A Survey of CH<sub>3</sub>CN and HC<sub>3</sub>N in Protoplanetary Disks

Bergner, Jennifer B.; Guzmán, Viviana V.; Öberg, Karin I.; Loomis, Ryan A.; Pegues, Jamila

doi:10.3847/1538-4357/aab664

Cited by 120 publications

(133 citation statements)

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“…We find an approximate CH 3 CN/CH 3 OH column density ratio of unity, which is substantially higher than the few percent found in comets and around protostars (Mumma & Charnley 2011;Bergner et al 2017). As discussed in Bergner et al (2018), two scenarios could explain this finding: a higher photodesorption efficiency for CH 3 CN than CH 3 OH (where both species could either be inherited from the protostellar stage or form through in situ grain-surface chemistry), or gas-phase production of nitriles such as CH 3 CN could be enhanced by a high C/O ratio as discussed in Section 4.1.3. Thus although our observations are inconsistent with preserved interstellar abundance ratios, it is possible that inheritance contributes to the total CH 3 CN abundance in TW Hya.…”

Section: Implications For Cometary Ch 3 Cn Abundancesmentioning

confidence: 44%

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The Distribution and Excitation of CH₃CN in a Solar Nebula Analog

Loomis

Cleeves

Öberg

et al. 2018

ApJ

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110

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Cometary studies suggest that the organic composition of the early Solar Nebula was rich in complex nitrile species such CH 3 CN. Recent ALMA detections in protoplanetary disks suggest that these species may be common during planet and comet formation, but connecting gas-phase measurements to cometary abundances first requires constraints on formation chemistry and distributions of these species. We present here the detection of seven spatially resolved transitions of CH 3 CN in the protoplanetary disk around the T-Tauri star TW Hya. Using a rotational diagram analysis, we find a disk-averaged column density of A radially resolved rotational diagram shows the rotational temperature to be constant across the disk, suggesting that the CH 3 CN emission originates from a layer at z/r∼0.3. Through comparison of the observations with predictions from a disk chemistry model, we find that grain-surface reactions likely dominate CH 3 CN formation and that in situ disk chemistry is sufficient to explain the observed CH 3 CN column density profile without invoking inheritance from the protostellar phase. However, the same model fails to reproduce a solar system cometary abundance of CH 3 CN relative to H 2 O in the midplane, suggesting that either vigorous vertical mixing or some degree of inheritance from interstellar ices occurred in the Solar Nebula.

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Section: Implications For Cometary Ch 3 Cn Abundancesmentioning

confidence: 44%

“…Larger nitriles such as HC 3 N have only been found more recently (Chapillon et al 2012), and ALMA is just now beginning to reveal more complex species, such as CH 3 CN Bergner et al 2018). The provenance of these species in disks is unclear, however, and will play a role in setting their final abundances in the forming cometary bodies.…”

Section: Introductionmentioning

confidence: 99%

The Distribution and Excitation of CH₃CN in a Solar Nebula Analog

Loomis

Cleeves

Öberg

et al. 2018

ApJ

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110

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“…We used the median of the standard deviations as the estimate of the line emission map's noise (σ map ). See Bergner et al (2018) for the full methodology for generating rms maps.…”

Section: Data Reductionmentioning

confidence: 99%

“…In this process, we deprojected the disks and divided them into 0.1" rings about the host star, and then averaged the emission within each ring. Following Bergner et al (2018), we estimated the noise within each ring as (σ map / √ N ), where N is the number of independent measurements in this ring, taken to be the number of pixels in the ring divided by the beam area (in pixels). For rings within the beam's circumference, we fixed N to be the beam circumference (in pixels) divided by the beam area.…”

Section: Data Reductionmentioning

confidence: 99%

An ALMA Survey of H₂CO in Protoplanetary Disks

Pegues

Öberg

Bergner

et al. 2020

ApJ

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106

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H 2 CO is one of the most abundant organic molecules in protoplanetary disks and can serve as a precursor to more complex organic chemistry. We present an ALMA survey of H 2 CO towards 15 disks covering a range of stellar spectral types, stellar ages, and dust continuum morphologies. H 2 CO is detected towards 13 disks and tentatively detected towards a 14th. We find both centrally-peaked and centrally-depressed emission morphologies, and half of the disks show ring-like structures at or beyond expected CO snowline locations. Together these morphologies suggest that H 2 CO in disks is commonly produced through both gas-phase and CO-ice-regulated grain-surface chemistry. We extract disk-averaged and azimuthally-averaged H 2 CO excitation temperatures and column densities for four disks with multiple H 2 CO line detections. The temperatures are between 20-50K, with the exception of colder temperatures in the DM Tau disk. These temperatures suggest that H 2 CO emission in disks is generally emerging from the warm molecular layer, with some contributions from the colder midplane. Applying the same H 2 CO excitation temperatures to all disks in the survey, we find that H 2 CO column densities span almost three orders of magnitude (∼ 5×10 11 −5×10 14 cm −2 ). The column densities appear uncorrelated with disk size and stellar age, but Herbig Ae disks may have less H 2 CO compared to T Tauri disks, possibly because of less CO freeze-out. More H 2 CO observations towards Herbig Ae disks are needed to confirm this tentative trend, and to better constrain under which disk conditions H 2 CO and other oxygen-bearing organics efficiently form during planet formation.

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“…Protoplanetary disks: In protoplanetary disks, very few iCOMs have been detected so far: methanol (CH 3 OH), methyl cyanide (CH 3 CN) and formic acid (HCOOH) [66][67][68] . The obvious ques-7 tion is: are more complex molecules not detected in protoplanetary disks only because of the current instrument detection limits or chemistry changes from the Class 0 to the protoplanetary disk phase?…”

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confidence: 99%

Astrochemistry as a Tool To Follow Protostellar Evolution: The Class I Stage

Bianchi

Ceccarelli

Codella

et al. 2019

ACS Earth Space Chem.

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The latest developments in astrochemistry have shown how some molecular species can be used as a tool to study the early stages of the solar-type star formation process. Among them, the more relevant species are the interstellar complex organic molecules (iCOMs) and the deuterated molecules. Their analysis give us information on the present and past history of protostellar objects. Among the protostellar evolutionary stages, Class I protostars represent a perfect laboratory in which to study the initial conditions for the planet formation process. Indeed, from a physical point of view, the Class I stage is the bridge between the Class 0 phase, dominated by the accretion process, and the protoplanetary disk phase, when planets form. Despite their importance, few observations of Class I protostars exist and very little is known about their chemical content. In this paper we review the (few) existing observations of iCOMs and deuterated species in Class I protostars. In addition, we present new observations of deuterated cyanoacetylene and thioformaldehyde towards the Class I protostar SVS13-A. These new observations allow us to better understand the physical and chemical structure of SVS13-A and compare the cyanoacetylene and thioformaldehyde deuteration with other sources in different evolutionary phases. stellar complex organic molecules cessing occurs during the birth of a planetary system like our Solar System and which molecules are inherited from the early stages.In this context, the Class I protostars represent a crucial phase: they are the bridge between the youngest protostars, dominated by the gravitational collapse, and the more evolved planetary disks, where planets and comets form. In addition, as we will discuss in detail in the next section, mounting evidence shows that planets/comets formation occurs very early, likely already in the Class I phase.In this article, we will review what we know so far about the chemical content of Class I protostars, with a particular focus on iCOMs and deuterated molecules. We will then present new observations towards the prototype Class I source, SVS13-A, which allow us to better understand its structure and its deuterated molecular content. The structure of this article is the following: in Section 2, we describe why Class I protostars are crucial in the evolution of solar-type systems; in Section 3, we report an overview of the previous observations of iCOMs and deuterated molecules towards Class I protostars; in Section 4, we present new observations of HC 3 N, DC 3 N, H 2 CS and HDCS towards SVS13-A and we discuss their implications in our understanding of Class I protostars; Section 5 concludes providing the future perspectives in the study of Class I protostars. Class I sources, a crucial intermediate evolutionary phase inthe formation of solar-type systems 2.1 Physical evolution of a solar-type protostarThe formation of a solar-type star is a complex process which lasts some Myr. It starts in dense filaments of molecular clouds and is governed by the interpla...

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A Survey of CH₃CN and HC₃N in Protoplanetary Disks

Cited by 120 publications

References 46 publications

The Distribution and Excitation of CH₃CN in a Solar Nebula Analog

The Distribution and Excitation of CH₃CN in a Solar Nebula Analog

An ALMA Survey of H₂CO in Protoplanetary Disks

Astrochemistry as a Tool To Follow Protostellar Evolution: The Class I Stage

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A Survey of CH3CN and HC3N in Protoplanetary Disks

Cited by 120 publications

References 46 publications

The Distribution and Excitation of CH3CN in a Solar Nebula Analog

The Distribution and Excitation of CH3CN in a Solar Nebula Analog

An ALMA Survey of H2CO in Protoplanetary Disks

Astrochemistry as a Tool To Follow Protostellar Evolution: The Class I Stage

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A Survey of CH₃CN and HC₃N in Protoplanetary Disks

The Distribution and Excitation of CH₃CN in a Solar Nebula Analog

The Distribution and Excitation of CH₃CN in a Solar Nebula Analog

An ALMA Survey of H₂CO in Protoplanetary Disks