We present Reflection Grating Spectrometer data from an XMM-Newton observation of the Seyfert 1 galaxy NGC 3516 , taken while the continuum source was in an extremely low flux state .
This observation offers a rare opportunity for a detailed study of emission from a Seyfert 1 galaxy as these are usually dominated by high nuclear continuum levels and heavy absorption .
The spectrum shows numerous narrow emission lines ( FWHM \lesssim 1300 km s ^ { -1 } ) in the 0.3 – 2 keV range , including the H-like lines of C , N , and O and the He-like lines of N , O and Ne .
The emission-line ratios and the narrow width of the radiative recombination continuum of C vi indicate that the gas is photoionized and of fairly low temperature ( kT \lesssim 0.01 keV ) .
The availability of emission lines from different elements for two iso-electronic sequences allows us to constrain the element abundances .
These data show that the N lines are far stronger than would be expected from gas of solar abundances .
Based on our photoionization models we find that nitrogen is overabundant in the central regions of the galaxy , compared to carbon , oxygen and neon by at least a factor of 2.5 .
We suggest that this is the result of secondary production of nitrogen in intermediate mass stars , and indicative of the history of star formation in NGC 3516 .