Near-infrared spectroscopy of (proto)-planetary nebulae: Molecular hydrogen excitation as an evolutionary tracer

Davis, C.J. and Smith, M.D. and Stern, L. and Kerr, T.H. and Chiar, J.E. (2003) Near-infrared spectroscopy of (proto)-planetary nebulae: Molecular hydrogen excitation as an evolutionary tracer. Monthly Notices of the Royal Astronomical Society, 344 (1). pp. 262-282. ISSN 0035-8711. (doi:https://doi.org/10.1046/j.1365-8711.2003.06820.x) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided. (Contact us about this Publication)
Official URL
http://dx.doi.org/10.1046/j.1365-8711.2003.06820.x

Abstract

We present an in-depth analysis of molecular excitation in 11 H 2-bright planetary and protoplanetary nebulae (PN and PPN). From newly acquired K-band observations, we extract a number of spectra at positions across each source. H2 line intensities are plotted on 'column density ratio' diagrams so that we may examine the excitation in and across each region. To achieve this, we combine the shock models of Smith, Khanzadyan & Davis with the photodissociation region (PDR) models of Black & van Dishoeck to yield a shock-plus-fluorescence fit to each data set. Although the combined shock + fluorescence model is needed to explain the low- and high-energy H2 lines in most of the sources observed (fluorescence accounts for much of the emission from the higher-energy H2 lines), the relative importance of shocks over fluorescence does seem to change with evolutionary status. We find that shock excitation may well be the dominant excitation mechanism in the least evolved PPN (CRL 2688 - in both the bipolar lobes and in the equatorial plane) and in the most evolved PN considered (NGC 7048). Fluorescence, on the other hand, becomes more important at intermediate evolutionary stages (i.e. in 'young' PN), particularly in the inner core regions and along the inner edges of the expanding post- asymptotic giant branch (AGB) envelope. Since H2 line emission seems to be produced in almost all stages of post-AGB evolution, H2 excitation may prove to be a useful probe of the evolutionary status of PPN and PN alike. Moreover, shocks may play an important role in the molecular gas excitation in (P)PN, in addition to the low- and/or high-density fluorescence usually attributed to the excitation in these sources.

Item Type: Article
Uncontrolled keywords: Circumstellar matter, Infrared: Stars, ISM: Jets and outflows, ISM: Kinematics and dynamics ISM: Lines and bands
Subjects: Q Science > QB Astronomy > QB460 Astrophysics
Divisions: Faculties > Sciences > School of Physical Sciences > Centre for Astrophysics and Planetary Sciences
Depositing User: Giles Tarver
Date Deposited: 11 Aug 2015 09:56 UTC
Last Modified: 12 Aug 2015 14:14 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/50126 (The current URI for this page, for reference purposes)
  • Depositors only (login required):