Spatially resolved continuum observations of planet-forming disks show prominent ring and gap structures in their dust distribution. However, the picture from gas observations is much less clear and constraints on the radial gas density structure (i.e. gas gaps) remain rare and uncertain. We want to investigate the importance of thermo-chemical processes for the interpretation of high-spatial-resolution gas observations of planet-forming disks and their impact on derived gas properties. We apply the radiation thermo-chemical disk code ProDiMo (PROtoplanetary DIsk MOdel) to model self-consistently the dust and gas disk of HD 163296, using the DSHARP gas and dust observations. With this model we investigate the impact of dust gaps and gas gaps, considering chemistry and heating/cooling processes, on the observables and the derived gas properties. We find distinct peaks in the radial line intensity profiles of the CO line data of HD 163296 at the location of the dust gaps. Our model indicates that those peaks are not only a consequence of a gas temperature increase within the gaps but are mainly caused by the absorption of line emission from the back side of the disk by the dust rings. For two of the three prominent dust gaps in HD 163296, we find that thermo-chemical effects are negligible for deriving density gradients via measurements of the rotation velocity. However, for the gap with the highest dust depletion, the temperature gradient can be dominant and needs to be considered to derive accurate gas density profiles. Self-consistent gas and dust thermo-chemical modelling in combination with high-quality observations of multiple molecules are necessary to accurately derive gas gap depths and shapes. This is crucial to determine the origin of gaps and rings in planet-forming disks and to improve the mass estimates of forming planets if they are the cause of the gap.
Rings are the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, but their origin is still hotly debated. In this paper, we identify dust substructures in 12 disks and measure their properties to investigate how they form. This subsample of disks is selected from a high-resolution ($\sim0.12''$) ALMA 1.33 mm survey of 32 disks in the Taurus star-forming region, which was designed to cover a wide range of sub-mm brightness and to be unbiased to previously known substructures. While axisymmetric rings and gaps are common within our sample, spiral patterns an…
One of the most intriguing properties of the GD-1 stellar stream is the existence of three gaps. If these gaps were formed by close encounters with dark matter subhalos, the GD-1 stream opens an exciting window through which we can see the size, mass, and velocity distributions of the dark matter subhalos in the Milky Way. However, in order to use the GD-1 stream as a probe of the dark matter substructure, we need to disprove that these gaps are not due to the perturbations from baryonic components of the Milky Way. Here we ran a large number of test particle simulations to investigate the pro…
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 $^{13}$CO and C$^{18}$O ($J$=2-1), (1-0), and C$^{17}$O (1-0) line observations of five protoplanetary disks. We retrieve CO gas density distributions, using three independent methods: (1) a thermo-chemical modeling framework based on the CO data, the broadband spectral energy distribution, and the mm-continuum emission; (2) an empirical temperature distribution based on optically thick CO lines; and (3) a direct …
Recent investigation of the extinction law in 30 Dor and the Tarantula Nebula, at optical and near infrared (NIR) wavelengths, has revealed a ratio of total to selective extinction R_V=A_V/E(B-V) of about 4.5. This indicates a larger fraction of big grains than in the Galactic diffuse interstellar medium (ISM). Possible origins include coalescence of small grains, small grain growth, selective destruction of small grains, and fresh injection of big grains. From a study of the ultraviolet extinction properties of three massive stars in the 30 Dor nebula (R139, R140, R145), observed with the Int…
Gravitational collapse of molecular cloud or cloud core/clump may lead to the formation of geometrically flattened, rotating accretion flow surrounding the new born star or star cluster. Gravitational instability may occur in such accretion flow when the gas to stellar mass ratio is high (e.g. over $\sim$10\%). This paper takes the OB cluster-forming region G10.6-0.4 as an example. We introduce the enclosed gas mass around its central ultra compact (UC) H\textsc{ii} region, addresses the gravitational stability of the accreting gas, and outline the observed potential signatures of gravitationa…
ALMA has found multiple dust gaps and rings in a number of protoplanetary disks in continuum emission at millimeter wavelengths. The origin of such structures is in debate. Recently, we documented how one super-Earth planet can open multiple (up to five) dust gaps in a disk with low viscosity ($α\lesssim10^{-4}$). In this paper, we examine how the positions, depths, and total number of gaps opened by one planet depend on input parameters, and apply our results to real systems. Gap locations (equivalently, spacings) are the easiest metric to use when making comparisons between theory and observ…
Complex nitriles, such as HC3N, and CH3CN, are observed in a wide variety of astrophysical environments, including at relatively high abundances in photon-dominated regions (PDR) and the UV exposed atmospheres of planet-forming disks. The latter have been inferred to be oxygen-poor, suggesting that these observations may be explained by organic chemistry in C-rich environments. In this study we first explore if the PDR complex nitrile observations can be explained by gas-phase PDR chemistry alone if the elemental C/O ratio is elevated. In the case of the Horsehead PDR, we find that gas-phase c…
We present VLT/MUSE observations of NGC 2070, the dominant ionizing nebula of 30 Doradus in the LMC, plus HST/STIS spectroscopy of its central star cluster R136. Integral Field Spectroscopy (MUSE) and pseudo IFS (STIS) together provides a complete census of all massive stars within the central 30x30 parsec^2 of the Tarantula. We discuss the integrated far-UV spectrum of R136, of particular interest for UV studies of young extragalactic star clusters. Strong HeII 1640 emission at very early ages (1-2 Myr) from very massive stars cannot be reproduced by current population synthesis models, even …
Protoplanetary discs are now routinely observed and exoplanets, after the numerous indirect discoveries, are starting to be directly imaged. To better understand the planet formation process, the next step is the detection of forming planets or of signposts of young planets still in their disc, such as gaps. A spectacular example is the ALMA science verification image of HL Tau showing numerous gaps and rings in its disc. To study the observability of planet gaps, we ran 3D hydrodynamical simulations of a gas and dust disc containing a 5 M J gap-opening planet and characterised the spatial dis…
The "Disk Substructures at High Angular Resolution Project" (DSHARP) has revealed an abundance and ubiquity of rings and gaps over a large sample of young planet-forming disks, which are hypothesised to be induced by the presence of forming planets. In this context, we present the first attempt to directly image these young companions for 10 of the DSHARP disks, by using NaCo/VLT high contrast observations in L'-band instrument and angular differential imaging techniques. We report the detection of a point-like source candidate at 1.1" (174.9 au) for RU Lup, and at 0.42" (55 AU) for Elias 24. …
Equatorial density enhancements (EDEs) are a very common astronomical phenomenon. Studies of the circumstellar environments (CSE) of young stellar objects and of evolved stars have shown that these objects often possess these features. These are believed to originate from different mechanisms, ranging from binary interactions to the gravitational collapse of interstellar material. Quantifying the effect of the presence of this type of EDE on the observables is essential for a correct interpretation of high-resolution data. We seek to investigate the manifestation in the observables of a circum…
We have analyzed the HCO+ (1-0) data of the Class I-II protostar, HL Tau, obtained from the Atacama Large Millimeter/Submillimeter Array long baseline campaign. We generated the HCO+ image cube at an angular resolution of ~0.07 (~10 AU), and performed azimuthal averaging on the image cube to enhance the signal-to-noise ratio and measure the radial profile of the HCO+ integrated intensity. Two gaps at radii of ~28 AU and ~69 AU and a central cavity are identified in the radial intensity profile. The inner HCO+ gap is coincident with the millimeter continuum gap at a radius of 32 AU. The outer H…
The disks around Herbig Ae/Be stars are commonly divided into group I and group II based on their far-infrared spectral energy distribution, and the common interpretation for that is flared and flat disks. Recent observations suggest that many flaring disks have gaps, whereas flat disks are thought to be gapless. The different groups of objects can be expected to have different structural signatures in high-angular-resolution data. Over the past 10 years, the MIDI instrument on the Very Large Telescope Interferometer has collected observations of several tens of protoplanetary disks. We model …
We present simulations of the capabilities of the Next Generation Very Large Array to image at high angular resolution substructures in the dust emission of protoplanetary disks. The main goal of this study is to investigate the kinds of substructures that are expected by state-of-the-art 3D simulations of disks and that an instrument like the ngVLA, with its current design, can detect. The disk simulations adopted in this investigation consist of global 3D radiation-hydrodynamics models with embedded particles, the latter representing dust grains. Our work shows that the ngVLA can detect and …
[Abridged] Aims: We provide predictions for ALMA observations of planet gaps that account for the specific spatial distribution of dust that results from consistent gas+dust dynamics. Methods: In a previous work, we ran full 3D, two-fluid Smoothed Particle Hydrodynamics (SPH) simulations of a planet embedded in a gas+dust T Tauri disk for different planet masses and grain sizes. In this work, the resulting dust distributions are passed to the Monte Carlo radiative transfer code MCFOST to construct synthetic images in the ALMA wavebands. We then use the ALMA simulator to produce images that inc…
Radial substructures in circumstellar disks are now routinely observed by ALMA. There is also growing evidence that disk winds drive accretion in such disks. We show through 2D (axisymmetric) simulations that rings and gaps develop naturally in magnetically coupled disk-wind systems on the scale of tens of au, where ambipolar diffusion (AD) is the dominant non-ideal MHD effect. In simulations where the magnetic field and matter are moderately coupled, the disk remains relatively laminar with the radial electric current steepened by AD into a thin layer near the midplane. The toroidal magnetic …
We present 5 to 36 micron mid-infrared spectra of 82 young stars in the ~2 Myr old Chamaeleon I star-forming region, obtained with the Spitzer Infrared Spectrograph (IRS). We have classified these objects into various evolutionary classes based on their spectral energy distributions and the spectral features seen in the IRS spectra. We have analyzed the mid-IR spectra of Class II objects in Chamaeleon I in detail, in order to study the vertical and radial structure of the protoplanetary disks surrounding these stars. We find evidence for substantial dust settling in most protoplanetary disks i…
Filaments play an important role in star formation, but the formation process of filaments themselves is still unclear. The high-mass star forming clump G286.21+0.17 (G286 for short) that contains an "L" type filament was thought to undergo global collapse. Our high resolution ALMA band 3 observations resolve the gas kinematics of G286 and reveal two sub-clumps with very different velocities inside it. We find that the "blue profile" (an indicator of gas infall) of HCO+ lines in single dish observations of G286 is actually caused by gas emission from the two sub-clumps rather than gas infall. …
Understanding the temperature structure of protoplanetary disks is key to interpreting observations, predicting the physical and chemical evolution of the disk, and modeling planet formation processes. In this study, we constrain the two-dimensional thermal structure of the disk around Herbig Ae star HD 163296. Using the thermo-chemical code RAC2D, we derive a thermal structure that reproduces spatially resolved ALMA observations (~0.12 arcsec (13 au) - 0.25 arcsec (26 au)) of CO J = 2-1, 13CO J = 1-0, 2-1, C18O J = 1-0, 2-1, and C17O J = 1-0, the HD J = 1-0 flux upper limit, the spectral ener…
In recent years, ALMA has been able to observe large-scale substructures within protoplanetary disks. Comparison with the predictions from models of planet-disk interaction has indicated that most of these disk substructures can be explained by the presence of planets with the mass of Neptune or larger at orbital radii of $\approx 5 - 100$ au. Better resolution is needed to observe structures closer to the star, where terrestrial planets are expected to form, as well as structures opened by planets with masses lower than Neptune. We investigate the capabilities of a possible extension to ALMA …
The paper presents new high angular resolution ALMA 1.3 mm dust continuum observations of the protoplanetary system AS 209 in the Ophiuchus star forming region. The dust continuum emission is characterized by a main central core and two prominent rings at $r = 75\,$au and $r = 130\,$au intervaled by two gaps at at $r = 62\,$au and $r = 103\,$au. The two gaps have different widths and depths, with the inner one being narrower and shallower. We determined the surface density of the millimeter dust grains using the 3D radiative transfer disk code \textsc{dali}. According to our fiducial model the…
We present scattered light images of the TW Hya disk performed with SPHERE in PDI mode at 0.63, 0.79, 1.24 and 1.62 micron. We also present H2/H3-band ADI observations. Three distinct radial depressions in the polarized intensity distribution are seen, around 85, 21, and 6~au. The overall intensity distribution has a high degree of azimuthal symmetry; the disk is somewhat brighter than average towards the South and darker towards the North-West. The ADI observations yielded no signifiant detection of point sources in the disk. Our observations have a linear spatial resolution of 1 to 2au, simi…
Molecular diagnostics for the mid-infrared emission of planet-forming disks. Carbon and oxygen elemental abundances
Kapteyn Astronomical Institute, Rijksuniversiteit Groningen（格罗宁根大学卡普坦天文研究所）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Max-Planck Institut für Extraterrestrische Physik (MPE)（马克斯·普朗克地外物理研究所）；Space Research Institute, Austrian Academy of Sciences（奥地利科学院空间研究所）；University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München（慕尼黑大学物理学院大学天文台）；Department of Physics and Astronomy, University of Exeter（埃克塞特大学物理与天文学系）；Department of Astronomy, University of Michigan（密歇根大学天文学系）；Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale（巴黎萨克雷大学、法国国家科学研究中心、空间天体物理学研究所）
We present two-dimensional hydrodynamic simulations of self-gravitating protostellar disks subject to axisymmetric infall from envelopes and irradiation from the central star, to explore disk fragmentation due to gravitational instability (GI), and the fragmented clump evolution. We assume that the disk is built gradually and smoothly by the infall, resulting in good numerical convergence. We confirm that for disks around solar-mass stars, infall at high rates at radii beyond ~50 AU leads to disk fragmentation. At lower infall rates <1e-5 Msun/yr, however, irradiation suppresses fragmentation.…
The Molecules with ALMA at Planet-forming Scales (MAPS) Large Program provides a unique opportunity to study the vertical distribution of gas, chemistry, and temperature in the protoplanetary disks around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480. By using the asymmetry of molecular line emission relative to the disk major axis, we infer the emission height ($z$) above the midplane as a function of radius ($r$). Using this method, we measure emitting surfaces for a suite of CO isotopologues, HCN, and C$_2$H. We find that $^{12}$CO emission traces the most elevated regions with $z/r > 0.3$…
High contrast imaging instruments such as GPI and SPHERE are discovering gap structures in protoplanetary disks at an ever faster pace. Some of these gaps may be opened by planets forming in the disks. In order to constrain planet formation models using disk observations, it is crucial to find a robust way to quantitatively back out the properties of the gap-opening planets, in particular their masses, from the observed gap properties, such as their depths and widths. Combing 2D and 3D hydrodynamics simulations with 3D radiative transfer simulations, we investigate the morphology of planet-ope…
Planet-forming disks of gas and dust around young stars contain polycyclic aromatic hydrocarbons (PAHs). We aim to characterize how the charge state of PAHs can be used as a probe of flows of gas through protoplanetary gaps. In this context, our goal is to understand the PAH spectra of four transitional disks. In addition, we want to explain the observed correlation between PAH ionization (traced by the 6.2/11.3 feature ratio) and the disk mass (traced by the 1.3 mm luminosity). We implement a model to calculate the charge state of PAHs in the radiative transfer code MCMax. The emission spectr…
High-contrast imaging in the visible and near-infrared (VIS/NIR) has revealed the presence of a plethora of substructures in circumstellar disks (CSDs). One of the most commonly observed substructures are concentric gaps that may hint at the presence of embedded forming planets. However, direct detections of them are rare, and thus ambiguity regarding the origin of most gap features remains. The aim of this study is to investigate the capabilities of high-contrast VIS/NIR imaging of directly detecting and characterizing low-mass giant planets in gaps. To this end, a grid of models of protoplan…
The degree to which the formation and evolution of clouds and filaments in the interstellar medium is regulated by magnetic fields remains an open question. Yet the fundamental properties of the fields (strength and 3D morphology) are not readily observable. We investigate the potential for recovering magnetic field information from dust polarization, the Zeeman effect, and the Faraday rotation measure ($RM$) in a SILCC-Zoom magnetohydrodynamic (MHD) filament simulation. The object is analyzed at the onset of star formation, and it is characterized by a line-mass of about M/L $\sim 63\ M_{\odo…
We analyze samples of Spitzer Infrared Spectrograph (IRS) spectra of T Tauri stars in the Ophiuchus, Taurus, and Chamaeleon I star-forming regions, whose median ages lie in the <1 to 2 Myr range. The median mid-infrared spectra of objects in these three regions are similar in shape, suggesting, on average, similar disk structures. When normalized to the same stellar luminosity, the medians follow each other closely, implying comparable mid-infrared excess emission from the circumstellar disks. We use the spectral index between 13 and 31 micron and the equivalent width of the 10 micron silicate…
We conducted a 12-month monitoring campaign of 33 T Tauri stars (TTS) in Taurus. Our goal was to monitor objects that possess a disk but have a weak Halpha line, a common accretion tracer for young stars, to determine whether they host a passive circumstellar disk. We used medium-resolution optical spectroscopy to assess the objects' accretion status and to measure the Halpha line. We found no convincing example of passive disks; only transition disk and debris disk systems in our sample are non-accreting. Among accretors, we find no example of flickering accretion, leading to an upper limit o…
