Abundant gas-phase H<sub>2</sub>O in absorption toward massive protostars

Boonman, A. M. S.; Dishoeck, E. F. van

doi:10.1051/0004-6361:20030364

Cited by 55 publications

(49 citation statements)

References 30 publications

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“…Hot cores have long been known to show a rich chemistry with complex organic molecules. The same molecules we observe in emission in the T Tauri stars have also been detected in absorption in mid-infrared bands towards several hot cores using ISO (Lahuis & van Dishoeck 2000;Boonman & van Dishoeck 2003). The derived gas temperatures for the absorbing gas are in the same range as we found for the T Tauri stars.…”

Section: Comparison To Envelopes Outer Disks Comets and Hot Coressupporting

confidence: 82%

Organic Molecules and Water in the Inner Disks of T Tauri Stars

Carr

Najita

2011

ApJ

129

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We report high signal-to-noise Spitzer IRS spectra of a sample of eleven classical T Tauri stars. Molecular emission from rotational transitions of H 2 O and OH and ro-vibrational bands of simple organic molecules (CO 2 , HCN, C 2 H 2 ) is common among the sources in the sample. The emission shows a range in both flux and line-to-continuum ratio for each molecule and in the flux ratios of different molecular species. The gas temperatures (200-800 K) and emitting areas we derive are consistent with the emission originating in a warm disk atmosphere in the inner planet formation region at radii < 2 AU. The H 2 O emission appears to form under a limited range of excitation conditions, as demonstrated by the similarity in relative strengths of H 2 O features from star to star and the narrow range in derived temperature and column density.Emission from highly excited rotational levels of OH is present in all stars; the OH emission flux increases with the stellar accretion rate, and the OH/H 2 O flux ratio shows a relatively small scatter. We interpret these results as evidence for OH production via FUV photo-dissociation of H 2 O in the disk surface layers. No obvious explanation is found for the observed range in the relative emission strengths of different organic molecules or in their strength with respect to water. We put forward the possibility that these variations reflect a diversity in organic abundances due to star-to-star differences in the C/O ratio of the inner disk gas. Stars with the largest HCN/H 2 O flux ratios in our sample have the largest disk masses. While larger samples are required to confirm this, we speculate that such a trend could result if higher mass disks are more efficient at planetesimal formation and sequestration of water in the outer disk, leading to enhanced C/O ratios and abundances of organic molecules in the inner disk. A comparison of our derived HCN to H 2 O column density ratio to comets, hot cores, and outer T Tauri star disks suggests that the inner disks are chemically active.

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Section: Comparison To Envelopes Outer Disks Comets and Hot Coressupporting

confidence: 82%

Organic Molecules and Water in the Inner Disks of T Tauri Stars

Carr

Najita

2011

ApJ

129

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“…13) shows almost no lines of gas-phase molecules in contrast to the spectra toward the intermediate-mass protostar LkHα225 (van den Ancker 2000) and massive protostars Boonman et al 2000). For example, the ν 2 ro-vibrational band of gas-phase H 2 O at 6 µm, which is strong toward most of the massive protostars (Boonman et al 2000) has not been detected toward AFGL 490, placing an upper limit on the total amount of gas-phase H 2 O present (Table 8). Since gas-phase H 2 O abundances are predicted to be enhanced in warm regions and shocks, this indicates that AFGL 490 is not a "hot" source throughout the envelope.…”

Section: Results From Iso-swsmentioning

confidence: 99%

The young intermediate-mass stellar object AFGL 490 – A disk surrounded by a cold envelope

Schreyer¹,

Henning

Tak

et al. 2002

A&A

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Abstract. AFGL 490 is a key target of the class of deeply embedded intermediate-mass young stellar objects in a transition stage to Herbig Be stars (L = 2.2-4.0 × 10 3 L ). In this paper, we present a comprehensive set of single-dish line data which characterize the envelope of the source. In addition, observations of CS J = 2→1 and the corresponding continuum at 97.98 GHz have been obtained with the Plateau de Bure (PdB) interferometer, which are sensitive to the small-scale structure around the stellar source. The PdB line data show a bar-like elongated gas structure of 22 000 AU × 6000 AU size with a position angle of ≈-45• . This bar represents the flattened inner envelope surrounding a disk-like structure (radius ≤500 AU) for which we find evidence very close to the young B star. Due to strong (self-)absorption in the velocity range v lsr = -12.5 ... -15 km s −1 , only the outer line wings can be used to study the gas motion. Maps of the integrated red and blue line wing emission show two well-separated gas blobs around AFGL 490, which are interpreted as a disk. The 3 mm continuum interferometer map shows a point source at the position of AFGL 490 with a flux of 240 mJy. This flux translates into a total mass of 3-6 M of the disk which is comparable to the stellar mass of about 8 M . This configuration is unstable and will disappear in 10 3 -10 4 years due to gravitational instabilities. Photometric data from ISOPHOT and spectroscopic data from ISO-SWS have been obtained. Together with submillimetre continuum data a very complete spectral energy distribution of the envelope could be compiled. Analysis of the data shows that the central region of AFGL 490 has a steeper density gradient compared with the outer molecular envelope. All data clearly point to a low temperature (25-35 K) of this envelope. To determine the chemical state of the object, we determined the abundances of 13 molecules towards AFGL 490. The molecular line and ISO-SWS data are used to derive the gas-solid abundance ratios for H 2 O, CO, and CO 2 . The chemical results, such as the relatively low gas-to-solid ratios and the low CH 3 OH excitation, emphasize the presence of a cold molecular envelope. We found evidence for other outflow systems in the envelope around AFGL 490. Red-shifted and blue-shifted gas blobs with a separation of about 20 000 AU were detected. Their centre is located roughly 3 to the south of AFGL 490, and their morphology implies that a deeply embedded low-mass object drives a jet which enters the denser envelope material at such a large distance. Two further outflow systems in the close neighbourhood of AFGL 490 could be identified. All these data point to the formation of a group of low-mass stars around AFGL 490. It is very remarkable that these outflows do not influence the global physical and chemical structure of the envelope.

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“…For a dark cloud with a mean life time of 1 Myr, the total photodesorbed water would be 3.8 × 10 14 molecules cm −2 ∼ 0.4 ML. This is a low number compared to gasphase water abundance toward massive protostars ∼ 10 18 molecules cm −2 (Boonman et al 2000 andvan Dishoeck 2003) but in cold clouds, Zmuidzinas et al (1995) and Tauber et al (1996) have found that the gas-phase H 2 O abundance is low, ∼ 10 −8 to 10 −7 related to H 2 . Yeghikyan (2017), using the Cloudy code (Ferland et al 2013), calculated the effect of the irradiation on the abun-dance of water (ice and gas) in planetary nebulae (PN) for 1000 yr.…”

Section: Discussionmentioning

confidence: 96%

New measurements on water ice photodesorption and product formation under ultraviolet irradiation

Cruz-Díaz

Martín-Doménech

Moreno

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The photodesorption of icy grain mantles has been claimed to be responsible for the abundance of gas-phase molecules toward cold regions. Being water a ubiquitous molecule, it is crucial to understand its role in photochemistry and its behavior under an ultraviolet field. We report new measurements on the UV-photodesorption of water ice and its H 2 , OH, and O 2 photoproducts using a calibrated quadrupole mass spectrometer. Solid water was deposited under ultra-high-vacuum conditions and then UV-irradiated at various temperatures starting from 8 K with a microwave discharged hydrogen lamp. Deuterated water was used for confirmation of the results. We found a photodesorption yield of 1.3 × 10 −3 molecules per incident photon for water, and 0.7 × 10 −3 molecules per incident photon for deuterated water at the lowest irradiation temperature, 8 K. The photodesorption yield per absorbed photon is given and comparison with astrophysical scenarios, where water ice photodesorption could account for the presence of gas-phase water toward cold regions in the absence of a thermal desorption process is addressed.

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Abundant gas-phase H₂O in absorption toward massive protostars

Cited by 55 publications

References 30 publications

Organic Molecules and Water in the Inner Disks of T Tauri Stars

Organic Molecules and Water in the Inner Disks of T Tauri Stars

The young intermediate-mass stellar object AFGL 490 – A disk surrounded by a cold envelope

New measurements on water ice photodesorption and product formation under ultraviolet irradiation

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Abundant gas-phase H2O in absorption toward massive protostars

Cited by 55 publications

References 30 publications

Organic Molecules and Water in the Inner Disks of T Tauri Stars

Organic Molecules and Water in the Inner Disks of T Tauri Stars

The young intermediate-mass stellar object AFGL 490 – A disk surrounded by a cold envelope

New measurements on water ice photodesorption and product formation under ultraviolet irradiation

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Product

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Abundant gas-phase H₂O in absorption toward massive protostars