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Ionization fronts and shocked flows - The structure of the Orion Nebula at 0".1

Hester, J. Jeff and Gilmozzi, R. and O'Dell, C. R. and Faber, S. M. and Campbell, Bel and Code, Arthur and Currie, Douglas G. and Danielson, G. Edward and Ewald, S. P. and Groth, Edward J. and Holtzman, Jon A. and Kelsall, T. and Lauer, Tod R. and Light, Robert M. and Lynds, Roger and O'Neill, Earl J., Jr. and Shaya, Edward J. and Westphal, James A. (1991) Ionization fronts and shocked flows - The structure of the Orion Nebula at 0".1. Astrophysical Journal Letters, 369 (2). L75-L78. ISSN 2041-8205. doi:10.1086/185962.

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We present HST Wide-Field Camera images of a field in the Orion Nebula obtained in emission from [S II], Hβ, and [O II]. The morphology of the [S II] emission is markedly different from the other lines. While Hβ and [O II] are distributed fairly smoothly, [S II] is dominated by filamentary features with widths between 0".1 and 1" which sharply highlight ionization fronts moving into dense neutral material. These photoionization fronts act as probes of the structure of the cavity walls of this blister H II region. Their morphology indicates that while the surfaces into which they are moving are textured, subarcsecond clumps with high density contrast are uncommon. An exception is a bow shock-shaped ionization front seen along the face of a solar system-sized (0".6 = 270 AU) clump which is itself seen in extinction. The field contains a number of HH objects and related structures, many of which were previously recognized as such, but whose complex structure is revealed here by the resolution of HST. These include M42 HH 1, which is seen to be an intricate structure of knots and filaments with a head-tail morphology. M42 HH 2 shows structure from both the shocked cavity walls and the shocked atomic outflow. M42 HH 5-7 break into numerous condensations with an appearance reminiscent of HH 7-11. All objects with a bow shockshaped structure (i.e., M42 HH 1, 5, 7, and 10) show enhanced Hβ emission at the apex of the structure where the shock should be strongest. M42 HH 8 and 9 may be HH objects viewed face-on, or alternatively condensations photoionized by a nearby A or B star. Emission from [S II] traces shocks at the walls of an ionized jet apparently emanating from a star in a dark cloud. This cloud seen in extinction is coincident with H_2 Peak 1, which we propose is on the near side of the nebula.

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Faber, S. M.0000-0003-4996-214X
Ewald, S. P.0000-0002-1567-9154
Additional Information:© 1991 American Astronomical Society. Provided by the NASA Astrophysics Data System. Received 1990 October 17; accepted 1990 November 14. J. J. H. would like to acknowledge numerous conversations on the structure of H II regions with R. J. Dufour and R. A. R. Parker, and with K. Stapelfeldt and J. Raymond on the structure of HH objects. J. J. H. acknowledges support from NASA and CIT through IPAC. The WF/PC IDT is supported by NASA contract NAS5-25451.
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Subject Keywords:nebulae: Orion Nebula, nebulae: structure, stars: formation
Issue or Number:2
Record Number:CaltechAUTHORS:20141126-100020453
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Official Citation:Ionization fronts and shocked flows - The structure of the Orion Nebula at 0."1 Hester, J. Jeff; Gilmozzi, R.; O'dell, C. R.; Faber, S. M.; Campbell, Bel; Code, Arthur; Currie, Douglas G.; Danielson, G. Edward; Ewald, S. P.; Groth, Edward J.; Holtzman, Jon A.; Kelsall, T.; Lauer, Tod R.; Light, Robert M.; Lynds, Roger; O'Neil, Earl J., Jr.; Shaya, Edward J.; Westphal, James A. Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 369, March 10, 1991, p. L75-L78.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52173
Deposited By: Ruth Sustaita
Deposited On:26 Nov 2014 19:10
Last Modified:10 Nov 2021 19:22

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