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Cat's Eye Nebula
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Title: XMM-Newton RGS observations of the Cat's Eye Nebula
Author: M.A. Guerrero, J.A. Toalį, Y.-H. Chu, R.A. Gruendl

We present an analysis of XMM-Newton Reflection Grating Spectrometer (RGS) observations of the planetary nebula (PN) NGC 6543, rendering it the second PN with high resolution X-ray spectroscopic observations besides BD+30 3639. The observations consist of 26 pointings, of which 14 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 \AA\ 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 the case of BD+30 3639, the X-ray emission from NGC 6543 does not reveal overabundances of C and Ne. The results suggest the N/O ratio of the hot plasma is consistent with that of the stellar wind, i.e., lower than the nebular N/O ratio, but this result is not conclusive.

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RE: NGC 6543
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On August 29, 1864, Sir William Huggins was the first to take the spectrum of a planetary nebula when he analysed NGC 6543
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The Cat's Eye Nebula or NGC 6543 was discovered by William Herschel on February 15, 1786
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Title: Looking deep into the Cat's Eye: Structure and rotation in the fast wind of the PN central star of NGC6543
Authors: R.K. Prinja, D.L. Massa, M. Cantiello

We present HST/STIS time-series spectroscopy of the central star of the "Cat's Eye" planetary nebula NGC 6543. Intensive monitoring of the UV lines over a 5.8 hour period reveals well defined details of large-scale structure in the fast wind, which are exploited to provide new constraints on the rotation rate of the central star. We derive characteristics of the line profile variability that support a physical origin due to co-rotating interaction regions (CIRs) that are rooted at the stellar surface. The recurrence time of the observed spectral signatures of the CIRs is used to estimate the rotation period of the central star and, adopting a radius between 0.3 and 0.6 solar radii constrains the rotational velocity to the range 54 \leq v_{rot} \leq 108 \kms. The implications of these results for single star evolution are discussed based on models calculated here for low-mass stars. Our models predict a sub-surface convective layer in NGC 6543 which we argue to be causally connected to the occurrence of structure in the fast wind.

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NGC 6543
Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI
JPEG (391 kb) Tiff (9.3 MB) PS (7.8 MB)

This composite of data from NASA's Chandra X-ray Observatory and Hubble Space Telescope is a new look for NGC 6543, better known as the Cat's Eye nebula. This famous object is a so-called planetary nebula that represents a phase of stellar evolution that the Sun should experience several billion years from now. When a star like the Sun begins to run out of fuel, it becomes what is known as a red giant. In this phase, a star sheds some of its outer layers, eventually leaving behind a hot core that collapses to form a dense white dwarf star. A fast wind emanating from the hot core rams into the ejected atmosphere, pushes it outward, and creates the graceful filamentary structures seen with optical telescopes.

Position (2000): RA 17h 58m 33.30s | Dec +66'° 37' 59.20"

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