The Infrared Emission of Circumstellar Envelopes, Dark Silhouettes and Photoionized Disks in HII Regions

Abstract

We model the IR Spectral Energy Distribution of circumstellar disks embedded in a HII region and photoevaporated by the external UV radiation. The model applies to the photoevaporated disks (proplyds) in Orion Nebula. First we calculate the IR emission of a PMS star surrounded by a dusty globule that is immersed within an HII region. The globule is assumed to be spherical, homogeneous, optically thin in the IR and photoevaporated according to the Dyson (1968) model. Second, we consider the IR emission of a disk directly exposed to the nebular environment. The disk is passive and treated according to the Chiang and Goldreich (1997) model. We improve over the CG97 treatment by tracing the propagation of the various radiative fluxes through the disk superheated atmosphere. Since the opposite disk sides receive different amounts of radiation, the flaring angle and the surface temperature distributions are different, resulting in well distinguished SEDs for the two disk faces. Finally, we combine the globule and disk models to estimate the IR emission of proplyds. The energy input from the central star and the nebular environment increase the disk flaring angle, and therefore also the amount of stellar radiation intercepted by the disk. The relative intensity of the disk vs. envelope emission varies with the tilt angle relative to the directions of th1Ori-C, and of the Earth. We explore the dependence of the SEDs upon the tilt angle with respect to the Earth, the distance from th1Ori-C, the size on the envelope, the inner disk radius and the temperature of the central star. The resulting SEDs are characterized by a broad peak of emission at 30-60micron, and are in general significantly different from those of isolated disks in low-mass star forming regions like Taurus-Auriga.

arXiv comment29 pages + 22 figures, in press on ApJ, v578 n2, October 2002

References in corpus (2)

• Spectral Energy Distributions of T Tauri Stars With Passive Circumstellar Disks
• High-resolution near-infrared imaging of the Orion 114-426 silhouette disk

Cited by in corpus (22)

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• The VLTI/MIDI survey of massive young stellar objects - Sounding the inner regions around intermediate- and high-mass young stars using mid-infrared interferometry
• The Orion Nebula in the mid-IR
• Dead Zones and Extrasolar Planetary Properties
• Dead Zones and the Origin of Planetary Masses
• The Growth & Migration of Jovian Planets in Evolving Protostellar Disks with Dead Zones
• A Wide-Field Survey of the Orion Nebula Cluster in the Near-Infrared
• HST/WFPC2 Study of the Trapezium Cluster: the Influence of Circumstellar Disks on the Initial Mass Function
• Photoevaporation and spatial variation of grain sizes in Orion 114-426
• High-Resolution Infrared Imaging of Herschel 36 SE: A Showcase for the Influence of Massive Stars in Cluster Environments
• The extinction map of the OMC-1 molecular cloud behind the Orion Nebula
• Ionized gas diagnostics from protoplanetary discs in the Orion Nebula and the abundance discrepancy problem
• Warm millimetre dust in protoplanetary discs near massive stars
• Silicate Emission Profiles from Low-Mass Protostellar Disks in the Orion Nebula: Evidence for Growth and Thermal Processing of Grains
• Chemical abundances in Orion protoplanetary discs: integral field spectroscopy and photoevaporation models of HST 10
• Rotational Instability in the Outer Region of Protoplanetary Disks
• Evidence for a Photoevaporated Circumbinary Disk in Orion
• First Science Observations with SOFIA/FORCAST: 6 to 37 micron Imaging of the Central Orion Nebula
• Near-infrared polarization images of the Orion proplyds