GG Tauri A: gas properties and dynamics from the cavity to the outer disk

Abstract

Context. GG Tau A is the prototype of a young triple T Tauri star that is surrounded by a massive and extended Keplerian outer disk. The central cavity is not devoid of gas and dust and at least GG Tau Aa exhibits its own disk of gas and dust emitting at millimeter wavelengths. Its observed properties make this source an ideal laboratory for investigating planet formation in young multiple solartype stars. Aims. We used new ALMA 13 CO and C 18 O(3-2) observations obtained at high angular resolution (∼ 0.2 ) together with previous CO(3-2) and (6-5) ALMA data and continuum maps at 1.3 and 0.8 mm in order to determine the gas properties (temperature, density, and kinematics) in the cavity and to a lesser extent in the outer disk. Methods. By deprojecting, we studied the radial and azimuthal gas distribution and its kinematics. We also applied a new method to improve the deconvolution of the CO data and in particular better quantify the emission from gas inside the cavity. We perform local and nonlocal thermodynamic equilibrium studies in order to determine the excitation conditions and relevant physical parameters inside the ring and in the central cavity.Results. Residual emission after removing a smooth-disk model indicates unresolved structures at our angular resolution, probably in the form of irregular rings or spirals. The outer disk is cold, with a temperature < 20 K beyond 250 au that drops quickly (∝ r −1 ). The kinematics of the gas inside the cavity reveals infall motions at about 10% of the Keplerian speed. We derive the amount of gas in the cavity, and find that the brightest clumps, which contain about 10% of this mass, have kinetic temperatures 40 − 80 K, CO column densities of a few 10 17 cm −2 , and H 2 densities around 10 7 cm −3 . Conclusions. Although the gas in the cavity is only a small fraction of the disk mass, the mass accretion rate throughout the cavity is comparable to or higher than the stellar accretion rate. It is accordingly sufficient to sustain the circumstellar disks on a long timescale.

Gap, shadows, spirals, and streamers: SPHERE observations of binary-disk interactions in GG Tauri A

“…Right: polarized intensity image with ALMA Band 7 (0.9 mm) continuum contours overplotted (blue). The ALMA observations were published in Phuong et al (2020a). The ALMA image was registered such that the inner continuum emission, attributed to a circumstellar disk around Aa, coincides with the NIR position of Aa.…”

“…The circumbinary disk around GG Tau A is observed as a large and massive disk with a cleared cavity. While the gaseous disk extends out to more than ∼850 au and reveals a reduced amount of gas in the inner region (e.g., Guilloteau et al 1999;Dutrey et al 2014;Phuong et al 2020a), the population of large dust grains observed at (sub-)millimeter wavelengths is confined within a narrow ring surrounding a deeply depleted dust cavity, spanning a full width of ∼60-80 au centered at a radial distance of about 250 au with respect to the system barycenter (e.g., Andrews et al 2014;Dutrey et al 2014;Tang et al 2016). Scattered-light observations in the optical, near-and thermal infrared regime infer that the inner edge of the outer disk of the small-grain population is located at about ∼190-200 au (e.g., Krist et al 2002;Duchêne et al 2004;Itoh et al 2014;Yang et al 2017).…”

An unbiased NOEMA 2.6 to 4 mm survey of the GG Tau ring: First detection of CCS in a protoplanetary disk

“…The data were compared in the uv-plane with visibilities predicted for a disk model using the radiative transfer code DiskFit (Piétu et al 2007). A description of DiskFit usage for GG Tau can be found in the appendix of Phuong et al (2020).…”

“…D = detected, U = undetected, and M = marginal detected T 0 = 15 K for S-bearing species, and T 0 = 25 K for all other molecules. ( * ) The values are taken from Phuong et al (2020).…”

“…Beyond the ring, the outer gas disk extends out to ∼800 au. The temperature profile of the disk has been studied by Dutrey et al (2014a), Guilloteau et al (1999), andPhuong et al (2020): the dust temperature is 14 K at 200 au, and the kinetic temperature derived from CO analysis is ∼25 K at the same radius. The large size, low temperature, and large mass make GG Tau A disk an ideal laboratory to study cold molecular chemistry.…”