THECHANDRAX-RAY SURVEY OF PLANETARY NEBULAE (CHANPLANS): PROBING BINARITY, MAGNETIC FIELDS, AND WIND COLLISIONS

Abstract

We present an overview of the initial results from the Chandra Planetary Nebula Survey (ChanPlaNS), the first systematic (volume-limited) Chandra X-Ray Observatory survey of planetary nebulae (PNe) in the solar neighborhood. The first phase of ChanPlaNS targeted 21 mostly high-excitation PNe within ∼1.5 kpc of Earth, yielding four detections of diffuse X-ray emission and nine detections of X-ray-luminous point sources at the central stars (CSPNe) of these objects. Combining these results with those obtained from Chandra archival data for all (14) other PNe within ∼1.5 kpc that have been observed to date, we find an overall X-ray detection rate of ∼70% for the 35 sample objects. Roughly 50% of the PNe observed by Chandra harbor X-ray-luminous CSPNe, while soft, diffuse X-ray emission tracing shocks-in most cases, "hot bubbles"-formed by energetic wind collisions is detected in ∼30%; five objects display both diffuse and point-like emission components. The presence (or absence) of X-ray sources appears correlated with PN density structure, in that molecule-poor, elliptical nebulae are more likely to display X-ray emission (either point-like or diffuse) than molecule-rich, bipolar, or Ring-like nebulae. All but one of the point-like CSPNe X-ray sources display X-ray spectra that are harder than expected from hot (∼100 kK) central stars emitting as simple blackbodies; the lone apparent exception is the central star of the Dumbbell nebula, NGC 6853. These hard X-ray excesses may suggest a high frequency of binary companions to CSPNe. Other potential explanations include self-shocking winds or PN mass fallback. Most PNe detected as diffuse X-ray sources are elliptical nebulae that display a nested shell/halo structure and bright ansae; the diffuse X-ray emission regions are confined within inner, sharp-rimmed shells. All sample PNe that display diffuse X-ray emission have inner shell dynamical ages 5 × 10 3 yr, placing firm constraints on the timescale for strong shocks due to wind interactions in PNe. The high-energy emission arising in such wind shocks may contribute to the high excitation states of certain archetypical "hot bubble" nebulae (e.g., NGC 2392, 3242, 6826, and 7009).

UNBIASED MILLIMETER-WAVE LINE SURVEYS OF TW Hya AND V4046 Sgr: THE ENHANCED C2H AND CN ABUNDANCES OF EVOLVED PROTOPLANETARY DISKS

“…Both protostars are classified as hot corinos, that is, protostellar envelopes that are particularly chemically active due to strong heating from accretion processes and/or external radiation fields (e.g., Bottinelli et al 2007;Watanabe et al 2012). Table 6 also includes fractional molecular abundances measured for the planetary nebula NGC 7027, which features strong stellar UV and nebular X-ray radiation fields (see, e.g., Kastner et al 2012). …”

Extended Structures of Planetary Nebulae Detected in H2 Emission∗

“…These radial rays are not quite obvious in the H 2 image of NGC 6781 but are visible in its residual H 2 image (see Figure 15). The fact that no X-ray emission was detected in these three PNe by Chandra (Kastner et al 2012) also indicates that the stellar winds from their central stars had probably already declined.…”

CONSTRAINTS ON THE SURFACE MAGNETIC FIELDS AND AGE OF A COOL HYPERGIANT:XMM-NEWTONX-RAY OBSERVATIONS OF VY CMa

“…The field of the XMM-Newton EPIC-pn observation analyzed in this paper is indicated. Kastner et al 2012;Freeman et al 2014;Montez & ChanPlaNS Collaboration 2014).…”