Resolving the Circumstellar Disk of Hl Tauri at Millimeter Wavelengths

Abstract

We present results of high-resolution imaging toward HL Tau by the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We have obtained λ = 1.3 mm and 2.7 mm dust continua with an angular resolution down to 0.13 ′′ . Through model fitting to the two wavelength data simultaneously in Bayesian inference using a flared viscous accretion disk model, we estimate the physical properties of HL Tau, such as density distribution, dust opacity spectral index, disk mass, disk size, inclination angle, position angle, and disk thickness. HL Tau has a circumstellar disk mass of 0.13 M ⊙ , a characteristic radius of 79 AU, an inclination of 40 • , and a position angle of 136 • . Although a thin disk model is preferred by our two wavelength data, a thick disk model is needed to explain the high mid-and far-infrared emission of the HL Tau spectral energy distribution. This could imply large dust grains settled down on the mid plane with fine dust grains mixed with gas. The HL Tau disk is likely gravitationally unstable and can be fragmented between 50 and 100 AU of radius. However, we did not detect dust thermal continuum supporting the protoplanet candidate claimed by a previous study using observations of the Very Large Array at λ = 1.3 cm.

Grain Size Constraints on Hl Tau With Polarization Signature

“…The opacity index is typically equal to or less than one in protoplanetary disks, which can be explained with millimeter-sized grains (e.g., Beckwith & Sargent 1991). In the case of HL Tau, the dust opacity index is in the range from 0.3 to 0.8 for the bright rings (Kwon et al 2011;ALMA Partnership et al 2015). Therefore, the maximum grain size of 150 μm, which is obtained in this paper, is not consistent with the constraints on the grain size with the opacity index if the emission is optically thin.…”

“…This young star is surrounded by an envelope and is producing jets and outflows, which indicates highly active star formation (e.g., Hayashi et al 1993). The millimeter emission from the envelope and the disk has been intensively investigated with interferometers (Beckwith et al 1990;Mundy et al 1996;Wilner et al 1996;Looney et al 2000;Greaves et al 2008;Kwon et al 2011). Furthermore, Atacama Large Millimeter/submillimeter Array (ALMA) has revealed that the circumstellar disk around HL Tau has multiple rings at submillimeter wavelengths, which might be a signature of multiple planets (ALMA Partnership et al 2015).…”

How do giant planetary cores shape the dust disk?

“…An infinitesimally thin disk around a star resembling the observed HL Tau system (Kwon et al 2011) is modelled. Thus, the vertically integrated versions of the hydrodynamical equations are solved in cylindrical coordinates (r, φ, z) centred on the star where the disk lies in the equatorial plane (z = 0).…”

“…where Σ 0 is the surface density at r = 1 such that the total disk mass is equal to 0.24 (0.13 M ) in order to match the value found by Kwon et al (2011). The disk is modelled with a locally isothermal equation of state, which keeps the initial temperature stratification constant throughout the whole simulation.…”

Velocity-Resolved Hot Water Emission Detected Toward Hl Tau With the Submillimeter Array

“…However, if the emission originates in a disk, the line profile should be symmetric unless something is hiding the redshifted counterpart. The disk inclination with respect to the line of sight is estimated to be ∼40° (Kwon et al 2011;ALMA Partnership et al 2015), so the redshifted counterpart should be visible. Even in the very inner disk where the dust is optically thick at sub-millimeter wavelengths (ALMA Partnership et al 2015), the surface layers of the entire disk are visible and not just the blueshifted side.…”