Sofia/Exes Observations of Water Absorption in the Protostar Afgl 2591 at High Spectral Resolution

Indriolo, Nick; Neufeld, David A.; DeWitt, Curtis; Richter, Matthew J.; Boogert, A. C. A.; Harper, G. M.; Jaffe, D. T.; Kulas, Kristin R.; McKelvey, Mark E.; Ryde, Nils; Vacca, William D.

doi:10.1088/2041-8205/802/2/l14

Cited by 22 publications

(25 citation statements)

References 37 publications

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“…This number is consistent with the measured gaseous H 2 O column densities relative to those of hot H 2 in the inner region (Boonman & van Dishoeck 2003), with H 2 derived from CO infrared absorption lines obtained with the CFHT-FTS by Mitchell et al (1990) assuming CO/H 2 = 2 × 10 −4 . Interestingly, the corresponding ratio H 2 O/CO≈0.6 is similar to that found by Indriolo et al (2015a) for some of the same lines of sight using much higher spectral resolution H 2 O data obtained with SOFIA-EXES and VLT-CRIRES. Assuming that atomic O and O 2 are negligible, this gives a total of 162 ppm accounted for in the gas.…”

Section: G32 High-mass Protostarssupporting

confidence: 84%

“…Independent evidence that H 2 O does not contain all of the oxygen comes from mid-infrared absorption line observations with ISO and SOFIA of hot water and CO along the lines of sight to massive protostars, many of them the same sources as included in the WISH sample Boonman & van Dishoeck 2003). In particular, high spectral resolution absorption line observations at 6 µm using SOFIA-EXES give N(H 2 O)/N(CO) ≈ 0.7 for gas at ∼1000 K, a factor of 2-3 less than expected if all oxygen is in water (Indriolo et al 2015a).…”

Section: Outflow Positionsmentioning

confidence: 97%

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Water in star-forming regions: physics and chemistry from clouds to disks as probed by Herschel spectroscopy

Dishoeck

Kristensen²,

Mottram

et al. 2021

A&A

114

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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 > 105 L⊙) and from pre-stellar cores to protoplanetary disks. Lines of H2O 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 (> 105 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 Jup > 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 H2O/H2 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/H2O 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 NH3 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 102−103 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 μm-sized grains that do not contribute to infrared ice absorption. The fact that even warm outflows and hot cores do not show H2O 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 H2O line emission (Eup < 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.

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Section: G32 High-mass Protostarssupporting

confidence: 84%

Section: Outflow Positionsmentioning

confidence: 97%

Water in star-forming regions: physics and chemistry from clouds to disks as probed by Herschel spectroscopy

Dishoeck

Kristensen²,

Mottram

et al. 2021

A&A

114

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“…Our analysis is focused on the hot core AFGL 2591 VLA 3 whose kinematic and chemical properties have been studied at multiple wavelengths in the past. Based on the kinematic properties using PdBI observations of HDO, H 18 2 O, and SO 2 , Wang et al (2012) found a Hubble law-like expansion within the inner 2400 au, and argue that this is caused by a disk wind, (Indriolo et al 2015;Barr et al 2018). Jiménez-Serra et al (2012) reported chemical segregation on scales smaller than 3000 au due to the interplay between molecular dissociation by UV radiation, ice evaporation, and high-temperature gas-phase chemistry.…”

Section: Introductionmentioning

confidence: 99%

Chemical complexity in high-mass star formation

Gieser¹,

Semenov²,

Beuther³

et al. 2019

A&A

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Aims. In order to understand the observed molecular diversity in high-mass star-forming regions, we have to determine the underlying physical and chemical structure of those regions at high angular resolution and over a range of evolutionary stages. Methods. We present a detailed observational and modeling study of the hot core VLA 3 in the high-mass star-forming region AFGL 2591, which is a target region of the NOrthern Extended Millimeter Array (NOEMA) large program CORE. Using NOEMA observations at 1.37 mm with an angular resolution of ~0″. 42 (1400 au at 3.33 kpc), we derived the physical and chemical structure of the source. We modeled the observed molecular abundances with the chemical evolution code MUSCLE (MUlti Stage ChemicaL codE). Results. With the kinetic temperature tracers CH3CN and H2CO we observe a temperature distribution with a power-law index of q = 0.41 ± 0.08. Using the visibilities of the continuum emission we derive a density structure with a power-law index of p = 1.7 ± 0.1. The hot core spectra reveal high molecular abundances and a rich diversity in complex molecules. The majority of the molecules have an asymmetric spatial distribution around the forming protostar(s), which indicates a complex physical structure on scales <1400 au. Using MUSCLE, we are able to explain the observed molecular abundance of 10 out of 14 modeled species at an estimated hot core chemical age of ~21 100 yr. In contrast to the observational analysis, our chemical modeling predicts a lower density power-law index of p < 1.4. Reasons for this discrepancy are discussed. Conclusions. Combining high spatial resolution observations with detailed chemical modeling allows us to derive a concise picture of the physical and chemical structure of the famous AFGL 2591 hot core. The next steps are to conduct a similar analysis for the whole CORE sample, and then use this analysis to constrain the chemical diversity in high-mass star formation to a much greater depth.

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“…They detected CS in absorption, however only 6 lines were observed, as well as HNCO and CH 3 for the first time in the IR. Indriolo et al (2015) studied H 2 O absorption towards AFGL 2591 with the Echelon-Cross-Echelle Spectrograph (EXES; Richter et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Infrared Detection of Abundant CS in the Hot Core AFGL 2591 at High Spectral Resolution with SOFIA/EXES*

Barr

Boogert

DeWitt

et al. 2018

ApJL

Self Cite

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We have performed a 5-8 µm spectral line survey of the hot molecular core associated with the massive protostar AFGL 2591, using the Echelon-Cross-Echelle Spectrograph (EXES) on the Stratospheric Observatory for Infrared Astronomy (SOFIA). We have supplemented these data with a ground based study in the atmospheric M band around 4.5 µm using the iSHELL instrument on the Infrared Telescope Facility Corresponding author: Andrew G. Barr barr@strw.leidenuniv.nl * Observations made at the IRTF and SOFIA (IRTF), and the full N band window from 8-13 µm using the Texas Echelon Cross Echelle Spectrograph (TEXES) on the IRTF.Here we present the first detection of ro-vibrational transitions of CS in this source. The absorption lines are centred on average around -10 kms −1 and the line widths of CS compare well with the hot component of 13 CO (around 10 kms −1 ). Temperatures for CS, hot 13 CO and 12 CO v=1-2 agree well and are around 700 K. We derive a CS abundance of 8×10 −3 and 2×10 −6 with respect to CO and H 2 respectively. This enhanced CS abundance with respect to the surrounding cloud (1×10 −8 ) may reflect sublimation of H 2 S ice followed by gas-phase reactions to form CS.Transitions are in LTE and we derive a density of >10 7 cm −3 , which corresponds to an absorbing region of <0.04 ′′ . EXES observations of CS are likely to probe deeply into the hot core, to the base of the outflow. Submillimeter and infrared observations trace different components of the hot core as revealed by the difference in systemic velocities, line widths and temperatures, as well as the CS abundance.

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Sofia/Exes Observations of Water Absorption in the Protostar Afgl 2591 at High Spectral Resolution

Cited by 22 publications

References 37 publications

Water in star-forming regions: physics and chemistry from clouds to disks as probed by Herschel spectroscopy

Water in star-forming regions: physics and chemistry from clouds to disks as probed by Herschel spectroscopy

Chemical complexity in high-mass star formation

Infrared Detection of Abundant CS in the Hot Core AFGL 2591 at High Spectral Resolution with SOFIA/EXES*

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