Transition From the Infalling Envelope to the Keplerian Disk Around L1551 Irs 5

Abstract

We present combined SubMillimeter Array (SMA) + Atacama Submillimeter Telescope Experiment (ASTE) images of the Class I protobinary L1551 IRS 5 in the CS (J = 7-6) line, the submillimeter images of L1551 IRS 5 with the most complete spatial sampling ever achieved (0. 9 -36 ). The SMA image of L1551 IRS 5 in the 343 GHz dust-continuum emission is also presented, which shows an elongated feature along the northwest to southeast direction (∼160 AU × 80 AU), perpendicular to the associated radio jets. The combined SMA+ASTE images show that the high-velocity ( 1.5 km s −1 ) CS emission traces the structure of the dust component and shows a velocity gradient along the major axis, which is reproduced by a geometrically-thin Keplerian-disk model with a central stellar mass of ∼0.5 M . The low-velocity ( 1.3 km s −1 ) CS emission shows an extended (∼1000 AU) feature that exhibits slight south (blueshifted) to north (redshifted) emission offsets, which is modeled with a rotating and infalling envelope with a conserved angular momentum. The rotational motion of the envelope connects smoothly to the inner Keplerian rotation at a radius of ∼64 AU. The infalling velocity of the envelope is ∼three times lower than the free-fall velocity toward the central stellar mass of 0.5 M . These results demonstrate transition from the infalling envelope to the Keplerian disk, consistent with the latest theoretical studies of disk formation. We suggest that sizable (r ∼50-200 AU) Keplerian disks are already formed when the protostars are still deeply embedded in the envelopes.

On the accretion process in a high-mass star forming region

“…Models considering a protostardisk system (e.g., Yorke & Sonnhalter 2002;Krumholz et al 2005;Banerjee & Pudritz 2007;Tan & McKee 2002;McKee & Tan 2003;Bonnell & Bate 2006;Padoan et al 2014) suggest how the accretion of matter can overcome radiative pressure. Evidence of such accretion has been observed toward low-mass star formation cores (e.g., Chou et al 2014), but similar observational evidence is still scarce toward high-mass star forming regions. Not only are MYSOs typically observed at large distances, have high extinction, and form in clusters, but they also have relatively short time scales on their evolutionary phases because high far-UV and extreme UV fluxes photo evaporate the disk on time scales of ∼10 5 yrs.…”

Rotationally Driven Fragmentation in the Formation of the Binary Protostellar System L1551 Irs 5

“…In a manner analogous to the circumstellar disks, the smallest nonintersecting orbit in the circumbinary disk defines the innermost stable orbit and hence the minimum size of a central cavity. In Figure 5(a), no central depression, let alone cavity, is evident in the image of the dust emission (or indeed in images of molecular-gas emission as presented by Chou et al 2014). At an angular resolution of 0 80×0 52 in Figure 5(a), however, emission from the circumstellar disks cannot be separated from that of the circumbinary disk.…”

“…L1551 IRS 5 resides at the center of a flattened, rotating, and infalling envelope of dust and molecular gas (Momose et al 1998;Takakuwa et al 2004;Chou et al 2014). In C 18 O (Momose et al 1998), the centrally condensed portion of the envelope has a size of 2380×1050 au as measured at the 3σ level, and a position angle for its major axis of 162°.…”

“…In CS(7-6) (Chou et al 2014), the envelope is inferred to transition to a rotationally supported circumbinary disk (i.e., exhibiting Keplerian motion) at a radius of ∼0 46 (a projected radius of ∼64 au). From a Keplerian fit to the spatial-kinematic structure of the circumbinary disk (assuming a geometrically thin disk), Chou et al (2014) infer an inclination of ∼60°for this disk and a position angle of ∼147°for its major axis. Both the inclination and position angle for the major axis of the envelope are therefore closely comparable (within ∼15°) to the corresponding parameters for the two circumstellar disks (Table 2).…”

Cometary ices in forming protoplanetary disc midplanes

“…Observational evidence for them is scarce, because high spatial resolution ( 30 AU) is necessary to get spatial information for a small (∼ 100 AU) target,whose emission is easily overwhelmed by that of the more massive envelope, making it hard to constrain their physical parameters. Only recently, observations have shown embedded Keplerian discs of ∼ 50 − 300 AU in radius in embedded protostars (Tobin et al 2012(Tobin et al , 2013(Tobin et al , 2015Brinch & Jørgensen 2013;Murillo et al 2013;Sakai et al 2014;Harsono et al 2014;Chou et al 2014). Instead, significant modelling effort has focused on discs in the Class II/III stages of star formation (see, e.g., and table 1 in Woitke et al 2016 and the references therein).…”