skip to main content

SciTech ConnectSciTech Connect

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

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 » and we propose that the inner region of TW Hya is a dust (and possibly planet) growth factory as predicted by previous theoretical work.« less
Authors:
; ;  [1] ; ;  [2]
  1. Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109 (United States)
  2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
Publication Date:
OSTI Identifier:
22364290
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 799; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
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