XMM-Newton RGS observations of the Cat’s Eye Nebula

摘要

We present an analysis of XMM-Newton Reflection Grating Spectrometer (RGS) observations of the planetary nebula (PN) NGC?6543. 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 ? is unambiguously detected in the RGS spectrum of NGC?6543. 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 NGC?6543 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.