Imaging of the CO Snow Line in a Solar Nebula Analog

Qi, Chunhua; Öberg, Karin I.; Wilner, David J.; D’Alessio, Paola; Bergin, Edwin A.; Andrews, Sean M.; Blake, Geoffrey A.; Hogerheijde, M. R.; Dishoeck, E. F. van

doi:10.1126/science.1239560

Cited by 302 publications

(362 citation statements)

References 51 publications

(37 reference statements)

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“…The depletion of CO and H 2 O in the quiescent phase thus allows N 2 H + to increase in abundance at almost all radii for the first few 1000 yr after the burst. This type of anti-correlation between CO and N 2 H + is well known from observations of molecular clouds, embedded protostars, and circumstellar disks (Bergin et al 2002;Jørgensen 2004;Qi et al 2013) and was also noted by Lee (2007). On timescales of more than a few 1000 yr, freeze-out of N 2 near 400 AU causes a decrease in the N 2 H + abundance.…”

Section: Abundance Profilesmentioning

confidence: 84%

Chemical tracers of episodic accretion in low-mass protostars

Visser

Bergin

Jørgensen

2015

A&A

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Aims. Accretion rates in low-mass protostars can be highly variable in time. Each accretion burst is accompanied by a temporary increase in luminosity, heating up the circumstellar envelope and altering the chemical composition of the gas and dust. This paper aims to study such chemical effects and discusses the feasibility of using molecular spectroscopy as a tracer of episodic accretion rates and timescales. Methods. We simulate a strong accretion burst in a diverse sample of 25 spherical envelope models by increasing the luminosity to 100 times the observed value. Using a comprehensive gas-grain network, we follow the chemical evolution during the burst and for up to 10 5 yr after the system returns to quiescence. The resulting abundance profiles are fed into a line radiative transfer code to simulate rotational spectra of C 18 O, HCO + , H 13 CO + , and N 2 H + at a series of time steps. We compare these spectra to observations taken from the literature and to previously unpublished data of HCO + and N 2 H + 6−5 from the Herschel Space Observatory. Results. The bursts are strong enough to evaporate CO throughout the envelope, which in turn enhances the abundance of HCO + and reduces that of N 2 H + . After the burst, it takes 10 3 -10 4 yr for CO to refreeze and for HCO + and N 2 H + to return to normal. The H 2 O snowline expands outwards by a factor of ∼10 during the burst; afterwards, it contracts again on a timescale of 10 2 -10 3 yr. The chemical effects of the burst remain visible in the rotational spectra for as long as 10 5 yr after the burst has ended, highlighting the importance of considering luminosity variations when analyzing molecular line observations in protostars. The spherical models are currently not accurate enough to derive robust timescales from single-dish observations. As follow-up work, we suggest that the models be calibrated against spatially resolved observations in order to identify the best tracers to be used for statistically significant source samples.

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Section: Abundance Profilesmentioning

confidence: 84%

Chemical tracers of episodic accretion in low-mass protostars

Visser

Bergin

Jørgensen

2015

A&A

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“…This selective freeze-out of major ice reservoirs can change the overall elemental [C]/[O] abundance ratio in the gas and thus the composition of the atmospheres of giant planets that are formed there 94 . The CO snowline has been imaged with ALMA through N 2 H + observations in the nearby TW Hya disk 233 . N 2 H + is enhanced when its main destroyer, CO, freezes out.…”

Section: Protoplanetary Disksmentioning

confidence: 99%

Astrochemistry of dust, ice and gas: introduction and overview

Dishoeck

Ewine²

2014

Faraday Discuss.

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136

102

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A brief introduction and overview of the astrochemistry of dust, ice and gas and their interplay is presented, aimed at non-specialists. The importance of basic chemical physics studies of critical reactions is illustrated through a number of recent examples. Such studies have also triggered new insight into chemistry, illustrating how astronomy and chemistry can enhance each other. Much of the chemistry in star- and planet-forming regions is now thought to be driven by gas-grain chemistry rather than pure gas-phase chemistry, and a critical discussion of the state of such models is given. Recent developments in studies of diffuse clouds and PDRs, cold dense clouds, hot cores, protoplanetary disks and exoplanetary atmospheres are summarized, both for simple and more complex molecules, with links to papers presented in this volume. In spite of many lingering uncertainties, the future of astrochemistry is bright: new observational facilities promise major advances in our understanding of the journey of gas, ice and dust from clouds to planets.Comment: Introductory paper for Faraday Discussions 168 conference, April 201

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“…through dust growth) but are also relevant for the final composition of bodies formed in the disk. Recently Qi et al (2013) reported the imaging of the CO snowline in the TW Hya disk via observations of the N 2 H + ion. N 2 H + is efficiently destroyed by proton transfer to CO…”

Section: Ice Linesmentioning

confidence: 99%

“…Surface chemistry processes produce complex molecules on the dust surface (e.g. hydrogenation of CO to form H 2 CO, Qi et al 2013), and these molecules may subsequently be photo-desorbed. One prominent example for this suggested formation process is methanol (Walsh et al 2010;Dutrey et al 2014).…”

Section: Chemical Structurementioning

confidence: 99%

The Gas Disk: Evolution and Chemistry

et al. 2016

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Protoplanetary disks are the birthplaces of planetary systems. The evolution of the star-disk system and the disk chemical composition determines the initial conditions for planet formation. Therefore a comprehensive understanding of the main physical and chemical processes in disks is crucial for our understanding of planet formation. We give an overview of the early evolution of disks, discuss the importance of the stellar high-energy radiation for disk evolution and describe the general thermal and chemical structure of disks. Finally we provide an overview of observational tracers of the gas component and disk winds.

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Imaging of the CO Snow Line in a Solar Nebula Analog

Cited by 302 publications

References 51 publications

Chemical tracers of episodic accretion in low-mass protostars

Chemical tracers of episodic accretion in low-mass protostars

Astrochemistry of dust, ice and gas: introduction and overview

The Gas Disk: Evolution and Chemistry

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