HL Tau Disk in HCO⁺ (3–2) and (1–0) with ALMA: Gas Density, Temperature, Gap, and One-arm Spiral

Abstract

We present our observational results of the 1.1 mm continuum and the HCO + (3-2) line in HL Tau at angular resolutions of 0. 1 obtained with ALMA and our data analysis of the 2.9 mm and 1.1 mm continuum and the HCO + (3-2) and (1-0) lines of the HL Tau disk. The Keplerian rotation of the HL Tau disk is well resolved in the HCO + (3-2) emission, and the stellar mass is estimated to be 2.1±0.2 M with a disk inclination angle of 47 • . The radial profiles of the HCO + column density and excitation temperature are measured with the LTE analysis of the two transitions of the HCO + emission. An HCO + gas gap at a radius of 30 au, where the column density drops by a factor of 4-8, is found in the HCO + column density profile, coincident with the dust gap traced by the continuum emission. No other clear HCO + gas gap is seen. This HCO + gas gap can be opened by a planet with mass of 0.5-0.8 M J , which is comparable to the planet mass adopted in numerical simulations to form the dust gap at the same radius in the HL Tau disk. In addition to the disk component, a one-arm spiral with a length of ∼3 (520 au) stretching out from the inner disk is observed in the HCO + (3-2) emission. The observed velocity structures along the spiral suggest an infalling and rotating gas stream toward the inner disk.

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT)

“…The systemic velocity is ∼ +7.0 km s −1 (in agreement with ALMA Partnership et al 2015;Wu et al 2018). The same rotating gradient has been observed using HCO + (ALMA Partnership et al 2015;Yen et al 2019), C 18 O (Wu et al 2018), and 13 C 17 O (Booth & Ilee 2020). Also the emission towards IRAS04302 disk shows a rotation pattern.…”

Herschel Observations of Protoplanetary Disks in Lynds 1641*

“…These include emission from an envelope/accretion streamer or outflow cavity, or perturbations by an unseen companion. This arc is similar to the streamer that is feeding material from the local environment onto Per-emb-2 (Pineda et al 2020), [BHB2007] 1 (Alves et al 2020), SU Aur (Ginski et al 2021), and, on a smaller scale, HL Tau (Yen et al 2019). However, what is unique about the emission around [MGM2012] 512 is that it is detected in the continuum.…”

13C17O suggests gravitational instability in the HL Tau disc

“…In our previous study of the HD 163296 disc we performed 2D radiative transfer models of multiple CO isotopologues and transitions using a well tested 2D physical structure (Booth et al 2019). Many molecular line observations toward HL Tau are significantly affected by absorption and complex velocity gradients from the surrounding cloud (see, e.g., ALMA Partnership et al 2015;Yen et al 2019), meaning a similar wealth of observational data is not readily available. We therefore employ a simpler method of analysis.…”