Molecules with ALMA at Planet-forming Scales (MAPS). XV. Tracing Protoplanetary Disk Structure within 20 au

Context. Vertically hydrostatic protoplanetary disk models are based on the assumption that the main heating source, stellar irradiation, does not vary much with time. However, it is known that accreting young stars are variable sources of radiation. This is particularly evident for outbursting sources such as EX Lupi and FU Orionis stars. Aims. We investigate how such outbursts affect the vertical structure of the outer regions of the protoplanetary disk, in particular their appearance in scattered light at optical and near-infrared wavelengths. Methods. We employ the 3D FARGOCA radiation-hydrodynamics code, in polar coordinates, to compute the time-dependent behavior of the axisymmetric disk structure. The temperature is computed self-consistently and time-dependently from the irradiation flux using a two-stage radiative transfer method: first the direct illumination is computed; then the diffuse radiation is treated with the flux-limited diffusion method. The outbursting inner disk region is not included explicitly. Instead, its luminosity is added to the stellar luminosity and is thus included in the irradiation of the outer disk regions. For time snapshots of interest we insert the density structure into the RADMC-3D radiative transfer code and compute the appearance of the disk at optical/near-infrared wavelengths, where we observe stellar light that is scattered off the surface of the disk. Results. We find that, depending on the amplitude of the outbursts, the vertical structure of the disk can become highly dynamic, featuring circular surface waves of considerable amplitude. These “hills” and “valleys” on the disk’s surface show up in the scattered light images as bright and dark concentric rings. Initially these rings are small and act as standing waves, but they subsequently lead to outward propagating waves, like the waves produced by a stone thrown into a pond. These waves continue long after the actual outburst has died out. Conclusions. Single, periodic, or quasiperiodic outbursts of the innermost regions of protoplanetary disks will necessarily lead to wavy structures on the surface of these disks at all radii. We propose that some of the multi-ringed structures seen in optical/infrared images of several protoplanetary disks may have their origin in outbursts that occurred decades or centuries ago. However, the multiple rings seen at (sub-)millimeter wavelengths in HL Tau and several other disks are not expected to be related to such waves.

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Global Protoplanetary Disk Simulations: Dead Zone Formation and FUor Outbursts

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319001650 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 324-325

Author(s):

Kundan Kadam ◽

E. Vorobyov ◽

Zs. Regály ◽

Á. Kóspál ◽

P. Ábráham

Keyword(s):

Molecular Cloud ◽

Dead Zone ◽

Protoplanetary Disk ◽

Model Parameters ◽

Zone Formation ◽

Hydrodynamic Simulations ◽

Disk Structure ◽

Self Consistent ◽

Disk Evolution ◽

Collapse Phase

AbstractWe conducted global hydrodynamic simulations of protoplanetary disk evolution with an adaptive Shakura-Sunyaev α prescription to represent the layered disk structure, and starting with the collapse phase of the molecular cloud. With the canonical values of model parameters, self-consistent dead zones formed at the scale of a few au. The instabilities associated with the dead zone and corresponding outbursts, similar to FUor eruptions, were also observed in the simulations.

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First detections of H13CO+ and HC15N in the disk around HD 97048

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834388 ◽

2019 ◽

Vol 629 ◽

pp. A75 ◽

Cited By ~ 4

Author(s):

Alice S. Booth ◽

Catherine Walsh ◽

John D. Ilee

Keyword(s):

Dust Emission ◽

Line Emission ◽

Abundance Ratio ◽

Protoplanetary Disk ◽

Temperature Structure ◽

Exchange Reactions ◽

Gas Kinematics ◽

Spatially Resolved ◽

Chemical Models ◽

Disk Structure

Observations of different molecular lines in protoplanetary disks provide valuable information on the gas kinematics, as well as constraints on the radial density and temperature structure of the gas. With ALMA we have detected H13CO+ (J = 4–3) and HC15N (J = 4–3) in the HD 97048 protoplanetary disk for the first time. We compare these new detections to the ringed continuum mm-dust emission and the spatially resolved CO (J = 3–2) and HCO+ (J = 4–3) emission. The radial distributions of the H13CO+ and HC15N emission show hints of ringed sub-structure whereas, the optically thick tracers, CO and HCO+, do not. We calculate the HCO+/H13CO+ intensity ratio across the disk and find that it is radially constant (within our uncertainties). We use a physio-chemical parametric disk structure of the HD 97048 disk with an analytical prescription for the HCO+ abundance distribution to generate synthetic observations of the HCO+ and H13CO+ disk emission assuming LTE. The best by-eye fit models require radial variations in the HCO+/H13CO+ abundance ratio and an overall enhancement in H13CO+ relative to HCO+. This highlights the need to consider isotope selective chemistry and in particular low temperature carbon isotope exchange reactions. This also points to the presence of a reservoir of cold molecular gas in the outer disk (T ≲ 10 K, R ≳ 200 au). Chemical models are required to confirm that isotope-selective chemistry alone can explain the observations presented here. With these data, we cannot rule out that the known dust substructure in the HD 97048 disk is responsible for the observed trends in molecular line emission, and higher spatial resolution observations are required to fully explore the potential of optically thin tracers to probe planet-carved dust gaps. We also report non-detections of H13CO+ and HC15N in the HD 100546 protoplanetary disk.

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Upper limits on CH3OH in the HD 163296 protoplanetary disk

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834353 ◽

2019 ◽

Vol 623 ◽

pp. A124 ◽

Cited By ~ 12

Author(s):

M. T. Carney ◽

M. R. Hogerheijde ◽

V. V. Guzmán ◽

C. Walsh ◽

K. I. Öberg ◽

...

Keyword(s):

Gas Phase ◽

Column Density ◽

Matched Filter ◽

Image Plane ◽

Protoplanetary Disk ◽

Chemical Complexity ◽

Disk Structure ◽

T Tauri ◽

Upper Limits ◽

Integrated Intensity

Context. Methanol (CH3OH) is at the root of organic ice chemistry in protoplanetary disks. Its connection to prebiotic chemistry and its role in the chemical environment of the disk midplane make it an important target for disk chemistry studies. However, its weak emission has made detections difficult. To date, gas-phase CH3OH is detected in only one Class II disk, TW Hya. Aims. We aim to constrain the methanol content of the HD 163296 protoplanetary disk. Methods. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to search for a total of four CH3OH emission lines in bands six and seven toward the disk around the young Herbig Ae star HD 163296. The disk-averaged column density of methanol and its related species formaldehyde (H2CO) were estimated assuming optically thin emission in local thermodynamic equilibrium. We compared these results to the gas-phase column densities of the TW Hya disk. Results. No targeted methanol lines were detected with Keplerian masking in the image plane nor with matched filter analysis in the uv plane individually nor after line stacking. The 3σ disk-integrated intensity upper limits are <51 mJy km s−1 for the band six lines and <26 mJy km s−1 for the band seven lines. The band seven lines provide the strictest 3σ upper limit on disk-averaged column density with Navg < 5.0 × 1011 cm−2. The methanol-to-formaldehyde ratio is CH3OH∕H2CO<0.24 in the HD 163296 disk compared to a ratio of 1.27 in the TW Hya disk. Conclusions. The HD 163296 protoplanetary disk is less abundant in methanol with respect to formaldehyde compared to the disk around TW Hya. Differences in the stellar irradiation in this Herbig Ae disk as compared to that of a disk around a T Tauri star likely influence the gaseous methanol and formaldehyde content. Possible reasons for the lower HD 163296 methanol-to-formaldehyde ratio include: a higher than expected gas-phase formation of H2CO in the HD 163296 disk, uncertainties in the grain surface formation efficiency of CH3OH and H2CO, and differences in the disk structure and/or CH3OH and H2CO desorption processes that drive the release of the molecules from ice mantles back into the gas phase. These results provide observational evidence that the gas-phase chemical complexity found in disks may be strongly influenced by the spectral type of the host star.

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Revisiting the case of R Monocerotis: Is CO removed at R < 20 au?

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731658 ◽

2018 ◽

Vol 617 ◽

pp. A31 ◽

Cited By ~ 2

Author(s):

T. Alonso-Albi ◽

P. Riviere-Marichalar ◽

A. Fuente ◽

S. Pacheco-Vázquez ◽

B. Montesinos ◽

...

Keyword(s):

Spectral Type ◽

Protoplanetary Disk ◽

Emission Lines ◽

Disk Model ◽

Dispersal Mechanism ◽

Disk Structure ◽

Upper Limits ◽

Intense Emission ◽

Uv Photons ◽

Continuum Data

Context. To our knowledge, R Mon is the only B0 star in which a gaseous Keplerian disk has been detected. However, there is some controversy about the spectral type of R Mon. Some authors propose that it could be a later B8e star, where disks are more common. Aims. Our goal is to re-evaluate the R Mon spectral type and characterize its protoplanetary disk. Methods. The spectral type of R Mon has been re-evaluated using the available continuum data and UVES emission lines. We used a power-law disk model to fit previous 12CO 1 →0 and 2 →1 interferometric observations and the PACS CO data to investigate the disk structure. Interferometric detections of 13CO J = 1 →0, HCO+ 1 →0, and CN 1 →0 lines using the IRAM Plateau de Bure Interferometer (PdBI) are presented. The HCN 1 →0 line was not detected. Results. Our analysis confirms that R Mon is a B0 star. The disk model compatible with the 12CO 1 →0 and 2 →1 interferometric observations falls short of predicting the observed fluxes of the 14 < Ju < 31 PACS lines; this is consistent with the scenario in which some contribution to these lines is coming from a warm envelope and/or UV-illuminated outflow walls. More interestingly, the upper limits to the fluxes of the Ju > 31 CO lines suggest the existence of a region empty of CO at R ≲ 20 au in the protoplanetary disk. The intense emission of the HCO+ and CN lines shows the strong influence of UV photons on gas chemistry. Conclusions. The observations gathered in this paper are consistent with the presence of a transition disk with a cavity of Rin ≳ 20 au around R Mon. This size is similar to the photoevaporation radius that supports the interpretation that UV photoevaporation is main disk dispersal mechanism in massive stars

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Sulphur monoxide exposes a potential molecular disk wind from the planet-hosting disk around HD 100546

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731347 ◽

2018 ◽

Vol 611 ◽

pp. A16 ◽

Cited By ~ 15

Author(s):

Alice S. Booth ◽

Catherine Walsh ◽

Mihkel Kama ◽

Ryan A. Loomis ◽

Luke T. Maud ◽

...

Keyword(s):

Line Profile ◽

Hot Spot ◽

Central Star ◽

Protoplanetary Disk ◽

Disk Wind ◽

North East ◽

The North ◽

Disk Structure ◽

Spectrally Resolved ◽

Accretion Shock

Sulphur-bearing volatiles are observed to be significantly depleted in interstellar and circumstellar regions. This missing sulphur is postulated to be mostly locked up in refractory form. With ALMA we have detected sulphur monoxide (SO), a known shock tracer, in the HD 100546 protoplanetary disk. Two rotational transitions: J = 77–66 (301.286 GHz) and J = 78–67 (304.078 GHz) are detected in their respective integrated intensity maps. The stacking of these transitions results in a clear 5σ detection in the stacked line profile. The emission is compact but is spectrally resolved and the line profile has two components. One component peaks at the source velocity and the other is blue-shifted by 5 km s−1. The kinematics and spatial distribution of the SO emission are not consistent with that expected from a purely Keplerian disk. We detect additional blue-shifted emission that we attribute to a disk wind. The disk component was simulated using LIME and a physical disk structure. The disk emission is asymmetric and best fit by a wedge of emission in the north-east region of the disk coincident with a “hot-spot” observed in the CO J = 3–2 line. The favoured hypothesis is that a possible inner disk warp (seen in CO emission) directly exposes the north-east side of the disk to heating by the central star, creating locally the conditions to launch a disk wind. Chemical models of a disk wind will help to elucidate why the wind is particularly highlighted in SO emission and whether a refractory source of sulphur is needed. An alternative explanation is that the SO is tracing an accretion shock from a circumplanetary disk associated with the proposed protoplanet embedded in the disk at 50 au. We also report a non-detection of SO in the protoplanetary disk around HD 97048.

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