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          Institute: MPI für extraterrestrische Physik     Collection: Infrared and Submillimeter Astronomy     Display Documents

ID: 13522.0, MPI für extraterrestrische Physik / Infrared and Submillimeter Astronomy
The photoionization of a star-forming core in the Trifid Nebula
Authors:Le Floch, B.; Cernicharo, J.; Rodriguez, L. F.; Miville-Deschenes, M. A.; Cesarsky, D.; Heras, A.
Date of Publication (YYYY-MM-DD):2002-12-10
Title of Journal:The Astrophysical Journal
Journal Abbrev.:Astrophys. J.
Issue / Number:1
Start Page:335
End Page:356
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We have carried out a comprehensive multiwavelength study of the bright-rimmed globule TC2 in the Trifid Nebula, using the IRAM 30 m telescope, the VLA centimeter array, and the Infrared Space Observatory (ISO). TC2 is one of the very few globules to exhibit signs of active ongoing star formation while being photoevaporated by the Lyman continuum flux of the exciting star of the nebula (similar to10(10) cm(-2) s(-1)). The globule consists of a cold dense core of mass 27 M-circle dot surrounded by a lower density envelope of molecular gas. The impinging Lyman continuum photons induce the propagation of an ionization front into the globule. The evaporation of the ionized gas forms a thin layer of density n(e)=(1-2)x10(3) cm(- 3) around the globule, which could be mapped with the VLA. The globule is illuminated mainly on its rear side, by a far- ultraviolet field of intensity G(0)similar or equal to1000. It creates a photon-dominated region (PDR) below the surface, which was mapped and characterized with the ISOCAM circular variable filter and the Short Wavelength Spectrometer (SWS) on board ISO. The physical conditions derived from the analysis of the far-infrared lines [O I] 63, 145 mum and [C II] 158 mum and the continuum emission are in good agreement with some recent PDR models. The emission of the polycyclic aromatic hydrocarbon band at 6.2, 7.7, 8.6, and 11.3 mum is detected over the whole globule. The relative intensity variations observed across the globule, in the PDR and the photoionized envelope, are consistent with the changes in the ionization fraction. In the head of TC2, we find a second kinematic component, which is the signature of the radiatively driven collapse undergone by the globule. This component indicates that the PDR propagates at low velocity inside the body of TC2. The molecular emission suggests that the star formation process was probably initiated a few times 10(5) years ago, in the large burst that led to the formation of the nebula. The globule has already evaporated half the mass of its envelope. However, the ionization timescale of the globule is long enough (similar to2 Myr) to let the protostellar objects reach smoothly the ultimate stages of protostellar evolution. The impact of photoionization on the star formation process appears limited
Free Keywords:dust; extinction; HII regions; ISM : globules; ISM : individual (Trifid Nebula); ISM : jets and outflows; stars : formation
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für extraterrestrische Physik
External Affiliations:Observ Grenoble, Astrophys Lab, BP 53, F-38041 Grenoble 9,; France; Observ Grenoble, Astrophys Lab, F-38041 Grenoble 9, France; CSIC, Inst Estructura Mat, E-28006 Madrid, Spain; Univ Nacl Autonoma Mexico, Inst Astron, Morelia 58089, Michoacan, Mexico; Ecole Normale Super, Dept Phys, Lab Radioastron, F-75231 Paris, France; Max Planck Inst Extraterr Phys, D-85741 Garching, Germany; European Space Agcy, ESTEC, SCI SAF, NL-2200 AG Noordwijk, Netherlands
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