High Spatial Resolution Observations of Molecular Lines toward the Protoplanetary Disk around TW Hya with ALMA

Hideko Nomura, Takashi Tsukagoshi, Ryohei Kawabe, Takayuki Muto, Kazuhiro D. Kanagawa, Yuri Aikawa, Eiji Akiyama, Satoshi Okuzumi, Shigeru Ida, Seokho Lee, Catherine Walsh, T. J. Millar

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We present molecular line observations of 13CO and C18O J = 3 - 2, CN N = 3 - 2, and CS J = 7 - 6 lines in the protoplanetary disk around TW Hya at a high spatial resolution of ∼9 au (angular resolution of 0.″15), using the Atacama Large Millimeter/Submillimeter Array. A possible gas gap is found in the deprojected radial intensity profile of the integrated C18O line around a disk radius of ∼58 au, slightly beyond the location of the au-scale dust clump at ∼52 au, which resembles predictions from hydrodynamic simulations of planet-disk interaction. In addition, we construct models for the physical and chemical structure of the TW Hya disk, taking account of the dust surface density profile obtained from high spatial resolution dust continuum observations. As a result, the observed flat radial profile of the CN line intensities is reproduced due to a high dust-to-gas surface density ratio inside ∼20 au. Meanwhile, the CO isotopologue line intensities trace high temperature gas and increase rapidly inside a disk radius of ∼30 au. A model with either CO gas depletion or depletion of gas-phase oxygen elemental abundance is required to reproduce the relatively weak CO isotopologue line intensities observed in the outer disk, consistent with previous atomic and molecular line observations toward the TW Hya disk. Further observations of line emission of carbon-bearing species, such as atomic carbon and HCN, with high spatial resolution would help to better constrain the distribution of elemental carbon abundance in the disk gas.

Original languageEnglish
Article number113
Number of pages10
JournalThe Astrophysical Journal
Issue number2
Publication statusPublished - 22 Jun 2021

Bibliographical note

22 pages, 7 figures, Accepted for publication in ApJ


  • astro-ph.EP

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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