High resolution observations of molecular emission lines toward the CI Tau proto-planetary disc: planet-carved gaps or shadowing?

Abstract

Recent observations have revealed that most proto-planetary discs show a pattern of bright rings and dark gaps. However, most of the high-resolution observations have focused only on the continuum emission. In this Paper we present high-resolution ALMA band 7 (0.89mm) observations of the disc around the star CI Tau in the ${}^{12}$CO & ${}^{13}$CO $J=3$-2 and CS $J=7$-6 emission lines. Our recent work demonstrated that the disc around CI Tau contains three gaps and rings in continuum emission, and we look for their counterparts in the gas emission. While we find no counterpart of the third gap and ring in ${}^{13}$CO, the disc has a gap in emission at the location of the second continuum ring (rather than gap). We demonstrate that this is mostly an artefact of the continuum subtraction, although a residual gap still remains after accounting for this effect. Through radiative transfer modelling we propose this is due to the inner disc shadowing the outer parts of the disc and making them colder. This raises a note of caution in mapping high-resolution gas emission lines observations to the gas surface density - while possible, this needs to be done carefully. In contrast to ${}^{13}$CO, CS emission shows instead a ring morphology, most likely due to chemical effects. Finally, we note that ${}^{12}$CO is heavily absorbed by the foreground preventing any morphological study using this line.

17 pages, 17 figures; accepted for publication in MNRAS

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Cited by in corpus (10)

• Molecules with ALMA at Planet-forming Scales (MAPS) I: Program Overview and Highlights
• Molecules with ALMA at Planet-forming Scales (MAPS) V: CO gas distributions
• Efficient planet formation by pebble accretion in ALMA rings
• Mapping Protoplanetary Disk Vertical Structure with CO Isotopologue Line Emission
• exoALMA. XVII. Characterizing the Gas Dynamics around Dust Asymmetries
• Self-consistent ring model in protoplanetary disks: temperature dips and substructure formation
• Molecules with ALMA at Planet-forming Scales (MAPS) III: Characteristics of Radial Chemical Substructures
• Molecules with ALMA at Planet-forming Scales (MAPS). XV. Tracing protoplanetary disk structure within 20 au
• High-contrast Imaging around a 2 Myr-old CI Tau with a Close-in Gas Giant
• CO Line Emission Surfaces and Vertical Structure in Mid-Inclination Protoplanetary Disks