The Water Vapor Abundance in Orion KL Outflows

We present the detection and modeling of more than 70 far-IR pure rotational lines of water vapor, including the 18O and 17O isotopologues, towards Orion KL. Observations were performed with the Long Wavelength Spectrometer Fabry-Perot (LWS/FP; R~6800-9700) on board the Infrared Space Observatory (ISO) between ~43 and ~197 um. The water line profiles evolve from P-Cygni type profiles (even for the H2O18 lines) to pure emission at wavelengths above ~100 um. We find that most of the water emission/absorption arises from an extended flow of gas expanding at 25+-5 kms^-1. Non-local radiative transfer models show that much of the water excitation and line profile formation is driven by the dust continuum emission. The derived beam averaged water abundance is 2-3x10^-5. The inferred gas temperature Tk=80-100 K suggests that: (i) water could have been formed in the "plateau" by gas phase neutral-neutral reactions with activation barriers if the gas was previously heated (e.g. by shocks) to >500 K and/or (ii) H2O formation in the outflow is dominated by in-situ evaporation of grain water-ice mantles and/or (iii) H2O was formed in the innermost and warmer regions (e.g. the hot core) and was swept up in ~1000 yr, the dynamical timescale of the outflow.Comment: Accepted for publication in ApJ letters [2006 August 7] (5 pages 2, figures, not edited

Far-IR Excited OH Lines from Orion KL Outflows

Accepted in ApJ letters, 2006 March 2As part of the first far-IR line survey towards Orion KL, we present the detection of seven new rotationally excited OH Lambda-doublets (at 48, 65, 71, 79, 98 and 115 um). Observations were performed with the Long Wavelength Spectrometer (LWS) Fabry-Perots on board the Infrared Space Observatory (ISO). In total, more than 20 resolved OH rotational lines, with upper energy levels up to 620 K, have been detected at an angular and velocity resolutions of 80$'' and 33 km s^-1 respectively. OH line profiles show a complex behavior evolving from pure absorption, P-Cygni type to pure emission. We also present a large scale 6' declination raster in the OH ^2\Pi_3/2 J=5/2^+-3/2^- and ^2\Pi_3/2 J=7/2^-5/2^+ lines (at 119.441 and 84.597 um) revealing the decrease of excitation outside the core of the cloud. From the observed profiles, mean intrinsic line widths and velocity offsets between emission and absorption line peaks we conclude that most of the excited OH arises from Orion outflow(s), i.e. the ``plateau'' component. We determine an averaged OH abundance relative to H_2 of X(OH)=(0.5-1.0)x10^-6, a kinetic temperature of 100 K and a density of n(H_2)=5x10^5 cm^-3. Even with these conditions, the OH excitation is heavily coupled with the strong dust continuum emission from the inner hot core regions and from the expanding flow itself.Peer reviewe

Physical parameters for Orion KL from modelling its ISO high-resolution far-IR CO line spectrum

International audienceAs part of the first high-resolution far-infrared (far-IR) spectral survey of the Orion Kleinmann-Low (KL) region, we observed 20 CO emission lines with Jup = 16 to 39 (upper levels from ~752 to 4294 K above the ground state). Observations were taken using the Long Wavelength Spectrometer on board the Infrared Space Observatory (ISO), in its high-resolution Fabry-Pérot (FP) mode (~33 km s-1). We present here an analysis of the final calibrated CO data, performed with a more sophisticated modelling technique than hitherto, including a detailed analysis of the chemistry, and discuss similarities and differences with previous results. The inclusion of chemical modelling implies that atomic and molecular abundances are time predicted by the chemistry. This provides one of the main differences with previous studies in which chemical abundances needed to be assumed as initial condition. The chemistry of the region is studied by simulating the conditions of the different known components of the KL region: chemical models for a hot core, a plateau and a ridge are coupled with an accelerated Lambda-iteration (ALI) radiative transfer model to predict line fluxes and profiles. We conclude that the CO transitions with 18 up 7 cm-3 rather from the plateau as previous studies had indicated. The rest of the transitions originate from shocked gas in a region of diameter ~0.06 pc with densities ranging from 3 × 105 to 1 × 106 cm-3. The resulting CO fractional abundances are in the range X(CO) = (7.0-4.7) × 10-5. A high-temperature post-shock region at more than 1000 K is necessary to reach transitions with Jup > 32, whilst transitions with Jup 2O and OH

Far-Infrared Excited Hydroxyl Lines from Orion KL Outflows

International audienceAs part of the first far-IR line survey toward Orion KL, we present the detection of seven new rotationally excited OH Lambda-doublets (at ~48, ~65, ~71, ~79, ~98, and ~115 mum). Observations were performed with the Long Wavelength Spectrometer Fabry-Pérot on board the Infrared Space Observatory. In total, more than 20 resolved OH rotational lines, with upper energy levels up to ~620 K, have been detected at angular and velocity resolutions of ~80" and ~33 km s-1, respectively. The OH line profiles show a complex behavior evolving from pure absorption, P Cygni type, to pure emission. We also present a large-scale, 6' declination raster in the OH 2Pi3/2 J=5/2+-3/2- and 2Pi3/2 J=7/2--5/2+ lines (at 119.441 and 84.597 mum) revealing a decrease of excitation outside the core of the cloud. From the observed profiles, mean intrinsic line widths, and velocity offsets between emission and absorption line peaks, we conclude that most of the excited OH arises from Orion outflow(s), that is, the ``plateau'' spectral component. We determine an averaged OH abundance relative to H2 of chi(OH)=(0.5-1.0)×10-6, a kinetic temperature of >~100 K, and a density of n(H2)~=5×105 cm-3. Even with these conditions, the OH excitation is heavily coupled with the strong dust continuum emission from the inner ``hot core'' regions and from the expanding flow itself

Far-Infrared Excited Hydroxyl Lines from Orion KL Outflows

International audienceAs part of the first far-IR line survey toward Orion KL, we present the detection of seven new rotationally excited OH Lambda-doublets (at ~48, ~65, ~71, ~79, ~98, and ~115 mum). Observations were performed with the Long Wavelength Spectrometer Fabry-Pérot on board the Infrared Space Observatory. In total, more than 20 resolved OH rotational lines, with upper energy levels up to ~620 K, have been detected at angular and velocity resolutions of ~80" and ~33 km s-1, respectively. The OH line profiles show a complex behavior evolving from pure absorption, P Cygni type, to pure emission. We also present a large-scale, 6' declination raster in the OH 2Pi3/2 J=5/2+-3/2- and 2Pi3/2 J=7/2--5/2+ lines (at 119.441 and 84.597 mum) revealing a decrease of excitation outside the core of the cloud. From the observed profiles, mean intrinsic line widths, and velocity offsets between emission and absorption line peaks, we conclude that most of the excited OH arises from Orion outflow(s), that is, the ``plateau'' spectral component. We determine an averaged OH abundance relative to H2 of chi(OH)=(0.5-1.0)×10-6, a kinetic temperature of >~100 K, and a density of n(H2)~=5×105 cm-3. Even with these conditions, the OH excitation is heavily coupled with the strong dust continuum emission from the inner ``hot core'' regions and from the expanding flow itself

A far-infrared molecular and atomic line survey of the Orion KL region

International audienceWe have carried out a high spectral resolution (lambda/Deltalambda ~ 6800-9700) line survey towards the Orion Kleinmann-Low (KL) cluster from 44 to 188 mum. The observations were taken with the Long Wavelength Spectrometer (LWS) in Fabry-Pérot mode, on board the Infrared Space Observatory (ISO). A total of 152 lines are clearly detected and a further 34 features are present as possible detections. The spectrum is dominated by the molecular species H2O, OH and CO, along with [OI] and [CII] lines from photodissociation region (PDR) or shocked gas and [O III] and [NIII] lines from the foreground M42 HII region. Several isotopic species, as well as NH3, are also detected. HDO and H3O+ are tentatively detected for the first time in the far-infrared (FIR) range towards Orion KL. A basic analysis of the line observations is carried out, by comparing with previous measurements and published models and deriving rotational temperatures and column densities in the case of the molecular species

A far-infrared molecular and atomic line survey of the Orion KL region

International audienceWe have carried out a high spectral resolution (lambda/Deltalambda ~ 6800-9700) line survey towards the Orion Kleinmann-Low (KL) cluster from 44 to 188 mum. The observations were taken with the Long Wavelength Spectrometer (LWS) in Fabry-Pérot mode, on board the Infrared Space Observatory (ISO). A total of 152 lines are clearly detected and a further 34 features are present as possible detections. The spectrum is dominated by the molecular species H2O, OH and CO, along with [OI] and [CII] lines from photodissociation region (PDR) or shocked gas and [O III] and [NIII] lines from the foreground M42 HII region. Several isotopic species, as well as NH3, are also detected. HDO and H3O+ are tentatively detected for the first time in the far-infrared (FIR) range towards Orion KL. A basic analysis of the line observations is carried out, by comparing with previous measurements and published models and deriving rotational temperatures and column densities in the case of the molecular species