Chemistry in disks

Dutrey, Anne; Henning, Th.; Guilloteau, S.; Semenov, D.; Piétu, V.; Schreyer, K.; Bacmann, A.; Launhardt, R.; Pety, J.; Gueth, F.

doi:10.1051/0004-6361:20065385

Cited by 94 publications

(156 citation statements)

References 43 publications

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“…Dutrey et al 2014) and are commonly used to trace the ionization structure of disks (e.g. Dutrey et al 2007;Öberg et al 2011b;Cleeves et al 2015). Also Ceccarelli et al (2014) used these two molecules to trace SPs in a protostellar envelope.…”

Section: Impact On Hco + and N 2 H +mentioning

confidence: 99%

Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

Rab

Güdel

Padovani

et al. 2017

A&A

102

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Context. Anomalies in the abundance measurements of short lived radionuclides in meteorites indicate that the protosolar nebulae was irradiated by a high amount of energetic particles (E 10 MeV). The particle flux of the contemporary Sun cannot explain these anomalies. However, similar to T Tauri stars the young Sun was more active and probably produced enough high energy particles to explain those anomalies. Aims. We want to study the interaction of stellar energetic particles with the gas component of the disk (i.e. ionization of molecular hydrogen) and identify possible observational tracers of this interaction. Methods. We use a 2D radiation thermo-chemical protoplanetary disk code to model a disk representative for T Tauri stars. We use a particle energy distribution derived from solar flare observations and an enhanced stellar particle flux proposed for T Tauri stars. For this particle spectrum we calculate the stellar particle ionization rate throughout the disk with an accurate particle transport model. We study the impact of stellar particles for models with varying X-ray and cosmic-ray ionization rates. Results. We find that stellar particle ionization has a significant impact on the abundances of the common disk ionization tracers HCO + and N 2 H + , especially in models with low cosmic-ray ionization rates (e.g. 10 −19 s −1 for molecular hydrogen). In contrast to cosmic rays and X-rays, stellar particles cannot reach the midplane of the disk. Therefore molecular ions residing in the disk surface layers are more affected by stellar particle ionization than molecular ions tracing the cold layers/midplane of the disk. Conclusions. Spatially resolved observations of molecular ions tracing different vertical layers of the disk allow to disentangle the contribution of stellar particle ionization from other competing ionization sources. Modeling such observations with a model like the one presented here allows to constrain the stellar particle flux in disks around T Tauri stars.

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Section: Impact On Hco + and N 2 H +mentioning

confidence: 99%

Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

Rab

Güdel

Padovani

et al. 2017

A&A

102

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“…In dense clouds well shielded from UV radiation, most nitrogen is expected to exist as N 2 (e.g., Herbst & Klemperer 1973;Woodall et al 2007) but can only be detected indirectly through the protonated ion N 2 H + (Turner 1974;Herbst et al 1977) or its deuterated form N 2 D + . N 2 H + emission is indeed widely observed in dense cores (e.g., Bergin et al 2002;Crapsi et al 2005), star-forming regions (Fontani et al 2011;Tobin et al 2012), protoplanetary disks (Dutrey et al 2007;Öberg et al 2010) and external galaxies A&A 555, A14 (2013) (Mauersberger & Henkel 1991;Meier & Turner 2005;Muller et al 2011).…”

Section: Introductionmentioning

confidence: 95%

Photodissociation of interstellar N₂

Heays

Visser

et al. 2013

A&A

138

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Context. Molecular nitrogen is one of the key species in the chemistry of interstellar clouds and protoplanetary disks, but its photodissociation under interstellar conditions has never been properly studied. The partitioning of nitrogen between N and N 2 controls the formation of more complex prebiotic nitrogen-containing species. Aims. The aim of this work is to gain a better understanding of the interstellar N 2 photodissociation processes based on recent detailed theoretical and experimental work and to provide accurate rates for use in chemical models. Methods. We used an approach similar to that adopted for CO in which we simulated the full high-resolution line-by-line absorption + dissociation spectrum of N 2 over the relevant 912-1000 Å wavelength range, by using a quantum-mechanical model which solves the coupled-channels Schrödinger equation. The simulated N 2 spectra were compared with the absorption spectra of H 2 , H, CO, and dust to compute photodissociation rates in various radiation fields and shielding functions. The effects of the new rates in interstellar cloud models were illustrated for diffuse and translucent clouds, a dense photon dominated region and a protoplanetary disk. Results. The unattenuated photodissociation rate in the Draine (1978, ApJS, 36, 595) radiation field assuming an N 2 excitation temperature of 50 K is 1.65 × 10 −10 s −1 , with an uncertainty of only 10%. Most of the photodissociation occurs through bands in the 957-980 Å range. The N 2 rate depends slightly on the temperature through the variation of predissociation probabilities with rotational quantum number for some bands. Shielding functions are provided for a range of H 2 and H column densities, with H 2 being much more effective than H in reducing the N 2 rate inside a cloud. Shielding by CO is not effective. The new rates are 28% lower than the previously recommended values. Nevertheless, diffuse cloud models still fail to reproduce the possible detection of interstellar N 2 except for unusually high densities and/or low incident UV radiation fields. The transition of N → N 2 occurs at nearly the same depth into a cloud as that of C + → C → CO. The orders-of-magnitude lower N 2 photodissociation rates in clouds exposed to black-body radiation fields of only 4000 K can qualitatively explain the lack of active nitrogen chemistry observed in the inner disks around cool stars. Conclusions. Accurate photodissociation rates for N 2 as a function of depth into a cloud are now available that can be applied to a wide variety of astrophysical environments.

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“…The aperture mask is then larger than the emitting area in any given channel, adding noise to the extracted spectrum. To combat this, a spatio-kinematic mask specifically tailored to the structure of the source may be used to reduce the amount of added noise (e.g., Dutrey et al 2007;Loomis et al 2015;Öberg et al 2015;Yen et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Detecting Weak Spectral Lines in Interferometric Data through Matched Filtering

Loomis

Öberg

Andrews

et al. 2018

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Modern radio interferometers enable observations of spectral lines with unprecedented spatial resolution and sensitivity. In spite of these technical advances, many lines of interest are still at best weakly detected and therefore necessitate detection and analysis techniques specialized for the low signal-to-noise ratio (S/N) regime. Matched filters can leverage knowledge of the source structure and kinematics to increase sensitivity of spectral line observations. Application of the filter in the native Fourier domain improves S/N while simultaneously avoiding the computational cost and ambiguities associated with imaging, making matched filtering a fast and robust method for weak spectral line detection. We demonstrate how an approximate matched filter can be constructed from a previously observed line or from a model of the source, and we show how this filter can be used to robustly infer a detection significance for weak spectral lines. When applied to ALMA Cycle 2 observations of CH 3 OH in the protoplanetary disk around TW Hya, the technique yields a ≈53% S/N boost over aperture-based spectral extraction methods, and we show that an even higher boost will be achieved for observations at higher spatial resolution. A Python-based open-source implementation of this technique is available under the MIT license at https://github.com/AstroChem/VISIBLE.

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Chemistry in disks

Cited by 94 publications

References 43 publications

Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

Photodissociation of interstellar N₂

Detecting Weak Spectral Lines in Interferometric Data through Matched Filtering

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Chemistry in disks

Cited by 94 publications

References 43 publications

Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

Stellar energetic particle ionization in protoplanetary disks around T Tauri stars

Photodissociation of interstellar N2

Detecting Weak Spectral Lines in Interferometric Data through Matched Filtering

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Product

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Photodissociation of interstellar N₂