Thermal dust emission from proplyds, unresolved disks, and shocks in the Orion Nebula

Nathan Smith, John Bally, Ralph Y. Shuping, Mark Morris, Marc Kassis

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


We present a new 11.7 μm mosaic image of the inner Orion Nebula obtained with the T-ReCS instrument on Gemini South. The map covers 2.′7 × 1.′6, with a diffraction-limited spatial resolution of 0.″35; it includes the BN/KL region, the Trapezium, and OMC-1 South. Excluding BN/KL, we detect 91 thermal-IR point sources, with 27 known proplyds and over 30 "naked" stars showing no extended structure in Hubble Space Telescope (HST) images. Within the region we surveyed, ∼80% of known proplyds show detectable thermal-IR emission, almost 40% of naked stars are detected at 11.7 μm, and the fraction of all visible sources with 11.7 μm excess emission (including both proplyds and stars with unresolved disks) is roughly 50%. These fractions exclude embedded sources. Thermal dust emission from stars exhibiting no extended structure in HST images is surprising and means that they have retained circumstellar dust disks comparable to the size of our solar system. Proplyds and stars with IR excess are not distributed randomly in the nebula; instead, they show a clear anticorrelation in their spatial distribution, with proplyds clustered close to θ1 Ori C and other IR sources found preferentially farther away. We suspect that the clustered proplyds trace the youngest ∼0.5 Myr age group associated with the Trapezium, while the more uniformly distributed sources trace the older 1-2 Myr population of the Orion Nebula Cluster. This suggests that small protoplanetary disks persist for a few million years in irradiated environments and hints that hierarchical subclustering has been important on ∼30″ scales around the Trapezium. We detect 11.7 μm emission from the five brightest members of the Trapezium (θ1 Ori A, B, C, D, and E), caused by free-free stellar wind emission and possibly emission from dusty disks around companion stars. Within 30″ of θ1 Ori C, 100% of known proplyds are detected at 11.7 μm, and they exhibit remarkable limb-brightened dust arcs at the collision of the proplyd mass loss and the wind from θ1 Ori C. The star θ1 Ori D is associated with the most prominent mid-IR dust arc of the Ney-Allen Nebula. We propose that this arc is the consequence of θ1 Ori D being the closest member of the Trapezium to the background cloud. Finally, we detect dust emission from Herbig-Haro jets in Orion, including HH 202, 529, 513, and 514. This is the first detection of mid-IR continuum emission from dust in the body of a collimated HH jet or bow shock. The presence of dust implies that some jet material must be lifted from large radii in the accretion disk (outside the dust sublimation radius) or entrained from the circumstellar environment.

Original languageEnglish (US)
Pages (from-to)1763-1777
Number of pages15
JournalAstronomical Journal
Issue number4
StatePublished - Oct 2005


  • H II regions
  • ISM: Herbig-Haro objects
  • ISM: jets and outflows
  • Planetary systems: protoplanetary disks
  • Stars: formation
  • Stars: pre-main-sequence

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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