We report on X-ray spectroscopic observations with XMM/Newton of the ultracompact , double white dwarf binary , GP Com .
With the Reflection Grating Spectrometers ( RGS ) we detect the L \alpha and L \beta lines of hydrogen-like nitrogen ( N VII ) and neon ( Ne X ) , as well as the helium-like triplets ( N VI and Ne IX ) of these same elements .
All the emission lines are unresolved .
These are the first detections of X-ray emission lines from a double-degenerate , AM CVn system .
We detect the resonance ( r ) and intercombination ( i ) lines of the N VI triplet , but not the forbidden ( f ) line .
The implied line ratios for N VI , R = f / i < 0.3 , and G = ( f + i ) / r \approx 1 , combined with the strong resonance line are consistent with formation in a dense , collision-dominated plasma .
Both the RGS and EPIC/MOS spectra are well fit by emission from an optically thin thermal plasma with an emission measure ( EM ) \propto ( kT / 6.5 { keV } ) ^ { 0.8 } 
( model cevmkl in XSPEC ) .
Helium , nitrogen , oxygen and neon are required to adequately model the spectrum , however , the inclusion of sulphur and iron further improves the fit , suggesting these elements may also be present at low abundance .
We confirm in the X-rays the underabundance of both carbon and oxygen relative to nitrogen , first deduced from optical spectroscopy by Marsh et al .
The average X-ray luminosity of \approx 3 \times 10 ^ { 30 } ergs s ^ { -1 } implies a mass accretion rate \dot { m } \approx 9 \times 10 ^ { -13 } M _ { \odot } { yr } ^ { -1 } .
The implied temperature and density of the emitting plasma , combined with the presence of narrow emission lines and the low \dot { m } value , are consistent with production of the X-ray emission in an optically thin boundary layer just above the surface of the white dwarf .