An enhanced cosmic-ray flux towards ζ Persei inferred from a laboratory study of the H3+–e- recombination rate

McCall, Benjamin J.; Huneycutt, A. J.; Saykally, Richard J.; Geballe, T. R.; Djurić, N.; Dunn, G. H.; Semaniak, J.; Novotny, Steffen; Al-Khalili, A.; Ehlerding, Anneli; Hellberg, F.; Kalhori, S.; Neau, A.; Thomas, Richard; Österdahl, Fabian; Larsson, Mats

doi:10.1038/nature01498

Cited by 328 publications

(343 citation statements)

References 29 publications

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“…The discovery of significant abundances of H + 3 in diffuse clouds (McCall et al 1998), confirmed by follow-up detections (Geballe et al 1999;McCall et al 2003;Indriolo et al 2007), has led to values of ζ H 2 larger by about one order of magnitude than both the "standard" rate and previous estimates based on the abundance of OH and HD in dense clouds. Given the relative simplicity of the chemistry of H + 3 , it is now believed that diffuse clouds are characterized by CR ionization rates ζ H 2 ≈ 2 × 10 −16 s −1 or larger.…”

Section: Introductionmentioning

confidence: 77%

“…This high value of ζ H 2 in the diffuse interstellar gas can be reconciled with the lower values measured in cloud cores and massive protostellar envelopes by invoking various mechanisms of CR screening in molecular clouds due to either self-generated Alfvén waves in the plasma (Skilling & Strong 1976;Hartquist et al 1978;Padoan & Scalo 2005) or to magnetic mirror effects (Cesarsky & Völk 1978;Chandran 2000). An alternative explanation, based on the possible existence of a low-energy flux of CR particles, is that they can penetrate (and ionize) diffuse clouds but not dense clouds, as recently proposed by McCall et al (2003), see also Takayanagi (1973) and Umebayashi & Nakano (1981). This latter scenario is explored quantitatively in the present paper.…”

Section: Introductionmentioning

confidence: 99%

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Cosmic-ray ionization of molecular clouds

Padovani¹,

Galli²,

Glassgold³

2009

A&A

354

490

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Context. Low-energy cosmic rays are a fundamental source of ionization for molecular clouds, influencing their chemical, thermal, and dynamical evolution. Aims. The purpose of this work is to explore the possibility that a low-energy component of cosmic rays, not directly measurable from the Earth, can account for the discrepancy between the ionization rate measured in diffuse and dense interstellar clouds. Methods. We collected the most recent experimental and theoretical data on the cross sections for the production of H + 2 and He + by electron and proton impact and discuss the available constraints on the cosmic-ray fluxes in the local interstellar medium. Starting from different extrapolations at low energies of the demodulated cosmic-ray proton and electron spectra, we computed the propagated spectra in molecular clouds in the continuous slowing-down approximation taking all the relevant energy loss processes into account. Results. The theoretical value of the cosmic-ray ionization rate as a function of the column density of traversed matter agrees with the observational data only if the flux of either cosmic-ray electrons or of protons increases at low energies. The most successful models are characterized by a significant (or even dominant) contribution of the electron component to the ionization rate, in agreement with previous suggestions. However, the large spread of cosmic-ray ionization rates inferred from chemical models of molecular cloud cores remains to be explained. Conclusions. Available data combined with simple propagation models support the existence of a low-energy component (below ∼100 MeV) of cosmic-ray electrons or protons responsible for the ionization of molecular cloud cores and dense protostellar envelopes.

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Section: Introductionmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Cosmic-ray ionization of molecular clouds

Padovani¹,

Galli²,

Glassgold³

2009

A&A

354

490

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“…Rate coefficients in 10-30 K gas are typically 10 −7 to 10 −6 cm 3 s −1 . The dissociative recombination of H + 3 , a key species in the chemistry, has been subject to considerable discussion in the last three decades, but experiments appear to converge on a rapid value of ∼ 10 −6 cm 3 s −1 at low temperatures 121 .…”

Section: Destructionmentioning

confidence: 99%

Astrochemistry of dust, ice and gas: introduction and overview

Dishoeck

Ewine²

2014

Faraday Discuss.

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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“…Spectroscopy of H + 3 at 3.5 µm toward a local diffuse cloud (McCall et al 2003) indicates a local enhancement of ζ CR relative to the above value by about a factor of 10, taking the distribution of species along the line of sight into account (Le Petit et al 2004). On the other hand, observations of emission lines of DCO + and other ions toward highly shielded pre-stellar cores indicate 8…”

Section: Cosmic-ray Ionizationmentioning

confidence: 99%

The chemistry of high-mass star formation

Tak¹,

Floris²

2005

Proc. IAU

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Abstract. This paper reviews the chemistry of star-forming regions, with an emphasis on the formation of high-mass stars. We first outline the basic molecular processes in dense clouds, their implementation in chemical models, and techniques to measure molecular abundances. Then, recent observational, theoretical and laboratory developments are reviewed on the subjects of hot molecular cores, cosmic-ray ionization, depletion and deuteration, and oxygen chemistry. The paper concludes with a summary of outstanding problems and future opportunities.

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An enhanced cosmic-ray flux towards ζ Persei inferred from a laboratory study of the H3+–e- recombination rate

Cited by 328 publications

References 29 publications

Cosmic-ray ionization of molecular clouds

Cosmic-ray ionization of molecular clouds

Astrochemistry of dust, ice and gas: introduction and overview

The chemistry of high-mass star formation

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