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Paper: Optical spectroscopy of the supersoft X-ray source RX J0439.8--6809
Volume: 261, The Physics of Cataclysmic Variables and Related Objects
Page: 653
Authors: Reinsch, K.; Beuermann, K.; Gänsicke, B. T.
Abstract: Optical spectroscopy of the V~21 mag optical counterpart of the supersoft X-ray source RX J0439.8--6809 obtained with FORS1 at the ESO VLT revealed the existence of narrow, highly-excited emission lines of O vi and N v which are superimposed on an otherwise featureless blue continuum. No traces of H, He i, or He ii lines (seen in other supersoft X-ray sources) are detected. The average systemic velocity v0 = (250 +/- 30) kms of the O vi and N v lines corresponds to the LMC velocity and is so far the strongest evidence that RX J0439.8--6809 belongs to the LMC and is not a foreground star in the galactic halo. The line profiles are not resolved implying that the intrinsic Doppler velocity of the line emitting region must be small, i.e. | vd | <~ 190kms. The metal rich and helium poor spectrum is reminiscent of the extremely hot (~200,000 K) PG 1159 star H1504+65, except for the lack of C iv in RX J0439.8--6809.
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