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The molecular cloud core M 17-North: ISO spectroscopy and IR/mm continuum mapping *
Th. Henning 1,
R. Klein 1,
R. Launhardt 1,
D. Lemke 2 and
W. Pfau 1
Received 21 July 1997 / Accepted 5 January 1998
We present the first complete infrared spectrum of a molecular cloud core covering the wavelength region from 2.4 up to 200 µm together with a map at 1.3 mm wavelength and near-infrared (NIR) images. The core is located in the northern part of M 17 and shows strong evidence for on-going star formation. These data are the first step towards a complete characterization of M 17-North .
The spectrum has been obtained with the Infrared Space Observatory (ISO) using the short- and long-wavelength spectrometers (SWS/LWS) with a resolution from 150 to 300. The spectrum of the core displays the unidentified infrared bands (UIBs). The continuum is rising rapidly for wavelengths larger than 15 µm which is typical for objects with stronger UV radiation fields. This continuum is probably produced by the emission from very small grains (VSGs) heated transiently.
Many low-excitation fine structure lines were detected which are typical for the emission from an H II region. They are produced by an electron gas with a density and temperature of about 100 cm-3 and 5000 K, respectively.
The mapping of the continuum radiation at 1.3 mm revealed the presence of a compact cloud core, whereas NIR imaging led to the detection of embedded IR objects. The observed spectral energy distribution (SED) is used to model the cloud core emission with radiative transfer (RT) calculations including the emission from VSGs. This calculation shows that the cloud core is mainly heated by an outer radiation field but needs an additional inner heating source with a luminosity of about 8000 to explain the measurements.
Key words: ISM: clouds dust, extinction ISM: individual objects: M 17N infrared: ISM: continuum infrared: ISM: lines and bands radio continuum: ISM
* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA
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© European Southern Observatory (ESO) 1998
Online publication: March 30, 1998