An ALMA Survey of H<sub>2</sub>CO in Protoplanetary Disks

Pegues, Jamila; Öberg, Karin I.; Bergner, Jennifer B.; Loomis, Ryan A.; Qi, Chunhua; Gal, Romane Le; Cleeves, L. Ilsedore; Guzmán, Viviana V.; Huang, Jane; Jørgensen, J. K.; Andrews, Sean M.; Blake, Geoffrey A.; Carpenter, John M.; Schwarz, Kamber R.; Williams, Jonathan P.; Wilner, David J.

doi:10.3847/1538-4357/ab64d9

Cited by 68 publications

(114 citation statements)

References 81 publications

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“…The minimum and maximum column densities over this range of T ex are summarized in Table 1. The assumed T ex values are in agreement with those inferred from multi-line observations of CS and H 2 CO in a few Class II disks (e.g., Le Gal et al 2019;Pegues et al 2020), while no estimates of T ex in Class I disks are available. The total H 2 CO and CH 3 OH column densities were derived assuming an ortho-to-para ratio of 1.8−2.8 (Guzmán et al 2018) and the ratio of A-type to E-type forms to be one.…”

Section: Column Densities In the Midplane And Molecular Layersupporting

confidence: 78%

“…On the other hand, it is lower by a factor of ∼2.5 than that inferred for the Class II disk of TW Hya (∼1.27−1.73 for T ex ∼ 25−75 K, Walsh et al 2016;Carney et al 2019), while it is larger than the upper limit obtained for HD 163296 (<0.24, Carney et al 2019). As methanol forms on the dust grains due to CO freeze-out and subsequent hydrogenation, the lower [CH 3 OH]/[H 2 CO] in HD 163296 may be due to a smaller degree of CO ice chemistry in the warmer disks around Herbig stars (e.g., Pegues et al 2020). The abundance ratios in Class I and Class II disks are from a factor of 2 to 2 orders of magnitude lower than the values inferred in the hot corinos around the Class 0 protostars IRAS 16293-2422 A and B in Taurus (Jørgensen et al 2018;Persson et al 2018;Manigand et al 2020), and NGC 1333-IRAS 4A and IRAS 2A in Perseus (Taquet et al 2015).…”

Section: Discussionmentioning

confidence: 72%

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ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

Podio

Garufi

Codella

et al. 2020

A&A

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The chemical composition of planets is inherited from that of the natal protoplanetary disk at the time of planet formation. Increasing observational evidence suggests that planet formation occurs in less than 1−2 Myr. This motivates the need for spatially resolved spectral observations of young Class I disks, as carried out by the ALMA chemical survey of Disk-Outflow sources in Taurus (ALMA-DOT). In the context of ALMA-DOT, we observe the edge-on disk around the Class I source IRAS 04302+2247 (the butterfly star) in the 1.3 mm continuum and five molecular lines. We report the first tentative detection of methanol (CH3OH) in a Class I disk and resolve, for the first time, the vertical structure of a disk with multiple molecular tracers. The bulk of the emission in the CO 2−1, CS 5−4, and o–H2CO 31, 2 − 21, 1 lines originates from the warm molecular layer, with the line intensity peaking at increasing disk heights, z, for increasing radial distances, r. Molecular emission is vertically stratified, with CO observed at larger disk heights (aperture z/r ∼ 0.41−0.45) compared to both CS and H2CO, which are nearly cospatial (z/r ∼ 0.21−0.28). In the outer midplane, the line emission decreases due to molecular freeze-out onto dust grains (freeze-out layer) by a factor of > 100 (CO) and 15 (CS). The H2CO emission decreases by a factor of only about 2, which is possibly due to H2CO formation on icy grains, followed by a nonthermal release into the gas phase. The inferred [CH3OH]/[H2CO] abundance ratio is 0.5−0.6, which is 1−2 orders of magnitude lower than for Class 0 hot corinos, and a factor ∼2.5 lower than the only other value inferred for a protoplanetary disk (in TW Hya, 1.3−1.7). Additionally, it is at the lower edge but still consistent with the values in comets. This may indicate that some chemical reprocessing occurs in disks before the formation of planets and comets.

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Section: Column Densities In the Midplane And Molecular Layersupporting

confidence: 78%

Section: Discussionmentioning

confidence: 72%

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

Podio

Garufi

Codella

et al. 2020

A&A

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“…Mask outer radii are chosen to encompass the observed emission. A full description of the masking technique can be found in Bergner et al (2018) and Pegues et al (2020). Deprojected radial profiles were generated using the disk inclinations and position angles in Table 8.…”

Section: Spectral Extractionmentioning

confidence: 99%

An Evolutionary Study of Volatile Chemistry in Protoplanetary Disks

Bergner

Öberg

Bergin

et al. 2020

ApJ

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The volatile composition of a planet is determined by the inventory of gas and ice in the parent disk. The volatile chemistry in the disk is expected to evolve over time, though this evolution is poorly constrained observationally. We present ALMA observations of C 18 O, C 2 H, and the isotopologues H 13 CN, HC 15 N, and DCN towards five Class 0/I disk candidates. Combined with a sample of fourteen Class II disks presented in Bergner et al. (2019b), this data set offers a view of volatile chemical evolution over the disk lifetime. Our estimates of C 18 O abundances are consistent with a rapid depletion of CO in the first ∼0.5-1 Myr of the disk lifetime. We do not see evidence that C 2 H and HCN formation are enhanced by CO depletion, possibly because the gas is already quite under-abundant in CO. Further CO depletion may actually hinder their production by limiting the gas-phase carbon supply. The embedded sources show several chemical differences compared to the Class II stage, which seem to arise from shielding of radiation by the envelope (impacting C 2 H formation and HC 15 N fractionation) and sublimation of ices from infalling material (impacting HCN and C 18 O abundances). Such chemical differences between Class 0/I and Class II sources may affect the volatile composition of planet-forming material at different stages in the disk lifetime.

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“…Recent high-resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of H 2 CO transitions in 20 protoplanetary disks suggest that both gas-phase and solid-state formation of formaldehyde occurs, with their relative contributions varying across different disks (van der Marel et al 2014;Loomis et al 2015;Carney et al 2017;Öberg et al 2017;Guzmán et al 2018;Kastner et al 2018;Podio et al 2019;Garufi et al 2020;Pegues et al 2020). Parametric model fits to resolved observations of H 2 CO 3 12 -2 11 and 5 15 -4 14 in the disk of TTauri star TWHya find both warm and cold H 2 CO components in compact and extended regions, respectively (Öberg et al 2017).…”

Section: Introductionmentioning

confidence: 99%

The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

Scheltinga

Hogerheijde

Cleeves

et al. 2021

ApJ

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Formaldehyde (H 2 CO) is an important precursor to organics like methanol (CH 3 OH). It is important to understand the conditions that produce H 2 CO and prebiotic molecules during star and planet formation. H 2 CO possesses both gas-phase and solid-state formation pathways, involving either UV-produced radical precursors or CO ice and cold (20 K) dust grains. To understand which pathway dominates, gaseous H 2 COʼs ortho-to-para ratio (OPR) has been used as a probe, with a value of 3 indicating "warm" conditions and <3 linked to cold formation in the solid state. We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of multiple ortho-and para-H 2 CO transitions in the TWHya protoplanetary disk to test H 2 CO formation theories during planet formation. We find disk-averaged rotational temperatures and column densities of 33±2 K, (1.1±0.1)× 10 12 cm −2 and 25±2 K, (4.4±0.3)×10 11 cm −2 for ortho-and para-H 2 CO, respectively, and an OPR of 2.49±0.23. A radially resolved analysis shows that the observed H 2 CO emits mostly at rotational temperatures of 30-40 K, corresponding to a layer with z/R0.25. The OPR is consistent with 3 within 60 au, the extent of the pebble disk, and decreases beyond 60 au to 2.0±0.5. The latter corresponds to a spin temperature of 12 K, well below the rotational temperature. The combination of relatively uniform emitting conditions, a radial gradient in the OPR, and recent laboratory experiments and theory on OPR ratios after sublimation, led us to speculate thatgas-phase formation is responsible for the observed H 2 CO across the TWHya disk.

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An ALMA Survey of H₂CO in Protoplanetary Disks

Cited by 68 publications

References 81 publications

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

An Evolutionary Study of Volatile Chemistry in Protoplanetary Disks

The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

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An ALMA Survey of H2CO in Protoplanetary Disks

Cited by 68 publications

References 81 publications

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

An Evolutionary Study of Volatile Chemistry in Protoplanetary Disks

The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation

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An ALMA Survey of H₂CO in Protoplanetary Disks