Bibcode
De Marco, O.; Chu, Y.-H.; Steffen, M.; Sokoloski, J. L.; Soker, N.; Schönberner, D.; Sandin, C.; Parker, Q. A.; Nordhaus, J.; Bujarrabal, V.; Corradi, R. L. M.; Zijlstra, A.; Behar, E.; Lopez, J. A.; Rapson, V.; Frank, A.; Guerrero, M. A.; Blackman, E.; Sahai, R.; Miszalski, B.; Frew, D. J.; Balick, B.; Montez, R., Jr.; Kastner, J. H.; Villaver, E.; Ueta, T.
Referencia bibliográfica
The Astronomical Journal, Volume 144, Issue 2, article id. 58 (2012).
Fecha de publicación:
8
2012
Número de citas
107
Número de citas referidas
79
Descripción
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 × 103 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).
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Antonio
Mampaso Recio