Structure and physical conditions in the Huygens region of the Orion nebula

C. R. O'Dell, G. J. Ferland, M. Peimbert

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


Hubble Space Telescope images, MUSE maps of emission lines, and an atlas of high velocity resolution emission-line spectra have been used to establish for the first time correlations of the electron temperature, electron density, radial velocity, turbulence, and orientation within the main ionization front of the nebula. From the study of the combined properties of multiple features, it is established that variations in the radial velocity are primarily caused by the photoevaporating ionization front being viewed at different angles. There is a progressive increase of the electron temperature and density with decreasing distance from the dominant ionizing star θ1 Ori C. The product of these characteristics (ne × Te) is the most relevant parameter in modelling a blister-type nebula like the Huygens region, where this quantity should vary with the surface brightness in Hα. Several lines of evidence indicate that smallscale structure and turbulence exist down to the level of our resolution of a few arcseconds. Although photoevaporative flow must contribute at some level to the well-known non-thermal broadening of the emission lines, comparison of quantitative predictions with the observed optical line widths indicates that it is not the major additive broadening component. Derivation of Te values for H+ from radio+optical and optical-only ionized hydrogen emission showed that this temperature is close to that derived from [N II] and that the transition from the well-known flat extinction curve which applies in the Huygens region to a more normal steep extinction curve occurs immediately outside of the Bright Bar feature of the nebula.

Original languageEnglish
Pages (from-to)4835-4857
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Feb 1 2017

Bibliographical note

Funding Information:
We are grateful to Wolfram Kollatschny, Peter Weilbacher, and the remainder of the MUSE team for creating the MUSE data base of Huygens region spectra and to William J. Henney for the processed GO-12543 data. Partial support for CRO's work was provided by HST grant GO 12543, whose original principal investigator was the late Robert H. Rubin. GJF acknowledges support by NSF (1108928, 1109061, and 1412155), NASA (10-ATP10-0053, 10-ADAP10-0073, and ATP13-0153), and STScI (HST-AR-13245, GO-12560, HST-GO-12309, GO-13310.002-A, HST-AR-13914, and HST-AR-14286.001).MP received partial support from CONACYT grant 241732. This paper benefitted in content and presentation from the comments of the referee.

Publisher Copyright:
© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


  • Dust
  • Extinction
  • H II regions
  • ISM: individual objects: Orion nebula (NGC 1976)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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