We present the first ~7.5'×11.5' velocity-resolved (~0.2 km s
) map of the C ii 158
m line toward the Orion molecular cloud 1 (OMC 1) taken with the
/HIFI instrument. In combination with far-infrared ...(FIR) photometric images and velocity-resolved maps of the H41
hydrogen recombination and CO
=2-1 lines, this data set provides an unprecedented view of the intricate small-scale kinematics of the ionized/PDR/molecular gas interfaces and of the radiative feedback from massive stars. The main contribution to the C ii luminosity (~85 %) is from the extended, FUV-illuminated face of the cloud (
>500,
>5×10
cm
) and from dense PDRs (
≳10
,
≳10
cm
) at the interface between OMC 1 and the H ii region surrounding the Trapezium cluster. Around ~15 % of the C ii emission arises from a different gas component without CO counterpart. The C ii excitation, PDR gas turbulence, line opacity (from
C ii) and role of the geometry of the illuminating stars with respect to the cloud are investigated. We construct maps of the
C ii/
and
/
ratios and show that
C ii/
decreases from the extended cloud component (~10
-10
) to the more opaque star-forming cores (~10
-10
). The lowest values are reminiscent of the "C ii deficit" seen in local ultra-luminous IR galaxies hosting vigorous star formation. Spatial correlation analysis shows that the decreasing
C ii/
ratio correlates better with the column density of dust through the molecular cloud than with
/
. We conclude that the C ii emitting column relative to the total dust column along each line of sight is responsible for the observed
C ii/
variations through the cloud.
Water In Star-forming regions with Herschel (WISH) is a key program on the Herschel Space Observatory designed to probe the physical and chemical structures of young stellar objects using water and ...related molecules and to follow the water abundance from collapsing clouds to planet-forming disks. About 80 sources are targeted, covering a wide range of luminosities-from low (< 1) to high (>10)-and a wide range of evolutionary stages-from cold prestellar cores to warm protostellar envelopes and outflows to disks around young stars. Both the HIFI and PACS instruments are used to observe a variety of lines of HO , HO and chemically related species at the source position and in small maps around the protostars and selected outflow positions. In addition, high-frequency lines of CO, CO , and CO are obtained with Herschel and are complemented by ground-based observations of dust continuum, HDO, CO and its isotopologs, and other molecules to ensure a self-consistent data set for analysis. An overview of the scientific motivation and observational strategy of the program is given, together with the modeling approach and analysis tools that have been developed. Initial science results are presented. These include a lack of water in cold gas at abundances that are lower than most predictions, strong water emission from shocks in protostellar environments, the importance of UV radiation in heating the gas along outflow walls across the full range of luminosities, and surprisingly widespread detection of the chemically related hydrides OH and HO in outflows and foreground gas. Quantitative estimates of the energy budget indicate that HO is generally not the dominant coolant in the warm dense gas associated with protostars. Very deep limits on the cold gaseous water reservoir in the outer regions of protoplanetary disks are obtained that have profound implications for our understanding of grain growth and mixing in disks.
Abstract We present JWST MIRI MRS observations of the edge-on protoplanetary disk around the young subsolar-mass star Tau 042021, acquired as part of the Cycle 1 GO program “Mapping Inclined Disk ...Astrochemical Signatures.” These data resolve the mid-IR spatial distributions of H 2 , revealing X-shaped emission extending to ∼200 au above the disk midplane with a semiopening angle of 35° ± 5°. We do not velocity-resolve the gas in the spectral images, but the measured semiopening angle of the H 2 is consistent with a magnetohydrodynamic wind origin. A collimated, bipolar jet is seen in forbidden emission lines from Ne ii , Ne iii , Ni ii , Fe ii , Ar ii , and S iii . Extended H 2 O and CO emission lines are also detected, reaching diameters of ∼90 and 190 au, respectively. Hot molecular emission is not expected at such radii, and we interpret its extended spatial distribution as scattering of inner disk molecular emission by dust grains in the outer disk surface. H i recombination lines, characteristic of inner disk accretion shocks, are similarly extended and are likely also scattered light from the innermost star–disk interface. Finally, we detect extended polycyclic aromatic hydrocarbon (PAH) emission at 11.3 μ m cospatial with the scattered-light continuum, making this the first low-mass T Tauri star around which extended PAHs have been confirmed, to our knowledge. MIRI MRS line images of edge-on disks provide an unprecedented window into the outflow, accretion, and scattering processes within protoplanetary disks, allowing us to constrain the disk lifetimes and accretion and mass-loss mechanisms.
Context.
Water is a key molecule in the physics and chemistry of star and planet formation, but it is difficult to observe from Earth. The
Herschel
Space Observatory provided unprecedented ...sensitivity as well as spatial and spectral resolution to study water. The Water In Star-forming regions with
Herschel
(WISH) key program was designed to observe water in a wide range of environments and provide a legacy data set to address its physics and chemistry.
Aims.
The aim of WISH is to determine which physical components are traced by the gas-phase water lines observed with
Herschel
and to quantify the excitation conditions and water abundances in each of these components. This then provides insight into how and where the bulk of the water is formed in space and how it is transported from clouds to disks, and ultimately comets and planets.
Methods.
Data and results from WISH are summarized together with those from related open time programs. WISH targeted ~80 sources along the two axes of luminosity and evolutionary stage: from low- to high-mass protostars (luminosities from <1 to > 10
5
L
⊙
) and from pre-stellar cores to protoplanetary disks. Lines of H
2
O and its isotopologs, HDO, OH, CO, and O I, were observed with the HIFI and PACS instruments, complemented by other chemically-related molecules that are probes of ultraviolet, X-ray, or grain chemistry. The analysis consists of coupling the physical structure of the sources with simple chemical networks and using non-LTE radiative transfer calculations to directly compare models and observations.
Results.
Most of the far-infrared water emission observed with
Herschel
in star-forming regions originates from warm outflowing and shocked gas at a high density and temperature (> 10
5
cm
−3
, 300–1000 K,
v
~ 25 km s
−1
), heated by kinetic energy dissipation. This gas is not probed by single-dish low-
J
CO lines, but only by CO lines with
J
up
> 14. The emission is compact, with at least two different types of velocity components seen. Water is a significant, but not dominant, coolant of warm gas in the earliest protostellar stages. The warm gas water abundance is universally low: orders of magnitude below the H
2
O/H
2
abundance of 4 × 10
−4
expected if all volatile oxygen is locked in water. In cold pre-stellar cores and outer protostellar envelopes, the water abundance structure is uniquely probed on scales much smaller than the beam through velocity-resolved line profiles. The inferred gaseous water abundance decreases with depth into the cloud with an enhanced layer at the edge due to photodesorption of water ice. All of these conclusions hold irrespective of protostellar luminosity. For low-mass protostars, a constant gaseous HDO/H
2
O ratio of ~0.025 with position into the cold envelope is found. This value is representative of the outermost photodesorbed ice layers and cold gas-phase chemistry, and much higher than that of bulk ice. In contrast, the gas-phase NH
3
abundance stays constant as a function of position in low-mass pre- and protostellar cores. Water abundances in the inner hot cores are high, but with variations from 5 × 10
−6
to a few × 10
−4
for low- and high-mass sources. Water vapor emission from both young and mature disks is weak.
Conclusions.
The main chemical pathways of water at each of the star-formation stages have been identified and quantified. Low warm water abundances can be explained with shock models that include UV radiation to dissociate water and modify the shock structure. UV fields up to 10
2
−10
3
times the general interstellar radiation field are inferred in the outflow cavity walls on scales of the
Herschel
beam from various hydrides. Both high temperature chemistry and ice sputtering contribute to the gaseous water abundance at low velocities, with only gas-phase (re-)formation producing water at high velocities. Combined analyses of water gas and ice show that up to 50% of the oxygen budget may be missing. In cold clouds, an elegant solution is that this apparently missing oxygen is locked up in larger
μ
m-sized grains that do not contribute to infrared ice absorption. The fact that even warm outflows and hot cores do not show H
2
O at full oxygen abundance points to an unidentified refractory component, which is also found in diffuse clouds. The weak water vapor emission from disks indicates that water ice is locked up in larger pebbles early on in the embedded Class I stage and that these pebbles have settled and drifted inward by the Class II stage. Water is transported from clouds to disks mostly as ice, with no evidence for strong accretion shocks. Even at abundances that are somewhat lower than expected, many oceans of water are likely present in planet-forming regions. Based on the lessons for galactic protostars, the low-
J
H
2
O line emission (
E
up
< 300 K) observed in extragalactic sources is inferred to be predominantly collisionally excited and to originate mostly from compact regions of current star formation activity. Recommendations for future mid- to far-infrared missions are made.
Ices are the main carriers of volatiles in protoplanetary disks and are crucial to our understanding of the protoplanetary disk chemistry that ultimately sets the organic composition of planets. The ...Director’s Discretionary-Early Release Science (DD-ERS) program Ice Age on the
James Webb
Space Telescope (JWST) follows the ice evolution through all stages of star and planet formation. JWST’s exquisite sensitivity and angular resolution uniquely enable detailed and spatially resolved inventories of ices in protoplanetary disks. JWST/NIRSpec observations of the edge-on Class II protoplanetary disk HH 48 NE reveal spatially resolved absorption features of the major ice components H
2
O, CO
2
, and CO, and multiple weaker signatures from less abundant ices NH
3
, OCN
−
, and OCS. Isotopologue
13
CO
2
ice has been detected for the first time in a protoplanetary disk. Since multiple complex light paths contribute to the observed flux, the ice absorption features are filled in by ice-free scattered light. This implies that observed optical depths should be interpreted as lower limits to the total ice column in the disk and that abundance ratios cannot be determined directly from the spectrum. The
12
CO
2
/
13
CO
2
integrated absorption ratio of 14 implies that the
12
CO
2
feature is saturated, without the flux approaching zero, indicative of a very high CO
2
column density on the line of sight, and a corresponding abundance with respect to hydrogen that is higher than interstellar medium values by a factor of at least a few. Observations of rare isotopologues are crucial, as we show that the
13
CO
2
observation allowed us to determine the column density of CO
2
to be at least 1.6 × 10
18
cm
−2
, which is more than an order of magnitude higher than the lower limit directly inferred from the observed optical depth. Spatial variations in the depth of the strong ice features are smaller than a factor of two. Radial variations in ice abundance, for example snowlines, are significantly modified since all observed photons have passed through the full radial extent of the disk. CO ice is observed at perplexing heights in the disk, extending to the top of the CO-emitting gas layer. Although poorly understood radiative transfer effects could contribute to this, we argue that the most likely interpretation is that we observed some CO ice at high temperatures, trapped in less volatile ices such as H
2
O and CO
2
. Future radiative transfer models will be required to constrain the physical origin of the ice absorption and the implications of these observations for our current understanding of disk physics and chemistry.
Context. Protostars interact with their surroundings through jets and winds impinging on the envelope and creating shocks, but the nature of these shocks is still poorly understood. Aims. Our aim is ...to survey far-infrared molecular line emission from a uniform and significant sample of deeply-embedded low-mass young stellar objects (YSOs) in order to characterize shocks and the possible role of ultraviolet radiation in the immediate protostellar environment. Methods. Herschel/PACS spectral maps of 22 objects in the Perseus molecular cloud were obtained as part of the William Herschel Line Legacy (WILL) survey. Line emission from H2O, CO, and OH is tested against shock models from the literature. Results. Observed line ratios are remarkably similar and do not show variations with physical parameters of the sources (luminosity, envelope mass). Most ratios are also comparable to those found at off-source outflow positions. Observations show good agreement with the shock models when line ratios of the same species are compared. Ratios of various H2O lines provide a particularly good diagnostic of pre-shock gas densities, nH ~ 105 cm-3, in agreement with typical densities obtained from observations of the post-shock gas when a compression factor on the order of 10 is applied (for non-dissociative shocks). The corresponding shock velocities, obtained from comparison with CO line ratios, are above 20 km s-1. However, the observations consistently show H2O-to-CO and H2O-to-OH line ratios that are one to two orders of magnitude lower than predicted by the existing shock models. Conclusions. The overestimated model H2O fluxes are most likely caused by an overabundance of H2O in the models since the excitation is well-reproduced. Illumination of the shocked material by ultraviolet photons produced either in the star-disk system or, more locally, in the shock, would decrease the H2O abundances and reconcile the models with observations. Detections of hot H2O and strong OH lines support this scenario.
We present new observations with the Infrared Spectrograph on board the Spitzer Space Telescope of the solid-CO sub(2) absorption feature near 15 km in the spectra of eight field stars behind the ...Taurus complex of dark clouds. Solid CO sub(2) is detected in six lines of sight. New results are combined with previous data to investigate the correlation of CO sub(2) column density with those of other major ice constituents (H sub(2)O and CO) and with extinction. CO sub(2) is shown to display a "threshold extinction" effect, i.e., a minimum extinction (A sub(0) = 4.3 c 1.0 mag) required for detection, behavior similar to that previously reported for H sub(2)O and CO. We find a particularly tight correlation through the origin between N(CO sub(2)) and N(H sub(2)O), confirming that these species form in tandem and coexist in the same (polar) ice layer on the grains. The observed composition of the mantles is broadly consistent with the predictions of photochemical models with diffusive surface chemistry proposed by Ruffle & Herbst. Comparison of our results for Taurus with published data for Serpens indicates significant differences in ice composition consistent with enhanced CO sub(2) production in the latter cloud. Our results also place constraints on the distribution of elemental oxygen between ices and other potential reservoirs. Assuming a constant N(H) to extinction ratio, we show that 665% of the solar O abundance is accounted for by summing the contributions of ices (626%), refractory dust (630%) and gas-phase CO (69%). If the Sun is an appropriate standard for the interstellar medium, the "missing" oxygen may reside in atomic O I gas and/or (undetected) O sub(2) within the ices.
'Water in Star-forming regions with Herschel' (WISH) is a Herschel Key Programme aimed at understanding the physical and chemical structure of young stellar objects (YSOs) with a focus on water and ...related species. The low-mass protostar HH 46 was observed with the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory to measure emission in H2O, CO, OH, OI, and CII lines located between 63 and 186 um. The excitation and spatial distribution of emission can disentangle the different heating mechanisms of YSOs, with better spatial resolution and sensitivity than previously possible. Far-IR line emission is detected at the position of the protostar and along the outflow axis. The OH emission is concentrated at the central position, CO emission is bright at the central position and along the outflow, and H2O emission is concentrated in the outflow. In addition, OI emission is seen in low-velocity gas, assumed to be related to the envelope, and is also seen shifted up to 170 km/s in both the red- and blue-shifted jets. Envelope models are constructed based on previous observational constraints. They indicate that passive heating of a spherical envelope by the protostellar luminosity cannot explain the high-excitation molecular gas detected with PACS, including CO lines with upper levels at >2500 K above the ground state. Instead, warm CO and H2O emission is probably produced in the walls of an outflow-carved cavity in the envelope, which are heated by UV photons and non-dissociative C-type shocks. The bright OH and OI emission is attributed to J-type shocks in dense gas close to the protostar. In the scenario described here, the combined cooling by far-IR lines within the central spatial pixel is estimated to be 2 \times 10-2 L_sun, with 60-80% attributed to J- and C-type shocks produced by interactions between the jet and the envelope.
![VELOCITY-RESOLVED [C ii] EM...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X_1538-4357/small "VELOCITY-RESOLVED [C ii] EMISSION AND [C ii]/FIR MAPPING ALONG ORION WITH HERSCHEL")
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