Turbulence is thought to be a key driver of the evolution of protoplanetary disks, regulating the mass accretion process, the transport of angular momentum, and the growth of dust particles. We ...intend to determine the magnitude of the turbulent motions in the outer parts (> 100 AU) of the disk surrounding DM Tau. Turbulent motions can be constrained by measuring the nonthermal broadening of line emission from heavy molecules. We used the IRAM Plateau de Bure interferometer to study emission from the CS molecule in the disk of DM Tau. High spatial (1.4 x 1 ") and spectral resolution (0.126 km/s) CS J=3-2 images provide constraints on the molecule distribution and velocity structure of the disk. A low sensitivity CS J=5-4 image was used in conjunction to evaluate the excitation conditions. We analyzed the data in terms of two parametric disk models, and compared the results with detailed time-dependent chemical simulations. The CS data confirm the relatively low temperature suggested by observations of other simple molecules. The intrinsic linewidth derived from the CS J=3-2 data is much larger than expected from pure thermal broadening. The magnitude of the derived nonthermal component depends only weakly on assumptions about the location of the CS molecules with respect to the disk plane. Our results indicate turbulence with a Mach number around 0.4 - 0.5 in the molecular layer. Geometrical constraints suggest that this layer is located near one scale height, in reasonable agreement with chemical model predictions.
Context.
The study of gas-rich debris discs is fundamental to characterising the transition between protoplanetary discs and debris discs.
Aims.
We determine the physical parameters of the brightest ...gas-rich debris disc orbiting HD 141569A.
Methods.
We analyse images from the NOrthern Extended Millimeter Array (NOEMA)
1
and the Atacama Large Millimeter/ submillimeter Array (ALMA) in
12
CO,
13
CO
J
= 2 → 1, and
13
CO
J
= 1 → 0 transitions. We incorporate ALMA archival data of the
12
CO
J
= 3 → 2 transition and present continuum maps at 0.87, 1.3, and 2.8 mm. We use simple parametric laws with the Diskfit code and MCMC exploration to characterise the gas disc parameters and report a first attempt to characterise its chemical content with IRAM-30 m.
Results.
The continuum emission is equally shared between a compact (≲50 au) and a smooth, extended dust component (~350 au). Large millimetre grains seem to dominate the inner regions, while the dust spectral index is marginally larger in the outer region. The
12
CO is optically thick, while
13
CO is optically thin with
τ
13
CO
~ 0.15 (C
18
O is not detected). The
13
CO surface density is constrained to be one order of magnitude smaller than around younger Herbig Ae stars, and we derive a gas mass
M
12
CO
= 10
−1
M
⊕
. We confirm the presence of a small CO cavity (
R
CO
= 17 ± 3 au), and find a possibly larger radius for the optically thin
13
CO
J
= 2 → 1 transition (35 ± 5 au). We show that the observed CO brightness asymmetry is coincident with the complex ring structures discovered with VLT/SPHERE in the inner 90 au. The
12
CO temperature
T
0
(100 au) ~ 30 K is lower than expected for a Herbig A0 star, and could be indicative of subthermal excitation.
Conclusions.
With the largest amount of dust and gas among hybrid discs, HD 141569A shows coincident characteristics of both protoplanetary discs (central regions), and debris discs at large distance. Together with its morphological characteristics and young age, it appears to be a good candidate to witness the transient phase of gas dissipation, with an apparently large gas-to-dust ratio (
G
∕
D
> 100) favouring a faster evolution of dust grains.
Protoplanetary disks are challenging objects for astrochemical models due to strong density and temperature gradients and due to the UV photons 2D propagation. In this paper, we have studied the ...importance of several model parameters on the predicted column densities of observed species. We considered: 1) 2-phase (gas and homogeneous grains) or 3-phase (gas, surface, and bulk of grains) models, 2) several initial compositions, 3) grain growth and dust settling, and 4) several cosmic-ray ionization rates. Our main result is that dust settling is the most crucial parameter. Including this effect renders the computed column densities sensitive to all the other model parameters, except cosmic-ray ionization rate. In fact, we found almost no effect of this parameter for radii larger than 10 au (the minimum radius studied here) except for N2H+. We also compared all our models with all the column densities observed in the protoplanetary disk around DM Tau and were not able to reproduce all the observations despite the studied parameters. N2H+ seems to be the most sensitive species. Its observation in protoplanetary disks at large radius could indicate enough N2 in the gas-phase (inhibited by the 3-phase model, but boosted by the settling) and a low electron abundance (favored by low C and S elemental abundances).
Context. Accurate temperature calculations for circumstellar disks are particularly important for their chemical evolution. Their temperature distribution is determined by the optical properties of ...the dust grains, which, among other parameters, depend on their radius. However, in most disk studies, only average optical properties and thus an average temperature is assumed to account for an ensemble of grains with different radii. Aims. We investigate the impact of subdividing the grain radius distribution into multiple sub-intervals on the resulting dust temperature distribution and spectral energy distribution (SED). Methods. The temperature distribution, the relative grain surface below a certain temperature, the freeze-out radius, and the SED were computed for two different scenarios: (1) Radius distribution represented by 16 logarithmically distributed radius intervals, and (2) radius distribution represented by a single grain species with averaged optical properties (reference). Results. Within the considered parameter range, i.e., of grain radii between 5 nm and 1 mm and an optically thin and thick disk with a parameterized density distribution, we obtain the following results: in optically thin disk regions, the temperature spread can be as large as ~ 63% and the relative grain surface below a certain temperature is lower than in the reference disk. With increasing optical depth, the difference in the midplane temperature and the relative grain surface below a certain temperature decreases. Furthermore, below ~ 20 K, this fraction is higher for the reference disk than for the case of multiple grain radii, while it shows the opposite behavior for temperatures above this threshold. The thermal emission in the case of multiple grain radii at short wavelengths is stronger than for the reference disk. The freeze-out radius (snowline) is a function of grain radius, spanning a radial range between the coldest and warmest grain species of ~ 30 AU.
Context. The overall properties of disks surrounding intermediate PMS stars (HAe) are not yet well constrained by current observations. The disk inclination, which significantly affects spectral ...energy distribution modeling, is often unknown. Aims. We attempted to resolve the disks around CQ Tau and MWC 758 to provide accurate constraints on the disk parameters, in particular the temperature and surface density distribution. Methods. We report arcsecond resolution observations of dust and CO line emissions with the IRAM array. We also searched for the HCO+ J = 1 $\rightarrow$ 0 transition. The disk properties are derived using a standard disk model. We use the Meudon PDR code to study the chemistry. Results. The two disks share some common properties. The mean CO abundance is low despite disk temperatures above the CO condensation temperature. Furthermore, the CO surface density and dust opacity have different radial dependence. The CQ Tau disk appears warmer and perhaps less dense than that of MWC 758. Modeling the chemistry, we find that photodissociation of CO is a viable mechanism to explain its low abundance. The photospheric flux is not sufficient for this: a strong UV excess is required. In CQ Tau, the high temperature is consistent with the expectation for a PDR. The PDR model has difficulty explaining the mild temperatures obtained in MWC 758, for which a low gas-to-dust ratio is preferred. A yet, unexplored alternative could be that, despite currently high gas temperatures CO remains trapped in grains, as the models suggest that large grains can be cold enough to prevent thermal desorption of CO. The low inclination of the CQ Tau disk, ~30°, challenges previous interpretations given for UX Ori – like luminosity variations of this star. Conclusions. We conclude that CO cannot be used as a simple tracer of gas-to-dust ratio, the CO abundance being affected by photodissociation and grain growth.
On the Nature of the T Tauri Triple System Beck, Tracy L.; Schaefer, G. H.; Guilloteau, S. ...
The Astrophysical journal,
10/2020, Volume:
902, Issue:
2
Journal Article
Peer reviewed
Open access
We present a multiwavelength analysis to reveal the nature of the enigmatic T Tauri triple star system. New optical and infrared measurements are coupled with archival X-ray, UV, and millimeter data ...sets to show the morphologies of disk material and outflow kinematics. A dark lane of obscuring material is seen in silhouette in several emission lines and in model-subtracted ALMA millimeter continuum dust residuals near the position of T Tau Sa+Sb, revealing the attenuating circumbinary ring around T Tau S. The flux variability of T Tau S is linked in part to the binary orbit; T Tau Sb brightens near orbital apastron as it emerges from behind circumbinary material. Outflow diagnostics confirm that T Tau N powers the blueshifted western outflow, and the T Tau S binary drives the northwest-southeastern flow. Analysis of the southern outflow shows periodic arcs ejected from the T Tau system. Correlation of these arc locations and tangential kinematics with the orbit timing suggests that launch of the last four southern outflow ejections is contemporaneous with, and perhaps triggered by, the T Tau Sa+Sb binary periastron passage. We present a geometry of the T Tau triple that has the southern components foreground to T Tau N, obscured by a circumbinary ring, with misaligned disks and interacting outflows. Particularly, a wind from T Tauri Sa that is perpendicular to its circumstellar disk might interact with the circumbinary material, which may explain conflicting high-contrast measurements of the system outflows in the literature. T Tauri is an important laboratory for understanding early dynamical processes in young multiple systems. We discuss the historical and future characteristics of the system in this context.
Context. To understand how planets form in protoplanetary disks, it is necessary to characterize their gas and dust distribution and masses. This requires a combination of high-resolution dust ...continuum and molecular line interferometric observations, coupled with advanced theoretical models of protoplanetary disk physics, chemical composition, and radiative transfer. Aims. We aim to constrain the gas density and temperature distributions as well as gas masses in several T Tauri protoplanetary disks located in Taurus. We use the 12CO, 13CO, and C18O (2–1) isotopologue emission observed at 0.9″ with the IRAM NOrthern Extended Millimeter Array (NOEMA) as part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution PIs: P. Caselli & Th. Henning). Our sample consists of Class II disks with no evidence of strong radial substructures. We use these data to constrain the thermal and chemical structure of these disks through theoretical models for gas emission. Methods. To fit the combined optically thick and thin CO line data in Fourier space, we developed the DiskCheF code, which includes the parameterized disk physical structure, machine-learning (ML) accelerated chemistry, and the RADMC-3D line radiative transfer module. A key novelty of DiskCheF is the fast and feasible ML-based chemistry trained on the extended grid of the disk physical-chemical models precomputed with the ANDES2 code. This ML approach allows complex chemical kinetics models to be included in a time-consuming disk fitting without the need to run a chemical code. Results. We present a novel approach to incorporate chemistry into disk modeling without the need to explicitly calculate a chemical network every time. Using this new disk modeling tool, we successfully fit the 12CO, 13CO, and C18O (2-1) data from the CI, CY, DL, DM, DN, and IQ Tau disks. The combination of optically thin and optically thick CO lines allows us to simultaneously constrain the disk temperature and mass distribution, and derive the CO-based gas masses. The best-fit disk gas masses range between 0.005 and 0.04 M⊙. These values are in reasonable agreement with the disk dust masses rescaled by a factor of 100 as well as with other indirect gas measurements via, for example, modeling of the wavelength dependence of the dust continuum emission radii, and HD and CO isotopologue emission.
Context. The physics and chemistry of planet-forming disks are far from being fully understood. To make further progress, both broad line surveys and observations of individual tracers in a ...statistically significant number of disks are required. Aims. Our aim is to perform a line survey of eight planet-forming Class II disks in Taurus with the IRAM NOrthern Extended Millimeter Array (NOEMA), as a part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution; PIs: P. Caselli and Th. Henning). Methods. Compact and extended disks around T Tauri stars CI, CY, DG, DL, DM, DN, IQ Tau, and UZ Tau E are observed in ~80 lines from > 20 C-, O,- N-, and S-bearing species. The observations in four spectral settings at 210–280 GHz with a 1σ rms sensitivity of ~8–12 mJy beam−1 at a 0.9″ and 0.3 km s−1 resolution will be completed in 2024. The uv visibilities are fitted with the DiskFit model to obtain key stellar and disk properties. Results. In this first paper, the combined 12CO, 13CO, and C18O J = 2–1 data are presented. We find that the CO fluxes and disk masses inferred from dust continuum tentatively correlate with the CO emission sizes. We constrained dynamical stellar masses, geometries, temperatures, the CO column densities, and gas masses for each disk. The best-fit temperatures at 100 au are ~ 17–37 K, and decrease radially with the power-law exponent q ~ 0.05–0.76. The inferred CO column densities decrease radially with the power-law exponent p ~ 0.2–3.1. The gas masses estimated from 13CO (2–1) are ~0.001–0.2 M⊙. Conclusions. Using NOEMA, we confirm the presence of temperature gradients in our disk sample. The best-fit CO column densities point to severe CO freeze-out in these disks. The DL Tau disk is an outlier, and has either stronger CO depletion or lower gas mass than the rest of the sample. The CO isotopologue ratios are roughly consistent with the observed values in disks and the low-mass star-forming regions. The high 13CO/C18O ratio of ~23 in DM Tau could be indicative of strong selective photodissociation of C18O in this disk.
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