Gas Gaps in the Protoplanetary Disk Around the Young Protostar Hl Tau

Abstract

Aims. The protoplanetary disk around HL Tau is so far the youngest candidate of planet formation, and it is still embedded in a protostellar envelope with a size of thousands of au. In this work, we study the gas kinematics in the envelope and its possible influence on the embedded disk. Methods. We present our new ALMA cycle 3 observational results of HL Tau in the 13 CO (2-1) and C 18 O (2-1) emission at resolutions of 0 ′′. 8 (110 au), and we compare the observed velocity pattern with models of different kinds of gas motions. Results. Both the 13 CO and C 18 O emission lines show a central compact component with a size of 2 ′′ (280 au), which traces the protoplanetary disk. The disk is clearly resolved and shows a Keplerian motion, from which the protostellar mass of HL Tau is estimated to be 1.8±0.3 M ⊙ , assuming the inclination angle of the disk to be 47 • from the plane of the sky. The 13 CO emission shows two arc structures with sizes of 1000-2000 au and masses of 3 × 10 −3 M ⊙ connected to the central disk. One is blueshifted and stretches from the northeast to the northwest, and the other is redshifted and stretches from the southwest to the southeast. We find that simple kinematical models of infalling and (counter-)rotating flattened envelopes cannot fully explain the observed velocity patterns in the arc structures. The gas kinematics of the arc structures can be better explained with three-dimensional infalling or outflowing motions. Nevertheless, the observed velocity in the northwestern part of the blueshifted arc structure is ∼60-70% higher than the expected free-fall velocity. We discuss two possible origins of the arc structures: (1) infalling flows externally compressed by an expanding shell driven by XZ Tau and (2) outflowing gas clumps caused by gravitational instabilities in the protoplanetary disk around HL Tau.

What is the Mass of a Gap-opening Planet?

“…Rich structures have been identified in disk images in near infrared (NIR) and in mm/cm dust continuum and gas emission. Among them, a particularly intriguing class of features is narrow gaps, found in systems such as TW Hya (Debes et al 2013;Rapson et al 2015b;Akiyama et al 2015;Andrews et al 2016), HD 169142 (Quanz et al 2013;Momose et al 2015), HD 97048 (Ginski et al 2016;Walsh et al 2016;van der Plas et al 2016), AB Aur (Hashimoto et al 2011), V 4046 Sgr (Rapson et al 2015a), HD 141569 (Weinberger et al 1999;Mouillet et al 2001;Konishi et al 2016;Perrot et al 2016), RX J1615.3-3255 (de Boer et al 2016, and HL Tau (ALMA Partnership et al 2015;Yen et al 2016;Carrasco-González et al 2016). These gaps have both their inner and outer edges revealed in images, enabling a full view of the gap structure and particularly, a measurement of the gap width.…”

1000 au exterior arcs connected to the protoplanetary disk around HL Tauri

“…08 (262±17 au × 179±11 au). The gas kinematic temperature in the protoplanetary disk around HL Tau was estimated to be 60 K at the outer radii of 60-100 au from the ALMA observations in the CO (1-0) emission (Yen et al 2016 of 1.5 × 10 −7 relative to H 2 (Brittain et al 2005;Smith et al 2015). If the excitation temperature is assumed to be 100 K (Brittain et al 2005), the estimated mass becomes 5 × 10 −3 M ⊙ .…”

Pebble accretion in Class 0/I YSOs as a possible pathway for early planet formation

“…One of the most intriguing objects among these is HL Tau, the circumstellar disk whose several axisymmetric sharp gaps and rings have been imaged (ALMA Partnership et al 2015). In addition, the HCO + observation obtained by ALMA also suggests the existence of a gap structure in the gas component (Yen et al 2016). Many mechanisms have been suggested to reproduce the gap and ring structures found around HL Tau and other objects; for example, magnetorotational instability (Johansen et al 2009;Uribe et al 2011), secular gravitational instability (Youdin 2011;Takahashi & Inutsuka 2014Tominaga et al 2018), baroclinic instability (Kretke & Lin 2007;Dzyurkevich et al 2010;Flock et al 2015), dust sintering , and photoevaporation (Ercolano et al 2017).…”