Abstract
Complex organic molecules (COMs) in protoplanetary disks are key to understanding the origin of volatiles in comets in our solar system, yet the chemistry of COMs in protoplanetary disks ...remains poorly understood. Here, we present Atacama Large Millimeter/submillimeter Array Band 3 observations of the disk around the young outbursting star V883 Ori, where the COMs sublimate from ices and are thus observable thanks to the warm condition of the disk. We have robustly identified ten oxygen-bearing COMs including
13
C isotopologues in the disk-integrated spectra. The radial distributions of the COM emission, revealed by the detailed analyses of the line profiles, show the inner emission cavity, similar to the previous observations in Band 6 and Band 7. We found that the COMs abundance ratios with respect to methanol are significantly higher than those in the warm protostellar envelopes of IRAS 16293-2422 and similar to the ratios in the solar system comet 67P/Churyumov-Gerasimenko, suggesting the efficient (re)formation of COMs in protoplanetary disks. We also constrained the
12
C/
13
C and D/H ratios of COMs in protoplanetary disks for the first time. The
12
C/
13
C ratios of acetaldehyde, methyl formate, and dimethyl ether are consistently lower (∼20–30) than the canonical ratio in the interstellar medium (∼69), indicating the efficient
13
C-fractionation of CO. The D/H ratios of methyl formate are slightly lower than the values in IRAS 16293-2422, possibly pointing to the destruction and reformation of COMs in disks. We also discuss the implications for nitrogen and sulfur chemistry in protoplanetary disks.
Abstract
We present an overview of the Large Program, “Early Planet Formation in Embedded Disks (eDisk),” conducted with the Atacama Large Millimeter/submillimeter Array (ALMA). The ubiquitous ...detections of substructures, particularly rings and gaps, in protoplanetary disks around T Tauri stars raise the possibility that at least some planet formation may have already started during the embedded stages of star formation. In order to address exactly how and when planet formation is initiated, the program focuses on searching for substructures in disks around 12 Class 0 and 7 Class I protostars in nearby (<200 pc) star-forming regions through 1.3 mm continuum observations at a resolution of ∼7 au (0.″04). The initial results show that the continuum emission, mostly arising from dust disks around the sample protostars, has relatively few distinctive substructures, such as rings and spirals, in marked contrast to Class II disks. The dramatic difference may suggest that substructures quickly develop in disks when the systems evolve from protostars to Class II sources, or alternatively that high optical depth of the continuum emission could obscure internal structures. Kinematic information obtained through CO isotopologue lines and other lines reveals the presence of Keplerian disks around protostars, providing us with crucial physical parameters, in particular, the dynamical mass of the central protostars. We describe the background of the eDisk program, the sample selection and their ALMA observations, and the data reduction, and we also highlight representative first-look results.
Abstract
While dust disks around optically visible, Class II protostars are found to be vertically thin, when and how dust settles to the midplane are unclear. As part of the Atacama Large ...Millimeter/submillimeter Array large program, Early Planet Formation in Embedded Disks, we analyze the edge-on, embedded, Class I protostar IRAS 04302+2247, also nicknamed the “Butterfly Star.” With a resolution of 0.″05 (8 au), the 1.3 mm continuum shows an asymmetry along the minor axis that is evidence of an optically thick and geometrically thick disk viewed nearly edge-on. There is no evidence of rings and gaps, which could be due to the lack of radial substructure or the highly inclined and optically thick view. With 0.″1 (16 au) resolution, we resolve the 2D snow surfaces, i.e., the boundary region between freeze-out and sublimation, for
12
CO
J
= 2–1,
13
CO
J
= 2–1, C
18
O
J
= 2–1,
H
2
CO
J
= 3
0,3
–2
0,2
, and SO
J
= 6
5
–5
4
, and constrain the CO midplane snow line to ∼130 au. We find Keplerian rotation around a protostar of 1.6 ± 0.4
M
⊙
using C
18
O. Through forward ray-tracing using RADMC-3D, we find that the dust scale height is ∼6 au at a radius of 100 au from the central star and is comparable to the gas pressure scale height. The results suggest that the dust of this Class I source has yet to vertically settle significantly.
The chemical evolution of nitrogen during star and planet formation is still not fully understood. Ammonia (NH3) is a key specie in the understanding of the molecular evolution in star-forming clouds ...and nitrogen isotope fractionation. In this paper, we present high-spatial-resolution observations of multiple emission lines of NH3 toward the protobinary system NGC1333 IRAS4A with the Karl G. Jansky Very Large Array. We spatially resolved the binary (hereafter, 4A1 and 4A2) and detected compact emission of NH3 transitions with high excitation energies (≳100 K) from the vicinity of the protostars, indicating the NH3 ice has sublimated at the inner hot region. The NH3 column density is estimated to be ∼1017–1018 cm−2. We also detected two NH2D transitions, allowing us to constrain the deuterium fractionation of ammonia. The NH2D/NH3 ratios are as high as ∼0.3–1 in both 4A1 and 4A2. From comparisons with the astrochemical models in the literature, the high NH2D/NH3 ratios suggest that the formation of NH3 ices mainly started in the prestellar phase after the formation of bulk water ice finished, and that the primary nitrogen reservoir in the star-forming cloud could be atomic nitrogen (or N atoms) rather than nitrogen-bearing species such as N2 and NH3. The implications on the physical properties of IRAS4A’s cores are discussed as well.
Abstract
We present observations of the Class 0 protostar IRAS 16544–1604 in CB 68 from the “Early Planet Formation in Embedded Disks (eDisk)” ALMA Large program. The ALMA observations target ...continuum and lines at 1.3 mm with an angular resolution of ∼5 au. The continuum image reveals a dusty protostellar disk with a radius of ∼30 au seen close to edge-on and asymmetric structures along both the major and minor axes. While the asymmetry along the minor axis can be interpreted as the effect of the dust flaring, the asymmetry along the major axis comes from a real nonaxisymmetric structure. The C
18
O image cubes clearly show the gas in the disk that follows a Keplerian rotation pattern around a ∼0.14
M
⊙
central protostar. Furthermore, there are ∼1500 au scale streamer-like features of gas connecting from northeast, north–northwest, and northwest to the disk, as well as the bending outflow as seen in the
12
CO (2–1) emission. At the apparent landing point of the NE streamer, there is SO (6
5
–5
4
) and SiO (5–4) emission detected. The spatial and velocity structure of the NE streamer can be interpreted as a free-falling gas with a conserved specific angular momentum, and the detection of the SO and SiO emission at the tip of the streamer implies the presence of accretion shocks. Our eDisk observations have unveiled that the Class 0 protostar in CB 68 has a Keplerian-rotating disk with a flaring and nonaxisymmetric structure associated with accretion streamers and outflows.
Abstract
Constraining the physical and chemical structure of young embedded disks is crucial for understanding the earliest stages of planet formation. As part of the Early Planet Formation in ...Embedded Disks Atacama Large Millimeter/submillimeter Array Large Program, we present high spatial resolution (∼0.″1 or ∼15 au) observations of the 1.3 mm continuum and
13
CO
J
= 2–1, C
18
O
J
= 2–1, and SO
J
N
= 6
5
–5
4
molecular lines toward the disk around the Class I protostar L1489 IRS. The continuum emission shows a ring-like structure at 56 au from the central protostar and tenuous, optically thin emission extending beyond ∼300 au. The
13
CO emission traces the warm disk surface, while the C
18
O emission originates from near the disk midplane. The coincidence of the radial emission peak of C
18
O with the dust ring may indicate a gap-ring structure in the gaseous disk as well. The SO emission shows a highly complex distribution, including a compact, prominent component at ≲30 au, which is likely to originate from thermally sublimated SO molecules. The compact SO emission also shows a velocity gradient along a direction tilted slightly (∼15°) with respect to the major axis of the dust disk, which we interpret as an inner warped disk in addition to the warp around ∼200 au suggested by previous work. These warped structures may be formed by a planet or companion with an inclined orbit, or by a gradual change in the angular momentum axis during gas infall.
Abstract
Protostellar disks are an ubiquitous part of the star formation process and the future sites of planet formation. As part of the Early Planet Formation in Embedded Disks large program, we ...present high angular resolution dust continuum (∼40 mas) and molecular line (∼150 mas) observations of the Class 0 protostar IRAS 15398–3359. The dust continuum is small, compact, and centrally peaked, while more extended dust structures are found in the outflow directions. We perform a 2D Gaussian fitting and find the deconvolved size and 2
σ
radius of the dust disk to be 4.5 × 2.8 au and 3.8 au, respectively. We estimate the gas+dust disk mass assuming optically thin continuum emission to be 0.6
M
J
–1.8
M
J
, indicating a very low mass disk. The CO isotopologues trace components of the outflows and inner envelope, while SO traces a compact, rotating disk-like component. Using several rotation curve fittings on the position–velocity diagram of the SO emission, the lower limits of the protostellar mass and gas disk radius are 0.022
M
⊙
and 31.2 au, respectively, from our Modified 2 single power-law fitting. A conservative upper limit of the protostellar mass is inferred to be 0.1
M
⊙
. The protostellar mass accretion rate and the specific angular momentum at the protostellar disk edge are found to be in the range of (1.3–6.1) × 10
−6
M
⊙
yr
−1
and (1.2–3.8) × 10
−4
km s
−1
pc, respectively, with an age estimated between 0.4 × 10
4
yr and 7.5 × 10
4
yr. At this young age with no clear substructures in the disk, planet formation would likely not yet have started. This study highlights the importance of high-resolution observations and systematic fitting procedures when deriving dynamical properties of deeply embedded Class 0 protostars.
Abstract
We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Class I source Oph IRS 63 in the context of the Early Planet Formation in Embedded Disks large program. Our ...ALMA observations of Oph IRS 63 show a myriad of protostellar features, such as a shell-like bipolar outflow (in
12
CO), an extended rotating envelope structure (in
13
CO), a streamer connecting the envelope to the disk (in C
18
O), and several small-scale spiral structures seen toward the edge of the dust continuum (in SO). By analyzing the velocity pattern of
13
CO and C
18
O, we measure a protostellar mass of
M
⋆
= 0.5 ± 0.2
M
⊙
and confirm the presence of a disk rotating at almost Keplerian velocity that extends up to ∼260 au. These calculations also show that the gaseous disk is about four times larger than the dust disk, which could indicate dust evolution and radial drift. Furthermore, we model the C
18
O streamer and SO spiral structures as features originating from an infalling rotating structure that continuously feeds the young protostellar disk. We compute an envelope-to-disk mass infall rate of ∼10
−6
M
⊙
yr
−1
and compare it to the disk-to-star mass accretion rate of ∼10
−8
M
⊙
yr
−1
, from which we infer that the protostellar disk is in a mass buildup phase. At the current mass infall rate, we speculate that soon the disk will become too massive to be gravitationally stable.
Abstract We performed radiative transfer calculations and observing simulations to reproduce the 1.3 mm dust-continuum and C 18 O (2–1) images in the Class I protostar R CrA IRS7B-a, observed with ...the ALMA Large Program “Early Planet Formation in Embedded Disks (eDisk).” We found that a dust disk model passively heated by the central protostar cannot reproduce the observed peak brightness temperature of the 1.3 mm continuum emission (∼195 K), regardless of the assumptions about the dust opacity. Our calculation suggests that viscous accretion heating in the disk is required to reproduce the observed high brightness temperature. The observed intensity profile of the 1.3 mm dust-continuum emission along the disk minor axis is skewed toward the far side of the disk. Our modeling reveals that this asymmetric intensity distribution requires flaring of the dust along the disk vertical direction with the scale height following h / r ∼ r 0.3 as a function of radius. These results are in sharp contrast to those of Class II disks, which show geometrically flat dust distributions and lower dust temperatures. From our modeling of the C 18 O (2–1) emission, the outermost radius of the gas disk is estimated to be ∼80 au, which is larger than that of the dust disk (∼62 au), to reproduce the observed distribution of the C 18 O (2–1) emission in IRS 7B-a. Our modeling unveils a hot and thick dust disk plus a larger gas disk around one of the eDisk targets, which could be applicable to other protostellar sources in contrast to more evolved sources.
Abstract
Here we present high-resolution (15–24 au) observations of CO isotopologue lines from the Molecules with ALMA on Planet-forming Scales (MAPS) ALMA Large Program. Our analysis employs ...observations of the (
J
= 2–1) and (1–0) lines of
13
CO and C
18
O and the (
J
= 1–0) line of C
17
O for five protoplanetary disks. We retrieve CO gas density distributions, using three independent methods: (1) a thermochemical modeling framework based on the CO data, the broadband spectral energy distribution, and the millimeter continuum emission; (2) an empirical temperature distribution based on optically thick CO lines; and (3) a direct fit to the C
17
O hyperfine lines. Results from these methods generally show excellent agreement. The CO gas column density profiles of the five disks show significant variations in the absolute value and the radial shape. Assuming a gas-to-dust mass ratio of 100, all five disks have a global CO-to-H
2
abundance 10–100 times lower than the interstellar medium ratio. The CO gas distributions between 150 and 400 au match well with models of viscous disks, supporting the long-standing theory. CO gas gaps appear to be correlated with continuum gap locations, but some deep continuum gaps do not have corresponding CO gaps. The relative depths of CO and dust gaps are generally consistent with predictions of planet–disk interactions, but some CO gaps are 5–10 times shallower than predictions based on dust gaps. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.
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