A Caltech Library Service

A search for temperature and density variations in NGC 7027 with the Hubble Space Telescope

Bieging, John H. and Boley, Paul A. and Latter, William B. and Tielens, A. G. G. M. (2008) A search for temperature and density variations in NGC 7027 with the Hubble Space Telescope. Astrophysical Journal, 676 (1). pp. 390-401. ISSN 0004-637X.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


We observed the young planetary nebula NGC 7027 with the HST Imaging Spectrograph (STIS) in long-slit mode at five slit positions along the major axis of the nebula, over the wavelength range from 3000 to ~10,000 Å. We used dereddened line ratios to determine line-of-sight average values for (1) He^(++) and He^+ ionization fractions from He II λ4686 and He I λ5876; (2) electron density from both [S II] (λ6716/λ6731) and [Ar IV] (λ4711/λ4740); and (3) temperature from [O III] (λ4959 + λ5007)/λ4363. The He^(++)/H^+ ratio varies across the nebula, with values up to 0.06 over the central parts, falling off to 0.03 at offsets of 5"-6" from the central star. The line-of-sight mean densities vary by factors of ~5 on angular scales as small as ~1". The average electron temperatures are generally consistent with a constant < T_e > = 13,800 ± 2000 K within the uncertainties, except for ~2% of measured pixels where T_e > 18,000 K. The variations of density along the slits are not obviously correlated with variations in extinction. The ionization structure of the nebula varies on both large and small scales. [O I] λ6300, Hα, and He II λ4686 intensity profiles along each slit appear to trace ionization gradients at Hα peaks, with the highest ionization on the side toward the central star and lowest ionization on the far side. These structures may result from effects of stellar radiation, shocks from a fast stellar wind, or some combination of the two processes.

Item Type:Article
Related URLs:
URLURL TypeDescription
Additional Information:© 2008 The American Astronomical Society. Received 2007 June 14, accepted for publication 2007 December 13. We thank Indra Bains for providing her emission measure map in digital form, and Don Garnett for helpful discussions. Support for proposal number GO-08285 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. This work was supported in part by National Science Foundation grant AST-0307687 to The University of Arizona.
Funding AgencyGrant Number
Subject Keywords:atomic processes; planetary nebulae: general; planetary nebulae: individual (NGC 7027)
Issue or Number:1
Record Number:CaltechAUTHORS:BIEapj08
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13273
Deposited By: Tony Diaz
Deposited On:14 Jul 2009 17:26
Last Modified:03 Oct 2019 00:35

Repository Staff Only: item control page