The Chandra Planetary Nebulae Survey (ChanPlaNS): III. X-ray Emission from the Central Stars of Planetary Nebulae

TL;DR

This study analyzes X-ray emissions from 20 central stars of planetary nebulae using Chandra data, identifying two main classes of X-ray sources linked to binary activity and stellar winds, which aids in understanding planetary nebula shaping.

Contribution

It classifies the X-ray emission mechanisms of CSPN into two categories and links them to physical processes like binarity and stellar winds, advancing knowledge of PN evolution.

Findings

Most X-ray sources are associated with luminous, young central stars.

X-ray emissions are modeled as optically-thin thermal plasmas, not photospheric.

Two classes of X-ray emission are identified: high-temperature plasma and wind-shock related.

Abstract

We present X-ray spectral analysis of 20 point-like X-ray sources detected in Chandra Planetary Nebula Survey (ChanPlaNS) 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-ray-emitting sources at PN cores display relatively "hard" ($\geq0.5$~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, $L_{\rm X}$, that appear uncorrelated with the CSPN bolometric luminosity, $L_{\rm bol}$; and (2) lower-temperature plasmas with $L_{\rm X}/L_{\rm bol}\sim10^{-7}$. 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.