Water Line Emission Research Articles

Cold Water Emission Cannot Be Used to Infer Depletion of Bulk Elemental Oxygen [O/H] in Disks

We reexamine the constraints provided by Herschel Space Observatory data regarding cold water emission from protoplanetary disks. Previous disk models that were used to interpret observed water emission concluded that oxygen (O/H) is depleted by at least 2 orders of magnitude if a standard, interstellar gas/dust mass ratio is assumed in the disk. In this work, we use model results from a recent disk parameter survey and show that most of the Herschel constraints obtained for cold water (i.e., for transitions with an upper energy level E up < 200 K, where the bulk of the disk water lies) can be explained with disk models adopting interstellar medium-like oxygen elemental abundance (i.e., O/H = 3.2 × 10−4) and the canonical gas/dust mass ratio of 100. We show that cold water vapor is mainly formed by photodesorption of water ice at the interface between the molecular layer and the midplane, and that its emission is relatively independent of the main disk properties like the disk gas mass and gas/dust mass ratio. We find that the abundance of water vapor in the outer disk is set by photoprocesses and depends on the (constant) vertical column density of water ice needed to attenuate the far-ultraviolet photon flux, resulting in roughly constant emission for the parameters (gas mass, dust mass, disk radius) varied in our survey. Importantly, water line emission is found to be optically thick and hence sensitive to temperature more than abundance, possibly driving previous inferences of large-scale oxygen depletion.

ISLAT: the Interactive Spectral-line Analysis Tool for JWST and Beyond

We present the Interactive Spectral-Line Analysis Tool (iSLAT), a python-based graphical tool that allows users to interactively explore, inspect, and fit line emission observed in molecular spectra. iSLAT adopts a simple slab model in LTE that simulates emission spectra with a small set of parameters (temperature, emitting area, column density, and line broadening) that users can adjust in real time for multiple molecules or multiple thermal components of a same molecule. A central feature of iSLAT is the possibility to interactively inspect individual lines or line clusters to visualize their properties at high resolution and identify them in the population diagram. iSLAT provides a number of additional features, including the option to identify lines that are not blended at the instrumental resolution, the possibility to save custom line lists selected by the user, and to fit and measure their properties (line flux, width, and centroid) for later analysis. In this paper we launch the tool and demonstrate it on infrared spectra from the James Webb Space Telescope and ground-based instruments that provide higher resolving power. We also share curated line lists that are useful for the analysis of the forest of water emission lines observed from protoplanetary disks. iSLAT is shared with the community on GitHub.

High-contrast JWST-MIRI Spectroscopy of Planet-forming Disks for the JDISC Survey

The JWST Disk Infrared Spectral Chemistry Survey (JDISCS) aims to understand the evolution of the chemistry of inner protoplanetary disks using the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST). With a growing sample of >30 disks, the survey implements a custom method to calibrate the MIRI Medium Resolution Spectrometer (MRS) to contrasts of better than 1:300 across its 4.9–28 μm spectral range. This is achieved using observations of Themis family asteroids as precise empirical reference sources. The high spectral contrast enables precise retrievals of physical parameters, searches for rare molecular species and isotopologues, and constraints on the inventories of carbon- and nitrogen-bearing species. JDISCS also offers significant improvements to the MRS wavelength and resolving power calibration. We describe the JDISCS calibrated data and demonstrate their quality using observations of the disk around the solar-mass young star FZ Tau. The FZ Tau MIRI spectrum is dominated by strong emission from warm water vapor. We show that the water and CO line emission originates from the disk surface and traces a range of gas temperatures of ∼500–1500 K. We retrieve parameters for the observed CO and H2O lines and show that they are consistent with a radial distribution represented by two temperature components. A high water abundance of n(H2O) ∼ 10−4 fills the disk surface at least out to the 350 K isotherm at 1.5 au. We search the FZ Tau environs for extended emission, detecting a large (radius of ∼300 au) ring of emission from H2 gas surrounding FZ Tau, and discuss its origin.

The first ground-based detection of the 752 GHz water line in local ultra-luminous infrared galaxies using APEX-SEPIA

Abstract We report the first ground-based detection of the water line p-H2O (211–202) at 752.033 GHz in three z &amp;lt; 0.08 ultra-luminous infrared galaxies (ULIRGs): IRAS 06035-7102, IRAS 17207-0014 and IRAS 09022-3615. Using the Atacama Pathfinder EXperiment (APEX), with its Swedish-ESO PI Instrument for APEX (SEPIA) band-9 receiver, we detect this H2O line with overall signal-to-noise ratios of 8–10 in all three galaxies. Notably, this is the first detection of this line in IRAS 06035-7102. Our new APEX-measured fluxes, between 145 to 705 Jy km s−1, are compared with previous values taken from Herschel SPIRE FTS. We highlight the great capabilities of APEX for resolving the H2O line profiles with high spectral resolutions while also improving by a factor of two the significance of the detection within moderate integration times. While exploring the correlation between the p-H2O(211–202) and the total infrared luminosity, our galaxies are found to follow the trend at the bright end of the local ULIRG’s distribution. The p-H2O(211–202) line spectra are compared to the mid-J CO and HCN spectra, and dust continuum previously observed with ALMA. In the complex interacting system IRAS 09022-3615, the profile of the water emission line is offset in velocity with respect to the ALMA CO(J = 4 − 3) emission. For IRAS 17207-0014 and IRAS 06035-7102, the profiles between the water line and the CO lines are spectroscopically aligned. This pilot study demonstrates the feasibility of directly conducting ground-based high-frequency observations of this key water line, opening the possibility of detailed follow-up campaigns to tackle its nature.

The Way of Water: ALMA Resolves H2O Emission Lines in a Strongly Lensed Dusty Star-forming Galaxy at z ∼ 3.1

We report Atacama Large Millimeter/submillimeter Array (ALMA) high-resolution (≲0.3″) observations of water emission lines p-H2O(202 − 111), o-H2O(321 − 312), p-H2O(422 − 413), in the strongly lensed galaxy HATLASJ113526.2-01460 at redshift z ∼3.1. From the lensing-reconstructed maps of water emission and line profiles, we infer the general physical properties of the interstellar medium (ISM) in the molecular clouds where the lines arise. We find that the water vapor lines o-H2O(321 − 312), p-H2O(422 − 413) are mainly excited by far-infrared (FIR) pumping from dust radiation in a warm and dense environment, with dust temperatures ranging from 70 to ∼100 K, as suggested by the line ratios. The p-H2O(202 − 111) line, instead, is excited by a complex interplay between FIR pumping and collisional excitation in the dense core of the star-forming region. This scenario is also supported by the detection of the medium-level excitation of CO resulting in the line emission CO (J = 8–7). Thanks to the unprecedented high resolution offered by the combination of ALMA capabilities and gravitational lensing, we discern the different phases of the ISM and locate the hot molecular clouds into a physical scale of ∼500 pc. We discuss the possibility of J1135 hosting an active galactic nucleus in its accretion phase. Finally, we determine the relation between the water emission lines and the total IR luminosity of J1135, as well as the star formation rate as a function of water emission intensities, comparing the outcomes to local and high-z galactic samples from the literature.

Development of a Molecular Assessment High-Resolution Observation Spectrometer (MAHOS) for Microsatellites

Compact and lightweight sensors with a high-frequency resolution are required for the passive observation of atmospheric water and oxygen emission lines at a reduced cost and power consumption. A molecular assessment high-resolution observation spectrometer (MAHOS) is developed as a compact, low power, digital fast Fourier transform spectrometer to be installed on a microsatellite. MAHOS has a compact design with dimensions of <inline-formula> <tex-math notation="LaTeX">$0.154\times 0.125\times0.040$ </tex-math></inline-formula> m³ and mass of 0.7 kg. It uses only a few materials including a field-programmable gate array (FPGA) module with a lightweight aluminum alloy box. The highly stable spectrometer exhibits a sampling speed of 2.6624 GS/s and 16 384 frequency channels. The stability of the spectrometer is longer than 1200 s within the 1-GHz bandwidth. Thermal dissipation is achieved through a heat conductive gel filled in the gap between the most heat-generating component, the FPGA, and the aluminum alloy case. Results of a finite element analysis indicate that the design is stiff and stable enough to survive in the launch environment. Thermal analysis indicates the durability of the system during operation. Even in space where heat dissipation is not possible, self-heating temperatures are not a problem for the FPGA. In the future, the performance of the spectrometer will be verified by conducting environmental tests.

Smoke on the water: CO and H2O in a circumnuclear disc around a quasar at redshift 2.64

ABSTRACT We present an analysis of observations with the Atacama Large (sub-)Millimetre Array (ALMA) of the 380 GHz water emission line and CO (11–10) emission line from MG J0414+0534, a gravitationally lensed dusty star-forming galaxy that hosts a type 1 quasar. We also present observations at 1.6 GHz with global very long baseline interferometry of the radio source. We confirm the previously reported detection of the 380 GHz water line and that the flux density ratio between the two merging lensed images is reversed with respect to the radio/mm continuum. We further find tentative evidence of variability in the integrated line intensity on time-scales of days. We show that the 380 GHz water line has two components of emission: a disc that is around 35 pc in diameter around the quasar, and another component of emission that is offset ∼600 pc perpendicular to the disc that lies close to the lensing caustic. With lens modelling of the multiwavelength data sets, we construct a model for the quasar system consisting of a circumnuclear disc of molecular gas with a size of about 60 pc bisected by radio jets extending to a distance of about 200 pc from the radio core. Our findings suggest that observations with ALMA of high-excitation molecular lines from strongly lensed quasars could allow detailed studies of active galactic nucleus accretion and feedback at the cosmic peak of black hole and galaxy growth.

The water line emission and ortho-to-para ratio in the Orion Bar photon-dominated region

Context. The ortho-to-para ratio (OPR) of water in the interstellar medium (ISM) is often assumed to be related to the formation temperature of water molecules, making it a potentially interesting tracer of the thermal history of interstellar gas. Aims. A very low OPR of 0.1–0.5 was previously reported in the Orion Bar photon-dominated region (PDR), based on observations of two optically thin H218O lines which were analyzed by using a single-slab large velocity gradient (LVG) model. The corresponding spin temperature does not coincide with the kinetic temperature of the molecular gas in this UV-illuminated region. This was interpreted as an indication of water molecules being formed on cold icy grains which were subsequently released by UV photodesorption. Methods. A more complete set of water observations in the Orion Bar, including seven H216O lines and one H218O line, carried out using Herschel/HIFI instrument, was reanalyzed using the Meudon PDR code to derive gas-phase water abundance and the OPR. The model takes into account the steep density and temperature gradients present in the region. Results. The model line intensities are in good agreement with the observations assuming that water molecules formed with an OPR corresponding to thermal equilibrium conditions at the local kinetic temperature of the gas and when solely considering gas-phase chemistry and water gas-grain exchanges through adsorption and desorption. Gas-phase water is predicted to arise from a region deep into the cloud, corresponding to a visual extinction of AV ~ 9, with a H216O fractional abundance of ~2 × 10−7 and column density of (1.4 ± 0.8) × 1015 cm−2 for a total cloud depth of AV = 15. A line-of-sight average OPR of 2.8 ± 0.2 is derived. Conclusions. The observational data are consistent with a nuclear spin isomer repartition corresponding to the thermal equilibrium at a temperature of 36 ± 2 K, much higher than the spin temperature previously reported for this region and close to the gas kinetic temperature in the water-emitting gas.

A High-resolution Mid-infrared Survey of Water Emission from Protoplanetary Disks

Abstract We present the largest survey of spectrally resolved mid-infrared water emission to date, with spectra for 11 disks obtained with the Michelle and TEXES spectrographs on Gemini North. Water emission is detected in six of eight disks around classical T Tauri stars. Water emission is not detected in the transitional disks SR 24 N and SR 24 S, in spite of SR 24 S having pretransitional disk properties like DoAr 44, which does show water emission. With R ∼ 100,000, the TEXES water spectra have the highest spectral resolution possible at this time, and allow for detailed line shape analysis. We find that the mid-IR water emission lines are similar to the “narrow component” in CO rovibrational emission, consistent with disk radii of a few astronomical units. The emission lines are either single peaked, or consistent with a double peak. Single-peaked emission lines cannot be produced with a Keplerian disk model, and may suggest that water participates in the disk winds proposed to explain single-peaked CO emission lines. Double-peaked emission lines can be used to determine the radius at which the line emission luminosity drops off. For HL Tau, the lower limit on this measured dropoff radius is consistent with the 13 au dark ring. We also report variable line/continuum ratios from the disks around DR Tau and RW Aur, which we attribute to continuum changes and line flux changes, respectively. The reduction in RW Aur line flux corresponds with an observed dimming at visible wavelengths.

Infrared borescopic characterization of corona and conventional ignition for lean/dilute combustion in heavy-duty natural-gas engines

Natural gas (NG) is attractive for heavy-duty (HD) engines for reasons of cost stability, emissions, and fuel security. NG requires forced ignition, but conventional gasoline-engine ignition systems are not optimized for NG and are challenged to ignite mixtures that are lean or diluted with exhaust-gas recirculation (EGR). NG ignition is particularly difficult in large-bore engines, where it is more challenging to complete combustion in the time available. High-speed infrared (IR) in-cylinder imaging and image-derived quantitative metrics were used to compare two ignition systems in terms of the early flame-kernel development and cycle-to-cycle variability (CCV) in a heavy-duty, natural-gas-fueled engine that had been modified to enable exhaust-gas recirculation and to provide optical access via borescopes. Imaging in the near IR and short-wavelength IR yielded strong signals from the water emission lines, which acted as a proxy for flame front and burned-gas regions while obviating image intensification (which can reduce spatial resolution). The ignition systems studied were a conventional system and a high-frequency corona system. The air/fuel mixtures investigated included stoichiometric without dilution and lean with EGR. The corona system produced five separate elongated, irregularly shaped, nonequilibrium-plasma streamers, leading to immediate formation of five spatially distinct wrinkled flame kernels around each streamer. Compared to the conventional spark ignition, which produces a single flame kernel that exhibits an initial laminar growth regime before wrinkling, corona ignition's early achievement of higher flame surface areas significantly shortened the ignition delay, resulting in reduced overall combustion duration and CCV for each mixture. Additionally, although the lean, dilute mixture produced higher CCV than the stoichiometric, minimally diluted mixture with both igniters, the mixtures ignited by the corona system suffered less than those ignited by the conventional system. Image-based measurements of CCV agreed with those based on in-cylinder pressure.

The Volatile Composition of Comet C/2017 E4 (Lovejoy) before its Disruption, as Revealed by High-resolution Infrared Spectroscopy with iSHELL at the NASA/IRTF

Abstract In 2017 April, we acquired comprehensive high-resolution spectra of newly discovered comet C/2017 E4 (Lovejoy) as it approached perihelion, and before its disintegration. We detected many cometary emission lines in the range (2.8–5.3) μm, in four customized instrument settings (L1-c, L3, Lp1-c, and M1) of iSHELL—the new near-IR high-resolution immersion echelle spectrograph at NASA/IRTF (Maunakea, Hawaii). We identified 12 molecular species: nine primary volatiles (H2O, HCN, NH3, CO, C2H2, C2H6, CH4, CH3OH, H2CO) and three product species (CN, NH2, OH). We detected 85 H2O emission lines from 12 water vibrational bands across L1-c and M1 settings. The many detected water emission lines enabled retrieval of accurate measures for ortho- and para-H2O independently, thereby reducing systematic uncertainty in the derived ortho–para ratio and nuclear spin temperature. Excitation analyses and emission profile analyses were performed for all species, and molecular abundance ratios relative to water are compared with values found for other Oort Cloud comets in our infrared database. Abundance ratios are consistent for most species, with the exception of underabundant methanol and overabundant ammonia in E4.

Search for the 22 GHz water maser emission in selected comets

Following the first evidence of planetary water maser emission induced by the collision of comet Shoemaker/Levy with Jupiter and the puzzling detection of the 22GHz water emission line in Comet Hyakutake we started in the period 2002–2008 systematic observations of selected comets at 22GHz (1.35cm) with the aim of clarifying the unusual behavior of the maser line in the cometary “scenario”. Using a fast multichannel spectrometer coupled to the 32m dish of the Medicina (Bologna, Italy) Radio Telescope we investigated 6 bright or sungrazing comets down to a heliocentric distance of 0.11AU: 96P/Machholz, 153P/ Ikeya–Zhang, C/2002 V1 (NEAT), C/2002 X5 (Kudo–Fujikawa), C/2002 T7 (Linear), and 73P/Schwassmann–Wachmann 3. All of them, similarly to Comet Hyakutake, demonstrate spectral features that, if real and due to the 1.35cm water vapor transition, are strongly (up to tens of km/s) shifted relative to the radial velocity of the nucleus and, at least sometimes, seem to be present as two separate peaks. If our interpretation of these spectral peaks is correct, there must be some mechanism of acceleration of neutral water molecules up to the velocities of ions. We discuss here the results achieved and the possible explanation of the chemo-physical constraints.

Water in star-forming regions withHerschel(WISH)

To understand the origin of water line emission and absorption during high-mass star formation, we decompose high-resolution Herschel-HIFI line spectra toward 19 high-mass star-forming regions into three distinct physical components. Protostellar envelopes are usually seen as narrow absorptions or emissions in the H2O 1113 and 1669 GHz ground-state lines, the H2O 987 GHz excited-state line, and the H2O-18 1102 GHz ground-state line. Broader features due to outflows are usually seen in absorption in the H2O 1113 and 1669 GHz lines, in 987 GHz emission, and not seen in H2O-18, indicating a low column density and a high excitation temperature. The H2O 1113 and 1669 GHz spectra show narrow absorptions by foreground clouds along the line of sight, which have a low column density and a low excitation temperature, although their H2O ortho/para ratios are close to 3. The intensities of the H2O 1113 and 1669 GHz lines do not show significant trends with luminosity, mass, or age. In contrast, the 987 GHz line flux increases with luminosity and the H2O-18 line flux decreases with mass. Furthermore, appearance of the envelope in absorption in the 987 GHz and H2O-18 lines seems to be a sign of an early evolutionary stage. We conclude that the ground state transitions of H2O trace the outer parts of the envelopes, so that the effects of star formation are mostly noticeable in the outflow wings. These lines are heavily affected by absorption, so that line ratios of H2O involving the ground states must be treated with caution. The average H2O abundance in high-mass protostellar envelopes does not change much with time. The 987 GHz line appears to be a good tracer of the mean weighted dust temperature of the source, which may explain why it is readily seen in distant galaxies.

HERSCHEL/HIFI OBSERVATIONS OF A NEW INTERSTELLAR WATER MASER: THE 532-441TRANSITION AT 620.701 GHz

Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared (HIFI), we have performed mapping observations of the 620.701 GHz 5(32)-4(41) transition of ortho-H2O within a roughly 1.5 x 1.5 arcmin region encompassing the Kleinmann-Low nebula in Orion, and pointed observations of that transition toward the Orion South condensation and the W49N region of high-mass star formation. Using the Effelsberg 100 m radio telescope, we obtained ancillary observations of the 22.23508 GHz 6(16)-5(23) water maser transition; in the case of Orion-KL, the 621 GHz and 22 GHz observations were carried out within 10 days of each other. The 621 GHz water line emission shows clear evidence for strong maser amplication in all three sources, exhibiting narrow (roughly 1 km/s FWHM) emission features that are coincident (kinematically and/or spatially) with observed 22 GHz features. Moreover, in the case of W49N - for which observations were available at three epochs spanning a two year period - the spectra exhibited variability. The observed 621 GHz/22 GHz line ratios are consistent with a maser pumping model in which the population inversions arise from the combined effects of collisional excitation and spontaneous radiative decay, and the inferred physical conditions can plausibly arise in gas heated by either dissociative or non-dissociative shocks. The collisional excitation model also predicts that the 22 GHz population inversion will be quenched at higher densities than that of the 621 GHz transition, providing a natural explanation for the observational fact that 22 GHz maser emission appears to be a necessary but insufficient condition for 621 GHz maser emission.

H2O line mapping at high spatial and spectral resolution

Apart from being an important coolant, H2O is known to be a tracer of high-velocity molecular gas. Recent models predict relatively high abundances behind interstellar shockwaves. The dynamical and physical conditions of the H2O emitting gas, however, are not fully understood yet. We aim to determine the abundance and distribution of H2O, its kinematics and the physical conditions of the gas responsible for the H2O emission. The observed line profile shapes help us understand the dynamics in molecular outflows. We mapped the VLA1623 outflow, in the ground-state transitions of o-H2O, with the HIFI and PACS instruments. We also present observations of higher energy transitions of o-H2O and p-H2O obtained with HIFI and PACS towards selected outflow positions. From comparison with non-LTE radiative transfer calculations, we estimate the physical parameters of the water emitting regions. The observed water emission line profiles vary over the mapped area. Spectral features and components, tracing gas in different excitation conditions, allow us to constrain the density and temperature of the gas. The H2O emission originates in a region where temperatures are comparable to that of the warm H2 gas (T\gtrsim200K). Thus, the H2O emission traces a gas component significantly warmer than the gas responsible for the low-J CO emission. The H2O column densities at the CO peak positions are low, i.e. N(H2O) \simeq (0.03-10)x10e14 cm-2. The H2O abundance with respect to H2 in the extended outflow is estimated at X(H2O)<1x10e-6, significantly lower than what would be expected from most recent shock models. The H2O emission traces a gas component moving at relatively high velocity compared to the low-J CO emitting gas. However, other dynamical quantities such as the momentum rate, energy and mechanical luminosity are estimated to be the same, independent of the molecular tracer used, CO or H2O.

Water in Protoplanetary Disks

AbstractInfrared water line emission from protoplanetary disks, recently observed by the Spitzer and Herschel space telescopes, is thought to trace the surface layer of the inner to outer regions of the disks. We have modelled the water abundance profile and line emission, especially focusing on the effects of dust size growth and turbulent mixing. Comparison between model calculations and observations suggests a small grain model with turbulent mixing is preferred.

The formation heritage of Jupiter Family Comet 10P/Tempel 2 as revealed by infrared spectroscopy

We present spectral and spatial information for major volatile species in Comet 10P/Tempel 2, based on high-dispersion infrared spectra acquired on UT 2010 July 26 (heliocentric distance Rh=1.44AU) and September 18 (Rh=1.62AU), following the comet’s perihelion passage on UT 2010 July 04. The total production rate for water on July 26 was (1.90±0.12)×1028moleculess−1, and abundances of six trace gases (relative to water) were: CH3OH (1.58%±0.23%), C2H6 (0.39%±0.04%), NH3 (0.83%±0.20%), and HCN (0.13%±0.02%). A detailed analysis of intensities for water emission lines provided a rotational temperature of 35±3K. The mean OPR is consistent with nuclear spin populations in statistical equilibrium (OPR=3.01±0.18), and the (1σ) lower bound corresponds to a spin temperature >38K. Our measurements were contemporaneous with a jet-like feature observed at optical wavelengths. The spatial profiles of four primary volatiles display strong enhancements in the jet direction, which favors release from a localized vent on the nucleus. The measured IR continuum is much more sharply peaked and is consistent with a dominant contribution from the nucleus itself. The peak intensities for H2O, CH3OH, and C2H6 are offset by ∼200km in the jet direction, suggesting the possible existence of a distributed source, such as the release of icy grains that subsequently sublimed in the coma. On UT September 18, no obvious emission lines were present in our spectra, nevertheless we obtained a 3σ upper limit Q(H2O)<2.86×1027moleculess−1.

Water emission from the chemically rich outflow L1157

In the framework of the Herschel-WISH key program, several ortho-H2O and para-H2O emission lines, in the frequency range from 500 to 1700 GHz, were observed with the HIFI instrument in two bow-shock regions (B2 and R) of the L1157 cloud. The primary aim is to analyse water emission lines as a diagnostic of the physical conditions in the blue (B2) and red-shifted (R) lobes to compare the excitation conditions. A total of 5 ortho- and para-H216O plus one o-H218O transitions were observed in B2 and R with a wide range of excitation energies (27 K<=Eu<=215 K). The H2O spectra, observed in the two shocked regions, show that the H2O profiles are markedly different in the two regions. In particular, at the bow-shock R, we observed broad (~30 km s-1 with respect to the ambient velocity) red-shifted wings where lines at different excitation peak at different red-shifted velocities. The B2 spectra are associated with a narrower velocity range (~6 km s-1), peaking at the systemic velocity. The excitation analysis suggests, for B2, low values of column density NH2O <=5{\times}1013 cm-2, a density range of 105 <=nH2 <=107 cm-3, and warm temperatures (>=300 K). The presence of the broad red-shifted wings and multiple peaks in the spectra of the R region, prompted the modelling of two components. High velocities are associated with relatively low temperatures (~100K),NH2O{\simeq}5{\times}1012-5{\times}1013 cm-2 and densities nH2{\simeq}106-108 cm-3.Lower velocities are associated with higher excitation conditions with Tkin>=300 K, very dense gas (nH2 ~108 cm-3) and low column density (NH2O<5{\times}1013 cm-2).

WARM H2O AND OH DISK EMISSION IN V1331 Cyg

We present high resolution (R=24,000) L-band spectra of the young intermediate mass star V1331 Cyg obtained with NIRSPEC on the Keck II telescope. The spectra show strong, rich emission from water and OH that likely arises from the warm surface region of the circumstellar disk. We explore the use of the new BT2 (Barber et al. 2006) water line list in fitting the spectra, and we find that it does a much better job than the well-known HITRAN (Rothman et al. 1998) water line list in the observed wavelength range and for the warm temperatures probed by our data. By comparing the observed spectra with synthetic disk emission models, we find that the water and OH emission lines have similar widths (FWHM ~ 18 km s-1). If the line widths are set by disk rotation, the OH and water emission lines probe a similar range of disk radii in this source. The water and OH emission are consistent with thermal emission for both components at a temperature ~ 1500 K. The column densities of the emitting water and OH are large, ~ 10^{21} cm-2 and ~ 10^{20} cm-2, respectively. Such a high column density of water is more than adequate to shield the disk midplane from external UV irradiation in the event of complete dust settling out of the disk atmosphere, enabling chemical synthesis to continue in the midplane despite a harsh external UV environment. The large OH-to-water ratio is similar to expectations for UV irradiated disks (e.g., Bethell and Bergin 2009), although the large OH column density is less easily accounted for.

WATER DEPLETION IN THE DISK ATMOSPHERE OF HERBIG AeBe STARS

We present high resolution (R = 100,000) L-band spectroscopy of 11 Herbig AeBe stars with circumstellar disks. The observations were obtained with the VLT/CRIRES to detect hot water and hydroxyl radical emission lines previously detected in disks around T Tauri stars. OH emission lines are detected towards 4 disks. The OH P4.5 (1+,1-) doublet is spectrally resolved as well as the velocity profile of each component of the doublet. Its characteristic double-peak profile demonstrates that the gas is in Keplerian rotation and points to an emitting region extending out to ~ 15-30 AU. The OH, emission correlates with disk geometry as it is mostly detected towards flaring disks. None of the Herbig stars analyzed here show evidence of hot water vapor at a sensitivity similar to that of the OH lines. The non-detection of hot water vapor emission indicates that the atmosphere of disks around Herbig AeBe stars are depleted of water molecules. Assuming LTE and optically thin emission we derive a lower limit to the OH/H2O column density ratio > 1 - 25 in contrast to T Tauri disks for which the column density ratio is 0.3 -- 0.4.