ALMA Observations of Molecular Line Emission from High-excitation Bipolar Planetary Nebulae
arxiv(2024)
摘要
We present early results from our program of ALMA Band 6 (1.3mm) molecular
line mapping of a sample of nearby, well-studied examples of high-excitation,
bipolar/pinched-waist and molecule-rich planetary nebulae (Hubble 5 and NGC
2440, 2818, 2899, 6302, and 6445). We have mapped these planetary nebulae (PNe)
in isotopologues of CO as well as various molecular line tracers of high-energy
irradiation, such as HCN, CN, HNC, and HCO+, with the complementary goals of
establishing nebular kinematics as well as the zones of UV-heated and
X-ray-ionized molecular gas within each nebula. The resulting high-resolution
ALMA molecular emission-line maps reveal the regions of high-excitation bipolar
PNe in which molecular gas, presumably ejected during asymptotic giant branch
stages of the PN progenitor stars, survives and evolves chemically. We present
a summary of molecular species detected to date in the sample nebulae, and we
use example results for one PN (NGC 6455) to demonstrate the power of the ALMA
data in revealing the structures, kinematics, and compositions of the
equatorial molecular tori that are a common feature of the sample objects.
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