Modeling Nitrogen Fractionation in the Protoplanetary Disk around TW Hya: Model Constraints on Grain Population and Carbon-to-Oxygen Elemental Abundance Ratio
arXiv:2012.12531 · doi:10.3847/1538-4357/abd633
Abstract
Observations conducted using the Atacama Large Millimeter/submillimeter Array on the protoplanetary disk around TW Hya show the nitrogen fractionation of HCN molecules in HCN/HCN 120 at a radius of 20 AU. In this study, we investigated the physical and chemical conditions that control this nitrogen fractionation process. To this end, a new disk model was developed, in which the isotope-selective photodissociation of N and isotope-exchange chemical reactions have been incorporated. Our model can successfully reproduce the observed HCN column density when the elemental abundances of the gas-phase carbon and oxygen are depleted by two orders of magnitude relative to those in the interstellar medium and carbon is more abundant than oxygen ([C/O] 1). The isotope-selective photodissociation of N is the dominant nitrogen fractionation process in our models. The observed HCN/HCN ratio, which increases outwards, can also be reproduced by the model by assuming that the small dust grains in the atmosphere of the outer disk are depleted more than those in the inner disk. This is consistent with grain evolution models, according to which small dust grains are continuously replenished in the inner disk due to fragmentation of the large dust grains that radially drift from the outer disk.
Accepted for publication in The Astrophysical Journal
References in corpus (30)
- Monte Carlo radiative transfer in protoplanetary disks
- Radiative transfer in very optically thick circumstellar disks
- Complex organic molecules in protoplanetary disks
- HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
- Constraining the X-ray and Cosmic Ray Ionization Chemistry of the TW Hya Protoplanetary Disk: Evidence for a Sub-interstellar Cosmic Ray Rate
- Three radial gaps in the disk of TW Hydrae imaged with SPHERE
- Protoplanetary disk masses from CO isotopologues line emission
- Heat and Dust in Active Layers of Protostellar Disks
- Hydrocarbon emission rings in protoplanetary disks induced by dust evolution
- Isotopic fractionation of carbon, deuterium and nitrogen : a full chemical study
- CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing
- Reprocessing of Ices in Turbulent Protoplanetary Disks: Carbon and Nitrogen Chemistry
- Resolving the chemistry in the disk of TW Hydrae I. Deuterated species
- Water vapor distribution in protoplanetary disks
- Exploring the Origins of Carbon in Terrestrial Worlds
- CN rings in full protoplanetary disks around young stars as probes of disk structure
- Direct evidence of multiple reservoirs of volatile nitrogen in a protosolar nebula analogue
- Sticking coefficient of hydrogen and deuterium on silicates under interstellar conditions
- An evolutionary study of volatile chemistry in protoplanetary disks
- Nitrogen Fractionation in Protoplanetary Disks from the H13CN/HC15N Ratio
- Unbiased mm-wave Line Surveys of TW Hya and V4046 Sgr: The Enhanced C2H and CN Abundances of Evolved Protoplanetary Disks
- Revised Models of Interstellar Nitrogen Isotopic Fractionation
- Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation
- A Ring of C2H in the Molecular Disk Orbiting TW Hya
- Chemical nitrogen fractionation in dense molecular clouds
- Unlocking CO Depletion in Protoplanetary Disks II. Primordial C/H Predictions Inside the CO Snowline
- The dry and carbon poor inner disk of TW Hya: evidence for a massive icy dust trap
- First Detection of HCN in the Interstellar Medium
- The warm CO gas along the UV-heated outflow cavity walls: a possible interpretation for the Herschel/PACS CO spectra of embedded YSOs
- A PDR model for the FIR mid- CO ladder with universal rotational temperature in star forming region