Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000a%26a...357.1035l&link_type=abstract
Astronomy and Astrophysics, v.357, p.1035-1044 (2000)
Astronomy and Astrophysics
Astrophysics
15
Stars: Circumstellar Matter, Stars: Individual: Fu Ori, Infrared: Ism: Lines And Bands, Infrared: Stars
Scientific paper
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 mu m) and the [CII] (158 mu m) 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 mu m), 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. ISO is an ESA project with instruments funded by ESA Member States and with the participation of ISAS and NASA
Benedettini Milena
Blake Geoffrey A.
Cohen Martin
Creech-Eakman Michelle
Giannini Teresa
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