XMM-Newton RGS observations of the cat's eye nebula

We present an analysis of XMM-Newton Reflection Grating Spectrometer (RGS) observations of the planetary nebula (PN) NGC6543. These observations render it the second PN with high-resolution X-ray spectroscopic observations after BD +30°3639. The observations consist of 26 pointings, 14 of which included RGS observations for a total integration time of 435 ks.Many of these observations, however, were severely affected by high-background levels, and the net useful exposure time is drastically reduced to 25 ks. Only the O VII triplet at 22 A˚ is unambiguously detected in the RGS spectrum of NGC6543. We find this spectrum consistent with an optically thin plasma at 0.147 keV (1.7 MK) and nebular abundances. Unlike BD +30°3639, the X-ray emission from NGC6543 does not reveal overabundances of C and Ne. The results suggest that the N/O ratio of the hot plasma is consistent with that of the stellar wind, that is, it is lower than the nebular N/O ratio, but this result is not conclusive.