Abstract High spatial resolution CO observations of midinclination (≈30°–75°) protoplanetary disks offer an opportunity to study the vertical distribution of CO emission and temperature. The asymmetry of line emission relative to the disk major axis allows for a direct mapping of the emission height above the midplane, and for optically thick, spatially resolved emission in LTE, the intensity is a measure of the local gas temperature. Our analysis of Atacama Large Millimeter/submillimeter Array archival data yields CO emission surfaces, dynamically constrained stellar host masses, and disk atmosphere gas temperatures for the disks around the following: HD 142666, MY Lup, V4046 Sgr, HD 100546, GW Lup, WaOph 6, DoAr 25, Sz 91, CI Tau, and DM Tau. These sources span a wide range in stellar masses (0.50–2.10 M ⊙ ), ages (∼0.3–23 Myr), and CO gas radial emission extents (≈200–1000 au). This sample nearly triples the number of disks with mapped emission surfaces and confirms the wide diversity in line emitting heights ( z / r ≈ 0.1 to ≳0.5) hinted at in previous studies. We compute the radial and vertical CO gas temperature distributions for each disk. A few disks show local temperature dips or enhancements, some of which correspond to dust substructures or the proposed locations of embedded planets. Several emission surfaces also show vertical substructures, which all align with rings and gaps in the millimeter dust. Combining our sample with literature sources, we find that CO line emitting heights weakly decline with stellar mass and gas temperature, which, despite large scatter, is consistent with simple scaling relations. We also observe a correlation between CO emission height and disk size, which is due to the flared structure of disks. Overall, CO emission surfaces trace ≈2–5× gas pressure scale heights (H g ) and could potentially be calibrated as empirical tracers of H g .
more »
« less
Mapping Protoplanetary Disk Vertical Structure with CO Isotopologue Line Emission
High-spatial-resolution observations of CO isotopologue line emission in protoplanetary disks at mid-inclinations (≈30°–75°) allow us to characterize the gas structure in detail, including radial and vertical substructures, emission surface heights and their dependencies on source characteristics, and disk temperature profiles. By combining observations of a suite of CO isotopologues, we can map the two-dimensional (
- Award ID(s):
- 1907832
- NSF-PAR ID:
- 10412161
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 948
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 60
- Size(s):
- ["Article No. 60"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
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, for12CO
J = 2–1,13COJ = 2–1, C18OJ = 2–1,H 2COJ = 30,3–20,2, and SOJ = 65–54, and constrain the CO midplane snow line to ∼130 au. We find Keplerian rotation around a protostar of 1.6 ± 0.4M ⊙using C18O. 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. -
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.more » « less
-
Abstract The water snowline in circumstellar disks is a crucial component in planet formation, but direct observational constraints on its location remain sparse owing to the difficulty of observing water in both young embedded and mature protoplanetary disks. Chemical imaging provides an alternative route to locate the snowline, and HCO + isotopologues have been shown to be good tracers in protostellar envelopes and Herbig disks. Here we present ∼0.″5 resolution (∼35 au radius) Atacama Large Millimeter/submillimeter Array (ALMA) observations of HCO + J = 4 − 3 and H 13 CO + J = 3 − 2 toward the young (Class 0/I) disk L1527 IRS. Using a source-specific physical model with the midplane snowline at 3.4 au and a small chemical network, we are able to reproduce the HCO + and H 13 CO + emission, but for HCO + only when the cosmic-ray ionization rate is lowered to 10 −18 s −1 . Even though the observations are not sensitive to the expected HCO + abundance drop across the snowline, the reduction in HCO + above the snow surface and the global temperature structure allow us to constrain a snowline location between 1.8 and 4.1 au. Deep observations are required to eliminate the envelope contribution to the emission and to derive more stringent constraints on the snowline location. Locating the snowline in young disks directly with observations of H 2 O isotopologues may therefore still be an alternative option. With a direct snowline measurement, HCO + will be able to provide constraints on the ionization rate.more » « less
-
more » « less
Abstract Deuterium fractionation provides a window into the thermal history of volatiles in the solar system and protoplanetary disks. While evidence of active molecular deuteration has been observed toward a handful of disks, it remains unclear whether this chemistry affects the composition of forming planetesimals due to limited observational constraints on the radial and vertical distribution of deuterated molecules. To shed light on this question, we introduce new Atacama Large Millimeter/submillimeter Array observations of DCO+and DCN
J = 2–1 at an angular resolution of 0.″5 (30 au) and combine them with archival data of higher energy transitions toward the protoplanetary disk around TW Hya. We carry out a radial excitation analysis assuming both LTE and non-LTE to localize the physical conditions traced by DCO+and DCN emission in the disk, thus assessing deuterium fractionation efficiencies and pathways at different disk locations. We find similar disk-averaged column densities of 1.9 × 1012and 9.8 × 1011cm−2for DCO+and DCN, with typical kinetic temperatures for both molecules of 20–30 K, indicating a common origin near the comet- and planet-forming midplane. The observed DCO+/DCN abundance ratio, combined with recent modeling results, provide tentative evidence of a gas-phase C/O enhancement within <40 au. Observations of DCO+and DCN in other disks, as well as HCN and HCO+, will be necessary to place the trends exhibited by TW Hya in context, and fully constrain the main deuteration mechanisms in disks.
