaDomitillaDE MARTINOCasewell, S. L.S. L.CasewellWynn, G. A.G. A.WynnRoy, M.M.Roy2020-09-102020-09-1020170004-6361http://hdl.handle.net/20.500.12386/27279In an XMM-Newton observation of the binary SDSS J121209.31+013627.7, consisting of a white dwarf and an L dwarf, we detect X-ray orbital modulation as proof of accretion from the substellar companion onto the magnetic white dwarf. We constrain the system geometry (inclination as well as magnetic and pole-cap angle) through modelling of the X-ray light curve, and we derive a mass accretion rate of 3.2 × 10<SUP>-14</SUP>M<SUB>☉</SUB>/ yr from the X-ray luminosity ( 3 × 10<SUP>29</SUP> erg/s). From X-ray studies of L dwarfs, a possible wind driven from a hypothesized corona on the substellar donor is orders of magnitude too weak to explain the observed accretion rate, while the radius of the L dwarf is comparable to its Roche lobe (0.1 R<SUB>☉</SUB>), making Roche-lobe overflow the likely accretion mechanism in this system.STAMPAenArticle10.1051/0004-6361/2016300382-s2.0-85010986791000394465000143https://www.aanda.org/articles/aa/abs/2017/02/aa30038-16/aa30038-16.html2017A&A...598L...6SFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering