High spatial/spectral resolution x-ray observations and volumetric 3d modeling of superheated plasma in the planetary nebula BD+30◦3639

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Title: High spatial/spectral resolution x-ray observations and volumetric 3d modeling of superheated plasma in the planetary nebula BD+30◦3639
Author: Yu, Young Sam
Abstract: Planetary nebulae (PNs) represent the last dying stages of evolution for sun-like stars. Though astronomers have traditionally studied PNs in optical emission lines, which mainly probe UV-photoionized gas, the study of X-ray emission from PNs offers insight into much more energetic process associated with stellar death. I present and analyze the results of multiple Chandra X-ray observations of the X-ray-bright, young PN BD+30°3639. The Chandra datasets analyzed include a 3.5-day gratings spectroscopy observation for a total of 300 ks exposure and two direct CCD imaging observations. This thesis is based primarily on a detailed spatial/spectral analysis of the gratings data. Modeling of this gratings spectrum indicates the presence of a range of plasma temperatures from Tx ~1.7 × 106 K to 2.9 × 106 K and conclusively demonstrates that C and Ne are highly enhanced, while N and Fe are depleted. These results are generally consistent with earlier results obtained from X-ray CCD imaging spectroscopy of BD+30°3639, but are far more precise. I obtained a direct Chandra CCD image in 2009 to compare with the Chandra CCD image obtained in 2000 and thereby to test the hypothesis that the X-ray emission could be due to fast-expanding jets. The error normalized difference image (2009 - 2000) does not reveal an apparent expansion signature, and comparison of flux images does not show any significant change in surface brightness over the 9 year span, indicating that the X-rays are generated by a quasi-spherical wind from the present-day central star. I argue that an exponential decline in flux below ~1 keV is caused by the contamination of the CCD imaging detector rather than a real decline in flux from the PN, and suggest that BD+30°3639 is a good candidate for the long-term calibration of this Chandra instrument. I construct 3-dimensional plasma models to describe the intrinsic structure of the X-ray-emitting region of BD+30°3639 by reproducing the grating spectroscopy results (both the 0th order image and dispersed images), taking into account the physical/chemical plasma components and intervening absorption obtained from spectral model fitting and Chandra's instrumental characteristics. This approach takes advantage of volumetric 3D modeling (V3D) routines under development at MIT's Kavli Institute. I present results in the form of X-ray spectra and images synthesized using spectral-V3D models. I outline how these studies of BD+30°3639 serve to constrain models of stellar evolution and PN morphologies and to guide the development of sophisticated models of the wind interactions responsible for the superheated gas within PNs.
Record URI: http://hdl.handle.net/1850/11193
Date: 2009-11

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