The precursors to larger, biologically relevant molecules are detected throughout interstellar space, but determining the presence and properties of these molecules during planet formation requires ...observations of protoplanetary disks at high angular resolution and sensitivity. Here, we present 0.″3 observations of HC3N, CH3CN, and c-C3H2 in five protoplanetary disks observed as part of the Molecules with ALMA at Planet-forming Scales (MAPS) Large Program. We robustly detect all molecules in four of the disks (GM Aur, AS 209, HD 163296, and MWC 480) with tentative detections of c-C3H2 and CH3CN in IM Lup. We observe a range of morphologies—central peaks, single or double rings—with no clear correlation in morphology between molecule or disk. Emission is generally compact and on scales comparable with the millimeter dust continuum. We perform both disk-integrated and radially resolved rotational diagram analysis to derive column densities and rotational temperatures. The latter reveals 5–10 times more column density in the inner 50–100 au of the disks when compared with the disk-integrated analysis. We demonstrate that CH3CN originates from lower relative heights in the disks when compared with HC3N, in some cases directly tracing the disk midplane. Finally, we find good agreement between the ratio of small to large nitriles in the outer disks and comets. Our results indicate that the protoplanetary disks studied here are host to significant reservoirs of large organic molecules, and that this planet- and comet-building material can be chemically similar to that in our own solar system. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.
The physical and chemical conditions in the protoplanetary disk set the initial conditions for planet formation. Constraining the properties of disks is of key importance for understanding how ...planets assemble. Observations of molecular lines in disks provide valuable information on disk properties. This thesis presents ALMA observations, analysis and modelling of molecular line emission from four disks that all exhibit evidence for forming planets. Using the first-ever observations of 13C17O in protoplanetary disks, the CO gas mass of the HD 163296 and HL Tau disks are robustly constrained. The new masses are a factor of 2-10 times higher than existing estimates using C18O, and highlight the potential gravitational instability of the HL Tau disk. Analysis of the radial distribution of HCO+ and H13CO+ in the HD 97048 disk reveals a low ratio that can be explained via chemical fractionation. This indicates that the gas temperature in the outer disk is low (approx. 10 K) despite this disk being hosted by an A-type star. Both silicon and sulphur bearing volatiles are observed to be significantly depleted in disks, similar to dark clouds. Multiple lines of SO and SiO are targeted towards HD 100546 and HD 97048. The detection of the shock tracer SO in the HD 100546 disk is attributed to either a disk wind or a circumplanetary disk. Complementary chemical modelling reveals the molecular carriers of S and Si in the two sources, and predicts SiS as tracer of S and Si in disks. This thesis shows that 13C17O is a robust tracer of disk gas mass, HCO+ isotopologue emission may trace reservoirs of cold gas in typically warm disks, and Si and S bearing molecules are useful probes of shock induced structures such as circumplanetary disks.
Abstract
ALMA observations have shown that there is discrepancy between the disk mass estimate from CO emission and disk masses estimated from other tracers. This discrepancy has been interpreted as ...lower than expected CO abundance in the warm, surface layers of the disk. Recent work by Ruaud et al. claims that the low observed C
18
O fluxes can be explained with a ISM abundance of CO, that is 10
−4
w.r.t. H
2
by including hydrostatic equilbrium in the model density setup. We show that the Ruaud et al. low CO fluxes are due to an unrealistic temperature structure in the outer disk, due to an interaction of their dust model and hydrostatic equilibrium at their inner model edge. Furthermore, we show with our own modeling that a parametric model does a better job at matching the measured outer disk temperature structure.
Abstract
Observationally locating the position of the H
2
O snowline in protoplanetary disks is crucial for understanding planetesimal and planet formation processes, and the origin of water on the ...Earth. In our studies, we conducted calculations of chemical reactions and water line profiles in protoplanetary disks, and identified that ortho/para-H
2
16
O, H
2
18
O lines with small Einstein A coefficients and relatively high upper state energies are dominated by emission from the hot midplane region inside the H
2
O snowline. Therefore, through analyzing their line profiles the position of the H
2
O snowline can be located. Moreover, because the number density of the H
2
18
O is much smaller than that of H
2
16
O, the H
2
18
O lines can trace deeper into the disk and thus they are potentially better probes of the exact position of the H
2
O snowline in disk midplane.
Planets form in dusty, gas-rich disks around young stars, while at the same time, the planet formation process alters the physical and chemical structure of the disk itself. Embedded planets will ...locally heat the disk and sublimate volatile-rich ices, or in extreme cases, result in shocks that sputter heavy atoms such as Si from dust grains. This should cause chemical asymmetries detectable in molecular gas observations. Using high-angular-resolution ALMA archival data of the HD 169142 disk, we identify compact SO J=8\(_8\)-7\(_7\) and SiS J=19-18 emission coincident with the position of a \({\sim}\)2 M\(_{\rm{Jup}}\) planet seen as a localized, Keplerian NIR feature within a gas-depleted, annular dust gap at \({\approx}\)38 au. The SiS emission is located along an azimuthal arc and has a similar morphology as a known \(^{12}\)CO kinematic excess. This is the first tentative detection of SiS emission in a protoplanetary disk and suggests that the planet is driving sufficiently strong shocks to produce gas-phase SiS. We also report the discovery of compact \(^{12}\)CO and \(^{13}\)CO J=3-2 emission coincident with the planet location. Taken together, a planet-driven outflow provides the best explanation for the properties of the observed chemical asymmetries. We also resolve a bright, azimuthally-asymmetric SO ring at \({\approx}\)24 au. While most of this SO emission originates from ice sublimation, its asymmetric distribution implies azimuthal temperature variations driven by a misaligned inner disk or planet-disk interactions. Overall, the HD 169142 disk shows several distinct chemical signatures related to giant planet formation and presents a powerful template for future searches of planet-related chemical asymmetries in protoplanetary disks.
The composition of a forming planet is set by the material it accretes from its parent protoplanetary disk. Therefore, it is crucial to map the chemical make-up of the gas in disks to understand the ...chemical environment of planet formation. This paper presents molecular line observations taken with the Atacama Large Millimeter/submillimeter Array of the planet-hosting disk around the young star HD 169142. We detect N2H+, CH3OH, CI, DCN, CS, C34S, 13CS, H2CS, H2CO, HC3N and c-C3H2 in this system for the first time. Combining these data with the recent detection of SO and previously published DCO+ data, we estimate the location of H2O and CO snowlines and investigate radial variations in the gas phase C/O ratio. We find that the HD 169142 disk has a relatively low N2H+ flux compared to the disks around Herbig stars HD 163296 and MWC 480 indicating less CO freeze-out and place the CO snowline beyond the millimetre disk at ~150 au. The detection of CH3OH from the inner disk is consistent with the H2O snowline being located at the edge of the central dust cavity at ~20 au. The radially varying CS/SO ratio across the proposed H2O snowline location is consistent with this interpretation. Additionally, the detection of CH3OH in such a warm disk adds to the growing evidence supporting the inheritance of complex ices in disks from the earlier, colder stages of star formation. Finally, we propose that the giant HD 169142 b located at 37 au is forming between the CO2 and H2O snowlines where the local elemental make of the gas is expected to have C/O=1.0.
We present the first detection of the 13C17O J=3-2 transition toward the HL Tau protoplanetary disc. We find significantly more gas mass (at least a factor of ten higher) than has been previously ...reported using C18O emission. This brings the observed total disc mass to 0.2 M, which we consider to be a conservative lower limit. Our analysis of the Toomre Q profile suggests that this brings the disc into the regime of gravitational instability. The radial region of instability (50-110 au) coincides with the location of a proposed planet-carved gap in the dust disc and a spiral in the gas. We, therefore, propose that if the origin of the gap is confirmed to be due to a forming giant planet, then it is likely to have formed via the gravitational fragmentation of the protoplanetary disc.
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