Formation of Organic Molecules and Water in Warm Disk Atmospheres

Najita, J.; Ádámkovics, Máté; Glassgold, A. E.

doi:10.1088/0004-637x/743/2/147

Cited by 67 publications

(119 citation statements)

References 59 publications

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“…Conversely, thermochemical models predict relatively low CO 2 concentrations 20,32 in the planet-forming regions of protoplanetary disks. Indeed, the high concentration of CO 2 (and other species) in interstellar ices has long been seen as strong evidence for the action of surface chemistry 33 .…”

Section: Discussionmentioning

confidence: 98%

“…There are still a number of simplifying assumptions in order to keep the problem contained. For instance, we set the gas temperature to that of the dust which is a good approximation for the hydrogen column density of the molecular layer at mid-infrared wavelengths (> 10 22 ) 20 . For atomic species and highly optically thick transitions probing higher layers, this approximation would likely be less valid.…”

Section: Previously Derived Inner Disk Concentrationsmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 98%

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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“…The warm gas chemistry in the photospheres of disks follows a similar chemical scheme as that in other interstellar regions with high temperature gas such as the inner envelopes of massive protostars (e.g., Lahuis & van Dishoeck 2000;Doty et al 2002;Rodgers & Charnley 2003;Stäuber et al 2005), Upper panel: abundance ratios in the disk model by Markwick et al (2002) at 5 AU (green triangle), from the reference disk model at 1 AU by Najita et al (2011) (blue square) and at a O/C = 1 (blue cross), and from the disk model by Agúndez et al (2008) at 1 AU (green square) and 3 AU (green cross). Lower panel: observed range of cometary abundance ratios from Mumma & Charnley (2011, green bar and stars). high density photodissociation regions (PDRs; e.g., Sternberg & Dalgarno 1995) and shocks (e.g., Mitchell 1984;Pineau des Forêts et al 1987;Viti et al 2011).…”

Section: Warm Chemistrymentioning

confidence: 88%

Exploring organic chemistry in planet-forming zones

Bast

Lahuis

Dishoeck

et al. 2013

A&A

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Context. Over the last few years, the chemistry of molecules other than CO in the planet-forming zones of disks is starting to be explored with Spitzer and high-resolution ground-based data. However, these studies have focused only on a few simple molecules. Aims. The aim of this study is to put observational constraints on the presence of more complex organic and sulfur-bearing molecules predicted to be abundant in chemical models of disks and to simulate high resolution spectra in view of future missions. Methods. High signal-to-noise ratio (S/N) Spitzer spectra of the near edge-on disks IRS 46 and GV Tau are used to search for midinfrared absorption bands of various molecules. These disks are good laboratories because absorption studies do not suffer from low line/continuum ratios that plague emission data. Simple local thermodynamic equilibrium (LTE) slab models are used to infer column densities (or upper limits) and excitation temperatures. Results. Mid-infrared bands of HCN, C 2 H 2 and CO 2 are clearly detected toward both sources. The HCN and C 2 H 2 absorption arises in warm gas with excitation temperatures of 400−700 K, whereas the CO 2 absorption originates in cooler gas of ∼250 K. Column densities and their ratios are comparable for the two sources. No other absorption features are detected at the 3σ level. Column density limits of the majority of molecules predicted to be abundant in the inner disk -C 2 H 4 , C 2 H 6 , C 6 H 6 , C 3 H 4 , C 4 H 2 , CH 3 , HNC, HC 3 N, CH 3 CN, NH 3 and SO 2 -are determined and compared with disk models. Conclusions. The inferred abundance ratios and limits with respect to C 2 H 2 and HCN are roughly consistent with models of the chemistry in high temperature gas. Models of UV irradiated disk surfaces generally agree better with the data than pure X-ray models. The limit on NH 3 /HCN implies that evaporation of NH 3 -containing ices is only a minor contributor. The inferred abundances and their limits also compare well with those found in comets, suggesting that part of the cometary material may derive from warm inner disk gas. The high resolution simulations show that future instruments on the James Webb Space Telescope (JWST), the Extremely Large Telescopes (ELTs), the Stratospheric Observatory for Infrared Astronomy (SOFIA) and the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) can probe up to an order of magnitude lower abundance ratios and put important new constraints on the models, especially if pushed to high S/Ns.

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“…Water emission at Spitzer wavelengths has been interpreted in most disks as coming from an optically thick surface layer within the snow line radius, at temperatures of 300-700 K Salyk et al 2011a). Modeling of the velocity unresolved Spitzer spectra (Δv ∼ 400 km s −1 ) provided estimates of the disk emitting region to the inner few au in disks (e.g., Najita et al 2011;Antonellini et al 2015;Walsh et al 2015). At 12.4 μm, within the Spitzer-IRS range, a few water lines have been resolved in velocity in four disks with VLT-VISIR and Gemini-TEXES (Δv ∼ 15 and ∼ 3.5 km s −1 , respectively; Lagage et al 2004;Lacy et al 2002), providing support to the emitting regions estimated by models for the Spitzer spectra (Pontoppidan et al 2010b;Banzatti et al 2014;Salyk et al 2015).…”

Section: An Unsolved Mystery From Water Surveys: Low Detections In DImentioning

confidence: 99%

The Depletion of Water During Dispersal of Planet-Forming Disk Regions

Banzatti

Pontoppidan

Salyk

et al. 2017

ApJ

121

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We present a new velocity-resolved survey of 2.9 μm spectra of hot H 2 O and OH gas emission from protoplanetary disks, obtained with the Cryogenic Infrared Echelle Spectrometer at the VLT (R ∼ 96,000). With the addition of archival Spitzer-IRS spectra, this is the most comprehensive spectral data set of water vapor emission from disks ever assembled. We provide line fluxes at 2.9-33 μm that probe from the dust sublimation radius at ∼0.05 au out to the region of the water snow line. With a combined data set for 55 disks, we find a new correlation between H 2 O line fluxes and the radius of CO gas emission, as measured in velocity-resolved 4.7 μm spectra (Rco), which probes molecular gaps in inner disks. We find that H 2 O emission disappears from 2.9 μm (hotter water) to 33 μm (colder water) as R co increases and expands out to the snow line radius. These results suggest that the infrared water spectrum is a tracer of inside-out water depletion within the snow line. It also helps clarify an unsolved discrepancy between water observations and models by finding that disks around stars ofgenerally have inner gaps with depleted molecular gas content. We measure radial trends in H 2 O, OH, and CO line fluxes that can be used as benchmarks for models to study the chemical composition and evolution of planet-forming disk regions at 0.05-20 au. We propose that JWST spectroscopy of molecular gas may be used as a probe of inner disk gas depletion, complementary to the larger gaps and holes detected by direct imaging and by ALMA.

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Formation of Organic Molecules and Water in Warm Disk Atmospheres

Cited by 67 publications

References 59 publications

The chemistry of planet-forming regions is not interstellar

The chemistry of planet-forming regions is not interstellar

Exploring organic chemistry in planet-forming zones

The Depletion of Water During Dispersal of Planet-Forming Disk Regions

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