Mapping the Central Region of the PPN CRL 618 at Sub-arcsecond Resolution at 350 GHz

Abstract

CRL 618 is a well-studied pre-planetary nebula. We have mapped its central region in continuum and molecular lines with the Submillimeter Array at 350 GHz at ~ 0.3" to 0.5" resolutions. Two components are seen in 350 GHz continuum: (1) a compact emission at the center tracing the dense inner part of the H II region previously detected in 23 GHz continuum and it may trace a fast ionized wind at the base, and (2) an extended thermal dust emission surrounding the H II region, tracing the dense core previously detected in HC3N at the center of the circumstellar envelope. The dense core is dusty and may contain mm-sized dust grains. It may have a density enhancement in the equatorial plane. It is also detected in carbon chain molecules HC3N and HCN, and their isotopologues, with higher excitation lines tracing closer to the central star. It is also detected in C2H3CN toward the innermost part. Most of the emission detected here arises within ~ 630 AU (~0.7") from the central star. A simple radiative transfer model is used to derive the kinematics, physical conditions, and the chemical abundances in the dense core. The dense core is expanding and accelerating, with the velocity increasing roughly linearly from ~ 3 km/s in the innermost part to ~ 16 km/s at 630 AU. The mass-loss rate in the dense core is extremely high with a value of ~ 1.15x10^{-3} solar mass per year. The dense core has a mass of ~ 0.47 solar mass and a dynamical age of ~ 400 yrs. It could result from a recent enhanced heavy mass-loss episode that ends the AGB phase. The isotopic ratios of 12C/13C and 14N/15N are 9$\pm$4 and 150$\pm 50$, respectively, both lower than the solar values.

43 pages, 15 figures, Accepted by the ApJ

References in corpus (2)

• Preplanetary Nebulae: An HST Imaging Survey and a New Morphological Classification System
• A molecular line survey of the extreme carbon star CRL 3068 at millimeter wavelengths

Cited by in corpus (11)

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• The Shaping of the Multipolar Pre-Planetary Nebula CRL 618 by Multi-directional Bullets
• Steady Twin-Jets Orientation: Implications For Their Formation Mechanism
• Vibrationally Excited C${}_4$H
• The molecular envelope of CRL 618: A new model based on Herschel/HIFI observations
• Evolution from Spherical AGB Wind to Multipolar Outflow in Pre-Planetary Nebula IRAS 17150-3224
• Detection of 4765 MHz OH Emission in a Pre-Planetary Nebula -- CRL 618
• Post-AGB nebular studies