[Fe IV] in the Orion Nebula

Authors

R. H. Rubin, NASA/Ames Research Center
R. J. Dufour, Rice University
Gary J. Ferland, University of KentuckyFollow
P. G. Martin, University of Toronto, Canada
C. R. O'Dell, Rice University
J. A. Baldwin, Cerro Tololo Inter-American Observatory, Chile
J. J. Hester, Arizona State University
D. K. Walter, South Carolina State University
Z. Wen, Rice University

Abstract

Using the Goddard High-Resolution Spectrograph on the Hubble Space Telescope, we measured the flux of [Fe IV] (3d^{5 4}P_5/2 --> 3d^{5 6}S_5/2) λ_vac = 2836.56 Å in the Orion Nebula, the first detection of an [Fe IV] line in an H II region. A useful upper limit is set on the sum of fluxes of [Fe IV] (3d^{5 4}D_{5/2, 3/2} --> 3d^{5 6}S_5/2) λ_vac = 2568.4, 2568.2 Å. By comparing these observations with predicted fluxes from simply ``retrofitting'' our two previous photoionization models, we are able to derive (or set an upper limit on) the Fe/H abundance ratio: 70, 200 times lower than solar from the 2837 Å line, and ≥38, ≥120 times lower than solar from the 2568 Å line limit. If collisional excitation from the ground state were indeed the dominant mechanism for populating the respective upper levels of these lines, then the inferred Fe/H from the 2837 Å line and limit from the 2568 Å line would be ~3.0 and ~3.4 times larger than above. All these ratios are much lower than several recent determinations of gas-phase Fe/H ~ 3 × 10^-6 in Orion, which themselves are a factor ~10 depleted relative to solar. Because the inferred Fe/H should be at least as high in the Fe⁺³ zone as in the Fe⁺ and Fe⁺² zones, a reexamination of the Fe⁺³ atomic data and improved modeling would be valuable. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by AURA, Inc., under NASA contract NAS5-26555.

Document Type

Article

Publication Date

1-10-1997

Notes/Citation Information

Published in The Astrophysical Journal Letters, v. 474, no. 2, p. L131-L134.

© 1997. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

The copyright holder has granted permission for posting the article here.

Digital Object Identifier (DOI)

http://dx.doi.org/10.1086/310437

Repository Citation

Rubin, R. H.; Dufour, R. J.; Ferland, Gary J.; Martin, P. G.; O'Dell, C. R.; Baldwin, J. A.; Hester, J. J.; Walter, D. K.; and Wen, Z., "[Fe IV] in the Orion Nebula" (1997). Physics and Astronomy Faculty Publications. 125.
https://uknowledge.uky.edu/physastron_facpub/125