CONSTRAINING THE X-RAY AND COSMIC-RAY IONIZATION CHEMISTRY OF THE TW Hya PROTOPLANETARY DISK: EVIDENCE FOR A SUB-INTERSTELLAR COSMIC-RAY RATE

Cleeves, L. Ilsedore; Bergin, Edwin A.; Adams, Fred C.; Qi, Chunhua; Öberg, Karin I.

doi:10.1088/0004-637X/799/2/204

Title: CONSTRAINING THE X-RAY AND COSMIC-RAY IONIZATION CHEMISTRY OF THE TW Hya PROTOPLANETARY DISK: EVIDENCE FOR A SUB-INTERSTELLAR COSMIC-RAY RATE

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Abstract

We present an observational and theoretical study of the primary ionizing agents (cosmic rays (CRs) and X-rays) in the TW Hya protoplanetary disk. We use a set of resolved and unresolved observations of molecular ions and other molecular species, encompassing 11 lines total, in concert with a grid of disk chemistry models. The molecular ion constraints comprise new data from the Submillimeter Array on HCO{sup +}, acquired at unprecedented spatial resolution, and data from the literature, including ALMA observations of N{sub 2}H{sup +}. We vary the model incident CR flux and stellar X-ray spectra and find that TW Hya's HCO{sup +} and N{sub 2}H{sup +} emission are best-fit by a moderately hard X-ray spectra, as would be expected during the ''flaring'' state of the star, and a low CR ionization rate, ζ{sub CR} ≲ 10{sup –19} s{sup –1}. This low CR rate is the first indication of the presence of CR exclusion by winds and/or magnetic fields in an actively accreting T Tauri disk system. With this new constraint, our best-fit ionization structure predicts a low turbulence ''dead-zone'' extending from the inner edge of the disk out to 50-65 AU. This region coincides with an observed concentration of millimeter grains,more »« less

Authors:

Cleeves, L. Ilsedore; Bergin, Edwin A.; Adams, Fred C. ^[1]; Qi, Chunhua; Öberg, Karin I. ^[2]

Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109 (United States)
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

Publication Date:: Sun Feb 01 00:00:00 EST 2015

OSTI Identifier:: 22364290

Resource Type:: Journal Article

Journal Name:: Astrophysical Journal

Additional Journal Information:: Journal Volume: 799; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X

Country of Publication:: United States

Language:: English

Subject:: 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; CONCENTRATION RATIO; COSMIC DUST; COSMIC RADIATION; HARD X RADIATION; IONIZATION; LIMITING VALUES; MAGNETIC FIELDS; MOLECULAR IONS; PLANETS; PROTOPLANETS; SPATIAL RESOLUTION; STARS; STELLAR WINDS; TURBULENCE; X-RAY SPECTRA

Citation Formats


                    Cleeves, L. Ilsedore, Bergin, Edwin A., Adams, Fred C., Qi, Chunhua, and Öberg, Karin I. CONSTRAINING THE X-RAY AND COSMIC-RAY IONIZATION CHEMISTRY OF THE TW Hya PROTOPLANETARY DISK: EVIDENCE FOR A SUB-INTERSTELLAR COSMIC-RAY RATE.  United States: N. p., 2015. 
        Web.  doi:10.1088/0004-637X/799/2/204.

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                    Cleeves, L. Ilsedore, Bergin, Edwin A., Adams, Fred C., Qi, Chunhua, & Öberg, Karin I. CONSTRAINING THE X-RAY AND COSMIC-RAY IONIZATION CHEMISTRY OF THE TW Hya PROTOPLANETARY DISK: EVIDENCE FOR A SUB-INTERSTELLAR COSMIC-RAY RATE.  United States.  https://doi.org/10.1088/0004-637X/799/2/204

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                    Cleeves, L. Ilsedore, Bergin, Edwin A., Adams, Fred C., Qi, Chunhua, and Öberg, Karin I. 2015.  
        "CONSTRAINING THE X-RAY AND COSMIC-RAY IONIZATION CHEMISTRY OF THE TW Hya PROTOPLANETARY DISK: EVIDENCE FOR A SUB-INTERSTELLAR COSMIC-RAY RATE".  United States.  https://doi.org/10.1088/0004-637X/799/2/204.

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@article{osti_22364290,

  title        = {CONSTRAINING THE X-RAY AND COSMIC-RAY IONIZATION CHEMISTRY OF THE TW Hya PROTOPLANETARY DISK: EVIDENCE FOR A SUB-INTERSTELLAR COSMIC-RAY RATE},

  author       = {Cleeves, L. Ilsedore and Bergin, Edwin A. and Adams, Fred C. and Qi, Chunhua and Öberg, Karin I.},

  abstractNote = {We present an observational and theoretical study of the primary ionizing agents (cosmic rays (CRs) and X-rays) in the TW Hya protoplanetary disk. We use a set of resolved and unresolved observations of molecular ions and other molecular species, encompassing 11 lines total, in concert with a grid of disk chemistry models. The molecular ion constraints comprise new data from the Submillimeter Array on HCO{sup +}, acquired at unprecedented spatial resolution, and data from the literature, including ALMA observations of N{sub 2}H{sup +}. We vary the model incident CR flux and stellar X-ray spectra and find that TW Hya's HCO{sup +} and N{sub 2}H{sup +} emission are best-fit by a moderately hard X-ray spectra, as would be expected during the ''flaring'' state of the star, and a low CR ionization rate, ζ{sub CR} ≲ 10{sup –19} s{sup –1}. This low CR rate is the first indication of the presence of CR exclusion by winds and/or magnetic fields in an actively accreting T Tauri disk system. With this new constraint, our best-fit ionization structure predicts a low turbulence ''dead-zone'' extending from the inner edge of the disk out to 50-65 AU. This region coincides with an observed concentration of millimeter grains, and we propose that the inner region of TW Hya is a dust (and possibly planet) growth factory as predicted by previous theoretical work.},

  doi          = {10.1088/0004-637X/799/2/204},

  url          = {https://www.osti.gov/biblio/22364290},
  journal      = {Astrophysical Journal},

  issn         = {0004-637X},

  number       = 2,

  volume       = 799,

  place        = {United States},

  year         = {Sun Feb 01 00:00:00 EST 2015},

  month        = {Sun Feb 01 00:00:00 EST 2015}

}

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