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Far infrared spectroscopy of FU Ori objects. ISO-LWS observations

Lorenzotti, D.; Giannini, T.; Nisini, B.; Benedettini, M.; Creech-Eakman, M.; Blake, G. A.; van Dishoeck, E. F.; Cohen, M.; Liseau, R.; Molinari, S.; Pezzuto, S.; Saraceno, P.; Smith, H. A.; Spinoglio, L. and White, G. J. (2000). Far infrared spectroscopy of FU Ori objects. ISO-LWS observations. Astronomy & Astrophysics, 357 pp. 1035–1044.

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Abstract

We present the results of the first spectrophotometric observations of a sample of FU Ori objects obtained with the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). The [OI] (63 μm) and the [CII] (158 μm) lines are commonly observed in all spectra (both ON and OFF source). The observational novelty is the presence in most of the sources of the transition of ionised nitrogen [NII] (122 μm), which is not detected in other objects in a similar evolutionary phase. This line probes low ionisation and low density material not easily traced by other lines. Line intensities and intensity ratios are used along with model predictions to infer the prevailing mechanisms for line excitation. To reconcile our far-infrared spectroscopy with previous knowledge of these objects, the simultaneous presence of two components is required: well localised J-shocks, responsible for the [OI] emission, and an extended low density ionised medium produced by UV photons from the disc boundary layer, responsible for the [NII] and [CII] emission. A few molecular lines (CO, OH, H2O) associated with relatively cold and dense peaks are revealed and their intensities are in good agreement with the proposed scenario. Other ionic lines ([OIII] and [NIII]) are detected in two sources in the Cyg OB7 region and likely trace the presence of nearby HII regions.

Item Type: Journal Article
Copyright Holders: 2000 ESO
ISSN: 1432-0746
Keywords: stars; circumstellar matter
Academic Unit/Department: Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
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Item ID: 32657
Depositing User: Glenn White
Date Deposited: 23 Feb 2012 14:37
Last Modified: 18 Oct 2014 20:22
URI: http://oro.open.ac.uk/id/eprint/32657
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