Detection of Extended Hot Water in the Outflow from NGC 2071

We report the results of spectroscopic mapping observations carried out toward a ~1 min x 1 min region within the northern lobe of the outflow from NGC 2071 using the Infrared Spectrograph (IRS) of the Spitzer Space Telescope. These observations covered the 5.2-37 um spectral region and have led to the detection of a number of ionic, atomic, and molecular lines, including fine-structure emission of Si+, Fe+, S++, S, the S(0)-S(7) pure rotational lines of H2, the R(3) and R(4) transitions of HD, and at least 11 transitions of H2O. In addition, the 6.2, 7.4, 7.6, 7.9, 8.6 and 11.3 um PAH emission bands were also observed and several transitions of OH were tentatively detected. Most of the detected line transitions were strong enough to map including, for the first time, three transitions of hot H2O. We find that: (1) the water emission is extended; (2) the extended emission is aligned with the outflow; and, (3) the spatial distribution of the water emission generally follows that observed for H2. Based on the measured line intensities, we derive an HD abundance relative to H2 of 1.1-1.8 10^-5 and an H2O number density of 12-2 cm^3. The H2 density in the water-emitting region is not well constrained by our observations, but is likely between 3 10^4 and 10^6 cm^3, yielding an H2O abundance relative to H2 of between 2 10^-5 and 6 10^-4. Future observations planned for the Herschel Space Observatory should greatly improve the density estimate, and thus our knowledge of the H2O abundance, for the water-emitting regions reported here. Finally, we note a possible departure from the H2O ortho-to-para ratio of 3:1 expected for water formed in hot post-shocked gas, suggesting that a significant fraction of the water vapor we detect may arise from H2O sputtered from cold dust grains.Comment: 35 pages, 15 figures, 4 tables, accepted for publication in Ap

Distribution of Water Vapor in Molecular Clouds

We report the results of a large-area study of water vapor along the Orion Molecular Cloud ridge, the purpose of which was to determine the depth-dependent distribution of gas-phase water in dense molecular clouds. We find that the water vapor measured toward 77 spatial positions along the face-on Orion ridge, excluding positions surrounding the outflow associated with BN/KL and IRc2, display integrated intensities that correlate strongly with known cloud surface tracers such as CN, C2H, 13CO J =5-4, and HCN, and less well with the volume tracer N2H+. Moreover, at total column densities corresponding to Av < 15 mag., the ratio of H2O to C18O integrated intensities shows a clear rise approaching the cloud surface. We show that this behavior cannot be accounted for by either optical depth or excitation effects, but suggests that gas-phase water abundances fall at large Av. These results are important as they affect measures of the true water-vapor abundance in molecular clouds by highlighting the limitations of comparing measured water vapor column densities with such traditional cloud tracers as 13CO or C18O. These results also support cloud models that incorporate freeze-out of molecules as a critical component in determining the depth-dependent abundance of water vapor

GGD 37: An Extreme Protostellar Outflow

We present the first Spitzer-IRS spectral maps of the Herbig-Haro flow GGD 37 detected in lines of [Ne III], [O IV], [Ar III], and [Ne v]. The detection of extended [O IV] (55 eV) and some extended emission in [Ne v] (97 eV) indicates a shock temperature in excess of 100,000 K, in agreement with X-ray observations, and a shock speed in excess of 200 km s(-1). The presence of an extended photoionization or collisional ionization region indicates that GGD 37 is a highly unusual protostellar outflow.Jet Propulsion Laboratory, under NASA 1407NASA 1257184Jet Propulsion Laboratory (JPL) 960803University of Rochester 31419-5714Astronom

Precise Wavefront Correction with an Unbalanced Nulling Interferometer for Exo-Planet Imaging Coronagraphs

Very high dynamical range coronagraphs targeting direct exo-planet detection (10^9 - 10^10 contrast) at small angular separation (few lambda/D units) usually require an input wavefront quality on the order of ten thousandths of wavelength RMS. We propose a novel method based on a pre-optics setup that behaves partly as a low-efficiency coronagraph, and partly as a high-sensitivity wavefront aberration compensator (phase and amplitude). The combination of the two effects results in a highly accurate corrected wavefront. First, an (intensity-) unbalanced nulling interferometer (UNI) performs a rejection of part of the wavefront electric field. Then the recombined output wavefront has its input aberrations magnified. Because of the unbalanced recombination scheme, aberrations can be free of phase singular points (zeros) and can therefore be compensated by a downstream phase and amplitude correction (PAC) adaptive optics system, using two deformable mirrors. In the image plane, the central star's peak intensity and the noise level of its speckled halo are reduced by the UNI-PAC combination: the output-corrected wavefront aberrations can be interpreted as an improved compensation of the initial (eventually already corrected) incident wavefront aberrations. The important conclusion is that not all the elements in the optical setup using UNI-PAC need to reach the lambda/10000 rms surface error quality.Comment: Accepted for publication in A&

Submillimeter Wave Astronomy Satellite observations of comet 9P/Tempel 1 and Deep Impact

On 4 July 2005 at 5:52 UT the Deep Impact mission successfully completed its goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on the nucleus and ejecting material into the coma of the comet. NASA's Submillimeter Wave Astronomy Satellite (SWAS) observed the 1(10)-1(01) ortho-water ground-state rotational transition in comet 9P/Tempel 1 before, during, and after the impact. No excess emission from the impact was detected by SWAS and we derive an upper limit of 1.8e7 kg on the water ice evaporated by the impact. However, the water production rate of the comet showed large natural variations of more than a factor of three during the weeks before and after the impact. Episodes of increased activity with Q(H2O)~1e28 molecule/s alternated with periods with low outgassing (Q(H2O)<~5e27 molecule/s). We estimate that 9P/Tempel 1 vaporized a total of N~4.5e34 water molecules (~1.3e9 kg) during June-September 2005. Our observations indicate that only a small fraction of the nucleus of Tempel 1 appears to be covered with active areas. Water vapor is expected to emanate predominantly from topographic features periodically facing the Sun as the comet rotates. We calculate that appreciable asymmetries of these features could lead to a spin-down or spin-up of the nucleus at observable rates.Comment: 38 pages, 2 tables, 7 figures; Icarus, in pres

Herschel Search for O_2 toward the Orion Bar

We report the results of a search for molecular oxygen (O_2) toward the Orion Bar, a prominent photodissociation region at the southern edge of the H II region created by the luminous Trapezium stars. We observed the spectral region around the frequency of the O_2 NJ = 33-12 transition at 487 GHz and the 5_(4)-3_(4) transition at 774 GHz using the Heterodyne Instrument for the Far-Infrared on the Herschel Space Observatory. Neither line was detected, but the 3σ upper limits established here translate to a total line-of-sight O2 column density <1.5 × 10^(16) cm^(–2) for an emitting region whose temperature is between 30 K and 250 K, or <1 × 10^(16) cm^(–2) if the O_2 emitting region is primarily at a temperature of ≲100 K. Because the Orion Bar is oriented nearly edge-on relative to our line of sight, the observed column density is enhanced by a factor estimated to be between 4 and 20 relative to the face-on value. Our upper limits imply that the face-on O_2 column density is less than 4 × 10^(15) cm^(–2), a value that is below, and possibly well below, model predictions for gas with a density of 10^(4)-10^(5) cm^(–3) exposed to a far-ultraviolet flux 10^4 times the local value, conditions inferred from previous observations of the Orion Bar. The discrepancy might be resolved if (1) the adsorption energy of O atoms to ice is greater than 800 K; (2) the total face-on A V of the Bar is less than required for O_2 to reach peak abundance; (3) the O_2 emission arises within dense clumps with a small beam filling factor; or (4) the face-on depth into the Bar where O_2 reaches its peak abundance, which is density dependent, corresponds to a sky position different from that sampled by our Herschel beams

Water Abundance in Molecular Cloud Cores

We present Submillimeter Wave Astronomy Satellite (SWAS) observations of the 1_{10}-1_{01} transition of ortho-water at 557 GHz toward 12 molecular cloud cores. The water emission was detected in NGC 7538, Rho Oph A, NGC 2024, CRL 2591, W3, W3(OH), Mon R2, and W33, and was not detected in TMC-1, L134N, and B335. We also present a small map of the water emission in S140. Observations of the H_2^{18}O line were obtained toward S140 and NGC 7538, but no emission was detected. The abundance of ortho-water relative to H_2 in the giant molecular cloud cores was found to vary between 6x10^{-10} and 1x10^{-8}. Five of the cloud cores in our sample have previous water detections; however, in all cases the emission is thought to arise from hot cores with small angular extents. The water abundance estimated for the hot core gas is at least 100 times larger than in the gas probed by SWAS. The most stringent upper limit on the ortho-water abundance in dark clouds is provided in TMC-1, where the 3-sigma upper limit on the ortho-water fractional abundance is 7x10^{-8}.Comment: 5 pages, 3 Postscript figures, uses aastex.cls, emulateapj5.sty (included), and apjfonts.sty (included

The Distribution of Water Emission in M17SW

We present a 17-point map of the M17SW cloud core in the 1_{10}-1_{01} transition of ortho-water at 557 GHz obtained with the Submillimeter Wave Astronomy Satellite. Water emission was detected in 11 of the 17 observed positions. The line widths of the water emission vary between 4 and 9 km s^{-1}, and are similar to other emission lines that arise in the M17SW core. A direct comparison is made between the spatial extent of the water emission and the ^{13}CO J = 5\to4 emission; the good agreement suggests that the water emission arises in the same warm, dense gas as the ^{13}CO emission. A spectrum of the H_2^{18}O line was also obtained at the center position of the cloud core, but no emission was detected. We estimate that the average abundance of ortho-water relative to H_2 within the M17 dense core is approximately 1x10^{-9}, 30 times smaller than the average for the Orion core. Toward the H II region/molecular cloud interface in M17SW the ortho-water abundance may be about 5 times larger than in the dense core.Comment: 4 pages, 3 Postscript figures, uses aastex.cls, emulateapj5.sty (included), and apjfonts.sty (included

Spitzer spectral line mapping of protostellar outflows: I. Basic data and outflow energetics

We report the results of spectroscopic mapping observations carried out toward protostellar outflows in the BHR71, L1157, L1448, NGC 2071, and VLA 1623 molecular regions using the Infrared Spectrograph (IRS) of the Spitzer Space Telescope. These observations, covering the 5.2 - 37 micron spectral region, provide detailed maps of the 8 lowest pure rotational lines of molecular hydrogen and of the [SI] 25.25 micron and [FeII] 26.0 micron fine structure lines. The molecular hydrogen lines, believed to account for a large fraction of the radiative cooling from warm molecular gas that has been heated by a non-dissociative shock, allow the energetics of the outflows to be elucidated. Within the regions mapped towards these 5 outflow sources, total H2 luminosities ranging from 0.02 to 0.75 L(solar) were inferred for the sum of the 8 lowest pure rotational transitions. By contrast, the much weaker [FeII] 26.0 micron fine structure transition traces faster, dissociative shocks; here, only a small fraction of the fast shock luminosity emerges as line radiation that can be detected with Spitzer/IRS.Comment: 38 pages including 17 figures. Accepted for publication in Ap