Elemental abundances in NGC 3516

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 ≲, 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 ≲ 0.01 keV). The availability of emission lines from different elements for two isoelectronic 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.