A New Raytracer for Modeling Au-Scale Imaging of Lines From Protoplanetary Disks

Pontoppidan, K. M.; Meijerink, R.; Dullemond, C. P.; Blake, Geoffrey A.

doi:10.1088/0004-637x/704/2/1482

Cited by 37 publications

(51 citation statements)

References 56 publications

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“…The preferred method for comparing model results with observations is the simulation of the line emission; however, this is a non-trivial matter involving careful consideration of collisional and radiative excitation in the IR (see, e.g., Pontoppidan et al 2009;Meijerink et al 2009;Thi et al 2013;Bruderer et al 2015). Moreover, the dust properties and size distribution (including, e.g., grain growth) become crucial for the calculation of the emitted spectrum (see, e.g., Meijerink et al 2009).…”

Section: Comparison With Observed Trendsmentioning

confidence: 99%

The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime

Walsh

Nomura

Dishoeck

2015

A&A

185

329

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Context. Near-to mid-infrared observations of molecular emission from protoplanetary disks show that the inner regions are rich in small organic volatiles (e.g., C 2 H 2 and HCN). Trends in the data suggest that disks around cooler stars (T eff ≈ 3000 K) are potentially (i) more carbon-rich; and (ii) more molecule-rich than their hotter counterparts (T eff > ∼ 4000 K). Aims. We explore the chemical composition of the planet-forming region (<10 AU) of protoplanetary disks around stars over a range of spectral types (from M dwarf to Herbig Ae) and compare with the observed trends. Methods. Self-consistent models of the physical structure of a protoplanetary disk around stars of different spectral types are coupled with a comprehensive gas-grain chemical network to map the molecular abundances in the planet-forming zone. The effects of (i) N 2 self shielding; (ii) X-ray-induced chemistry; and (iii) initial abundances, are investigated. The chemical composition in the "observable" atmosphere is compared with that in the disk midplane where the bulk of the planet-building reservoir resides. Results. M dwarf disk atmospheres are relatively more molecule rich than those for T Tauri or Herbig Ae disks. The weak far-UV flux helps retain this complexity which is enhanced by X-ray-induced ion-molecule chemistry. N 2 self shielding has only a small effect in the disk molecular layer and does not explain the higher C 2 H 2 /HCN ratios observed towards cooler stars. The models underproduce the OH/H 2 O column density ratios constrained in Herbig Ae disks, despite reproducing (within an order of magnitude) the absolute value for OH: the inclusion of self shielding for H 2 O photodissociation only increases this discrepancy. One possible explanation is the adopted disk structure. Alternatively, the "hot" H 2 O (T > ∼ 300 K) chemistry may be more complex than assumed. The results for the atmosphere are independent of the assumed initial abundances; however, the composition of the disk midplane is sensitive to the initial main elemental reservoirs. The models show that the gas in the inner disk is generally more carbon rich than the midplane ices. This effect is most significant for disks around cooler stars. Furthermore, the atmospheric C/O ratio appears larger than it actually is when calculated using observable tracers only. This is because gas-phase O 2 is predicted to be a significant reservoir of atmospheric oxygen.Conclusions. The models suggest that the gas in the inner regions of disks around cooler stars is more carbon rich; however, calculations of the molecular emission are necessary to definitively confirm whether the chemical trends reproduce the observed trends.

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Section: Comparison With Observed Trendsmentioning

confidence: 99%

The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime

Walsh

Nomura

Dishoeck

2015

A&A

185

329

View full text Add to dashboard Cite

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“…Also, we have implemented a stepsize adjustment along the rays, which avoids that the raytracer takes too small steps in regions where the line does not intersect with the frequency of the current channel due to the velocity profile. This method is similar to the technique implemented in RadLite (Pontoppidan et al 2009) and speeds up the raytracing considerably.…”

Section: A3 Raytracingmentioning

confidence: 99%

“…We have compared the results of the raytracer with the analytical results and find agreement to within a few percent, independent of the inclination of the disk. We note this is a meaningful benchmark test, as strong velocity gradients in the inner disk require an accurate step-size adjustment along the ray in order not to miss narrow lines (Pontoppidan et al 2009). …”

Section: A3 Raytracingmentioning

confidence: 99%

Survival of molecular gas in cavities of transition disks

Bruderer

2013

A&A

197

310

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Context. Planet formation is closely related to the structure and dispersal of protoplanetary disks. A certain class of disks, called transition disks, exhibit cavities in dust images at scales of up to a few 10s of AU. The formation mechanism of the cavities is still unclear. The gas content of such cavities can be spatially resolved for the first time using the Atacama Large Millimeter/submillimeter Array (ALMA). Aims. We develop a new series of models to simulate the physical conditions and chemical abundances of the gas in cavities to address the question whether the gas is primarily atomic or molecular inside the dust free cavities exposed to intense UV radiation. Molecular/atomic line emission by carbon monoxide (CO), its isotopologues ( Methods. We use a thermo-chemical model, which calculates the radiative transfer both in lines and the continuum, and solves for the chemical abundances and gas temperature. The model is based on our previous work, but includes several improvements. We study the dependence of CO abundances and lines on several parameters such as gas mass in the cavity, disk mass and luminosity of the star.Results. The gas can remain in molecular form down to very low amounts of gas in the cavity (∼1% of M Earth ). Shielding of the stellar radiation by a dusty inner disk ("pre-transition disk") allows CO to survive down to lower gas masses in the cavity. The column densities of H 2 and CO in the cavity scale almost linearly with the amount of gas in the cavity down to the mass where photodissociation becomes important. The main parameter for the CO emission from cavity is the gas mass. Other parameters such as the outer disk mass, bolometric luminosity, shape of the stellar spectrum or PAH abundance are less important. Since the CO pure rotational lines readily become optically thick, the CO isotopologues need to be observed in order to quantitatively determine the amount of gas in the cavity. Determining gas masses in the cavity from atomic lines (Conclusions. A wide range of gas masses in the cavity of transition disks (∼4 orders of magnitude) can be probed using combined observations of CO isotopologue lines with ALMA. Measuring the gas mass in the cavity will ultimately help to distinguish between different cavity formation theories.

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“…In particular, the higher-order model yields estimates for the absolute local concentration in the disk photospheres (n(X)/n(H)). The modeling procedure is based on the commonly used continuum radiative transfer code RADMC 18 , along with the line raytracer, RADLite 19 . There are still a number of simplifying assumptions in order to keep the problem contained.…”

Section: Previously Derived Inner Disk Concentrationsmentioning

confidence: 99%

The chemistry of planet-forming regions is not interstellar

Pontoppidan

Blevins

2014

Faraday Discuss.

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Advances in infrared and submillimeter technology have allowed for detailed observations of the molecular content of the planet-forming regions of protoplanetary disks. In particular, disks around solar-type stars now have growing molecular inventories that can be directly compared with both prestellar chemistry and that inferred for the early solar nebula. The data directly address the old question whether the chemistry of planet-forming matter is similar or different and unique relative to the chemistry of dense clouds and protostellar envelopes. The answer to this question may have profound consequences for the structure and composition of planetary systems. The practical challenge is that observations of emission lines from disks do not easily translate into chemical concentrations. Here, we present a two-dimensional radiative transfer model of RNO 90, a classical protoplanetary disk around a solar-mass star, and retrieve the concentrations of dominant molecular carriers of carbon, oxygen and nitrogen in the terrestrial region around 1 AU. We compare our results to the chemical inventory of dense clouds and protostellar envelopes, and argue that inner disk chemistry is, as expected, fundamentally different from prestellar chemistry. We find that the clearest discriminant may be the concentration of CO 2 , which is extremely low in disks, but one of the most abundant constituents of dense clouds and protostellar envelopes.

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A New Raytracer for Modeling Au-Scale Imaging of Lines From Protoplanetary Disks

Cited by 37 publications

References 56 publications

The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime

The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime

Survival of molecular gas in cavities of transition disks

The chemistry of planet-forming regions is not interstellar

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