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

Abstract

We present X-ray spectral analysis of 20 point-like X-ray sources detected in\nChandra Planetary Nebula Survey (ChanPlaNS) observations of 59 planetary\nnebulae (PNe) in the solar neighborhood. Most of these 20 detections are\nassociated with luminous central stars within relatively young, compact\nnebulae. The vast majority of these point-like X-ray-emitting sources at PN\ncores display relatively "hard" ($\\geq0.5$~keV) X-ray emission components that\nare unlikely to be due to photospheric emission from the hot central stars\n(CSPN). Instead, we demonstrate that these sources are well modeled by\noptically-thin thermal plasmas. From the plasma properties, we identify two\nclasses of CSPN X-ray emission: (1) high-temperature plasmas with X-ray\nluminosities, $L_{\\rm X}$, that appear uncorrelated with the CSPN bolometric\nluminosity, $L_{\\rm bol}$; and (2) lower-temperature plasmas with $L_{\\rm\nX}/L_{\\rm bol}\\sim10^{-7}$. We suggest these two classes correspond to the\nphysical processes of magnetically active binary companions and self-shocking\nstellar winds, respectively. In many cases this conclusion is supported by\ncorroborative multiwavelength evidence for the wind and binary properties of\nthe PN central stars. By thus honing in on the origins of X-ray emission from\nPN central stars, we enhance the ability of CSPN X-ray sources to constrain\nmodels of PN shaping that invoke wind interactions and binarity.\n