The Enigmatic X-Ray Point Sources at the Central Stars of NGC 6543 and NGC 7293

Vrtilek

et al. 2002

ApJ

Chandra X-Ray Observatory (CXO) images have revealed that the X-ray-emitting regions of the moleculerich young planetary nebulae (PNe) BD +30 3639 and NGC 7027 are much more asymmetric than their optical nebulosities. To evaluate the potential origins of these X-ray asymmetries, we analyze X-ray images of BD +30 3639, NGC 7027, and another PN resolved by CXO, NGC 6543, within specific energy bands. Image resolution has been optimized by subpixel repositioning of individual X-ray events. The resulting subarcsecond resolution images reveal that the soft (E < 0:7 keV) X-ray emission from BD +30 3639 is more uniform than the harder emission, which is largely confined to the eastern rim of the optical nebula. In contrast, soft X-rays from NGC 7027 are highly localized and this PN is more axially symmetric in harder emission. The broadband X-ray morphologies of BD +30 3639 and NGC 7027 are highly anticorrelated with their distributions of visual extinction, as determined from high-resolution, space-and ground-based optical and infrared imaging. Hence, it is likely that the observed X-ray asymmetries of these nebulae are due in large part to the effects of nonuniform intranebular extinction. However, the energy-dependent X-ray structures in both nebulae and NGC 6543-which is by far the least dusty and molecule-rich of the three PNe and displays very uniform intranebular extinction-suggest that other mechanisms, such as the action of collimated outflows and heat conduction, are also important in determining the detailed X-ray morphologies of young PNe.

Section: No 2 2002 Extended X-ray Emission From Pnesupporting

confidence: 88%

On the Asymmetries of Extended X‐Ray Emission from Planetary Nebulae

Vrtilek

et al. 2002

ApJ

“…Our spectral fit for NGC 7293 is very similar to that of Guerrero et al (2001), but we note that, in these best-fit models, there are significant discrepancies between the model and data near 1 keV. These discrepancies may suggest the presence of multi-temperature components and/or emission lines (Soker & Kastner 2002).…”

Section: The Central Star Of the Helix Nebulasupporting

confidence: 57%

THE CHANDRA PLANETARY NEBULA SURVEY (ChanPlaNS). III. X-RAY EMISSION FROM THE CENTRAL STARS OF PLANETARY NEBULAE

Montez

Balick

et al. 2015

ApJ

We present X-ray spectral analysis of 20 point-like X-ray sources detected in Chandra Planetary Nebula Survey observations of 59 planetary nebulae (PNe) in the solar neighborhood. Most of these 20 detections are associated with luminous central stars within relatively young, compact nebulae. The vast majority of these point-like X-rayemitting sources at PN cores display relatively "hard" ( 0.5 keV) X-ray emission components that are unlikely to be due to photospheric emission from the hot central stars (CSPN). Instead, we demonstrate that these sources are well modeled by optically thin thermal plasmas. From the plasma properties, we identify two classes of CSPN X-ray emission: (1) high-temperature plasmas with X-ray luminosities, L X , that appear uncorrelated with the CSPN bolometric luminosity, L bol and (2) lower-temperature plasmas with L X /L bol ∼ 10 −7 . We suggest these two classes correspond to the physical processes of magnetically active binary companions and self-shocking stellar winds, respectively. In many cases this conclusion is supported by corroborative multiwavelength evidence for the wind and binary properties of the PN central stars. By thus honing in on the origins of X-ray emission from PN central stars, we enhance the ability of CSPN X-ray sources to constrain models of PN shaping that invoke wind interactions and binarity.

“…Absorption will preferentially attenuate the soft portion of the X-ray spectrum, hence drastically reducing or eliminating the soft photospheric signature; furthermore, a large absorbing column can reduce the hard (>0.6 keV) X-ray flux below the detection threshold. Nevertheless, many (∼13) hard X-ray emitting CSPNe have been reported in early Chandra observations (Guerrero et al 2001), in binary CSPNe (Montez et al 2010), and in the Chandra Planetary Nebulae Survey (ChanPlaNS; Kastner et al 2012). Our modeling of the CSPN of K 1-16 suggests that this hard X-ray emission may be explained by photospheric emission, plasma emission, or a combination of both.…”

Section: Discussionmentioning

confidence: 70%

Serendipitous Detection of X-Ray Emission From the Hot Born-Again Central Star of the Planetary Nebula K 1-16

Montez

2013

ApJ

We report the serendipitous detection of point-like X-ray emission from the hot, PG1159-type central star of the planetary nebula (CSPN) K 1-16 by the XMM-Newton and Chandra X-Ray Observatories. The CSPN lies superimposed on a galaxy cluster that includes an X-ray-bright quasar, but we have successfully isolated the CSPN X-ray emission from the strong diffuse background contributed by the quasar and intracluster gas. We have modeled the XMM-Newton and Chandra X-ray data, taking advantage of the contrasting detection efficiencies of the two observatories to better constrain the low-energy spectral response of Chandra's Advanced CCD Imaging Spectrometer. We find that the CSPN X-ray spectrum is well characterized by the combination of a non-local thermodynamic equilibrium model atmosphere with T ∼ 135 kK and a carbon-rich, optically thin thermal plasma with T X ∼ 1 MK. These results for X-ray emission from the K 1-16 CSPN, combined with those obtained for other PG1159-type objects, lend support to the "born-again" scenario for Wolf-Rayet and PG1159 CSPNe, wherein a late helium shell flash dredges up carbon-rich intershell material and ejects this material into the circumstellar environment.