Searching for chemical signatures of planet formation

AbstractHigh spatial resolution observations with ALMA and VLT/SPHERE show gaps and rings in continuum emission of protoplanetary disks, possibly indicating ongoing planet formation. However, it is still unclear if the gas follows the dust distribution. We present radiation thermo-chemical models for the disk of HD 163296 to study the impact of dust and gas gaps on the chemistry and molecular line emission. We compare a model with only dust gaps to a model that also has gas gaps. In both models, rings and gaps are visible in (sub)mm molecular line emission. Due to chemistry, certain molecules are sensitive to dust gaps where others are more sensitive to gas depletion. Observations of multiple molecules might allow to accurately determine the degree of gas depletion within the dust gaps, information crucial to discriminate between gap formation theories (e.g. planets, ice lines).

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Planet formation in action: resolved gas and dust images of a transitional disk and its cavity

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313007989 ◽

2013 ◽

Vol 8 (S299) ◽

pp. 90-93

Author(s):

Nienke van der Marel ◽

Ewine F. van Dishoeck ◽

Simon Bruderer ◽

Til Birnstiel ◽

Paola Pinilla ◽

...

Keyword(s):

Planet Formation ◽

Early Stage ◽

Continuum Emission ◽

Dust Trapping ◽

Spatially Resolved ◽

First Results ◽

Disk Evolution ◽

Gas Cavity ◽

Dust Distribution ◽

The Continuum

AbstractPlanet formation and clearing of protoplanetary disks is one of the long standing problems in disk evolution theory. The best test of clearing scenarios is observing systems that are most likely to be actively forming planets: the transitional disks with large inner dust cavities. We present the first results of our ALMA (Atacama Large Millimeter/submillimeter Array) Cycle 0 program using Band 9, imaging the Herbig Ae star Oph IRS 48 in CO 6−5 and the submillimeter continuum in the extended configuration. The resulting ~0.2″ spatial resolution completely resolves the cavity of this disk in the gas and the dust. The gas cavity of IRS 48 is half as large as the dust cavity, ruling out grain growth and photoevaporation as the primary cause of the truncation. On the other hand, the continuum emission reveals an unexpected large azimuthal asymmetry and steep edges in the dust distribution along the ring, suggestive of dust trapping. We will discuss the implications of the combined gas and dust distribution for planet formation at a very early stage. This is one of the first transition disks with spatially resolved gas inside the cavity, demonstrating the superb capabilities of the Band 9 receivers.

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Extragalactic science with ALMA

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312009696 ◽

2011 ◽

Vol 7 (S284) ◽

pp. 494-495

Author(s):

George J. Bendo ◽

Keyword(s):

Molecular Clouds ◽

High Redshift ◽

Atacama Desert ◽

Line Emission ◽

Continuum Emission ◽

Synchrotron Emission ◽

Molecular Line ◽

Molecular Lines ◽

Nearby Galaxies ◽

Detailed Imaging

AbstractThe Atacama Large Millimeter/submillimeter Array (ALMA) is a telescope comprising 66 antennas that is located in the Atacama Desert in Chile, one of the driest locations on Earth. When the telescope is fully operational, it will perform observations over ten receiver bands at wavelengths from 9.5-0.32 mm (31-950 GHz) with unprecedented sensitivities to continuum emission from cold (<20 K) dust, Bremsstrahlung, and synchrotron emission as well as submillimetre and millimetre molecular lines. With baselines out to 16km and dynamic reconfiguration, ALMA will achieve spatial resolutions ranging from 3″ to 0.010″, allowing for detailed imaging of continuum or molecular line emission from 0.1-1 kpc scale gas and dust discs in high-redshift sources or 10-100 pc scale molecular clouds and substructures within nearby galaxies. Science observations started on 30 September 2011 with 16 antennas and four receiver bands on baselines up to 400 m. The telescope's capabilities will steadily improve until full operations begin in 2013.

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Discovery of Molecular-line Polarization in the Disk of TW Hya

The Astrophysical Journal ◽

10.3847/1538-4357/ac2503 ◽

2021 ◽

Vol 922 (2) ◽

pp. 139

Author(s):

Richard Teague ◽

Charles L. H. Hull ◽

Stéphane Guilloteau ◽

Edwin A. Bergin ◽

Anne Dutrey ◽

...

Keyword(s):

Linear Polarization ◽

Line Emission ◽

Emission Lines ◽

Continuum Emission ◽

Azimuthal Dependence ◽

Molecular Line ◽

Polarization Fraction ◽

Co Emission ◽

Higher Sensitivity ◽

The Continuum

Abstract We report observations of polarized line and continuum emission from the disk of TW Hya using the Atacama Large Millimeter/submillimeter Array. We target three emission lines, 12CO (3–2), 13CO (3–2), and CS (7–6), to search for linear polarization due to the Goldreich–Kylafis effect, while simultaneously tracing the continuum polarization morphology at 332 GHz (900 μm), achieving a spatial resolution of 0.″5 (30 au). We detect linear polarization in the dust continuum emission; the polarization position angles show an azimuthal morphology, and the median polarization fraction is ∼0.2%, comparable to previous, lower frequency observations. Adopting a “shift-and-stack” technique to boost the sensitivity of the data, combined with a linear combination of the Q and U components to account for their azimuthal dependence, we detect weak linear polarization of 12CO and 13CO line emission at a ∼10σ and ∼5σ significance, respectively. The polarization was detected in the line wings, reaching a peak polarization fraction of ∼5% and ∼3% for the two molecules between disk radii of 0.″5 and 1″. The sign of the polarization was found to flip from the blueshifted side of the emission to the redshifted side, suggesting a complex, asymmetric polarization morphology. Polarization is not robustly detected for the CS emission; however, a tentative signal, comparable in morphology to that found for the 12CO and 13CO emission, is found at a ≲3σ significance. We are able to reconstruct a polarization morphology, consistent with the azimuthally averaged profiles, under the assumption that this is also azimuthally symmetric, which can be compared with future higher-sensitivity observations.

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Synthetic line and continuum observations of simulated turbulent clouds: the apparent widths of filaments

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3111 ◽

2020 ◽

Vol 499 (3) ◽

pp. 3728-3737

Author(s):

F D Priestley ◽

A P Whitworth

Keyword(s):

Radial Velocity ◽

Surface Density ◽

Line Emission ◽

Continuum Emission ◽

Full Time ◽

Molecular Line ◽

Line Intensities ◽

Hydrodynamical Simulations ◽

Proper Account ◽

Synthetic Line

ABSTRACT Filamentary structures are ubiquitous in observations of real molecular clouds and also in simulations of turbulent, self-gravitating gas. However, making comparisons between observations and simulations is complicated by the difficulty of estimating volume densities observationally. Here, we have post-processed hydrodynamical simulations of a turbulent isothermal molecular cloud, using a full time-dependent chemical network. We have then run radiative transfer models to obtain synthetic line and continuum intensities that can be compared directly with those observed. We find that filaments have a characteristic width of ${\sim }0.1 \, {\rm pc}$, both on maps of their true surface density and on maps of their $850\, {\rm \mu m}$ dust continuum emission in agreement with previous work. On maps of line emission from CO isotopologues, the apparent widths of filaments are typically several times larger because the line intensities are poorly correlated with the surface density. On maps of line emission from dense gas tracers such as N2H+ and HCN, the apparent widths of filaments are ${\la}0.1\, {\rm pc}$. Thus, current observations of molecular-line emission are compatible with the universal $0.1 \, {\rm pc}$ filament width inferred from Herschel observations, provided proper account is taken of abundance, optical depth, and excitation considerations. We find evidence for ${\sim}0.4 \, {\rm km \, s^{-1}}$ radial velocity differences across filaments. These radial velocity differences might be a useful indicator of the mechanism by which a filament has formed or is forming, for example the turbulent cloud scenario modelled here, as against other mechanisms such as cloud–cloud collisions.

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Water maser and radio continuum emission towards IRAS 23139+5939

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307012896 ◽

2007 ◽

Vol 3 (S242) ◽

pp. 180-181

Author(s):

M. A. Trinidad ◽

S. Curiel ◽

J. M. Torrelles ◽

L. F. Rodríguez ◽

V. Migenes ◽

...

Keyword(s):

Flux Density ◽

Line Emission ◽

The Other ◽

Radio Continuum ◽

High Mass ◽

Continuum Emission ◽

Maser Line ◽

Water Masers ◽

Water Maser ◽

The Continuum

AbstractWe present simultaneous observations of continuum (3.5 and 1.3cm) and water maser line emission (1.3cm) carried out with the VLA-A toward the high-mass object IRAS 23139+5939. We detected two radio continuum sources at 3.5cm separated by 0”5 (~2400 AU), I23139 and I23139S. Based on the observed continuum flux density and the spectral index, we suggest that I23139 is a thermal radio jet associated with a high-mass YSO. On the other hand, based on the spatio-kinematical distribution of the water masers, together with the continuum emission information, we speculate that I23139S is also a jet source powering some of the masers detected in the region.

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Exploring the dust ring in the circum-binary disc around GG Tau A

10.5194/epsc2021-831 ◽

2021 ◽

Author(s):

Claudia Toci ◽

Simone Ceppi ◽

Nicolas Cuello ◽

Giuseppe Lodato ◽

Cristiano Longarini ◽

...

Keyword(s):

Binary Systems ◽

Planet Formation ◽

Initial Conditions ◽

Scattered Light ◽

Complex Structure ◽

Semimajor Axis ◽

Continuum Emission ◽

Orbital Parameter ◽

Semi Major Axis ◽

Multiple Systems

Binaries and multiple systems are common among young stars (Reipurth et al. 2014). These stars are often surrounded by discs of gas and dust, formed due to the conservation of angular momentum of the collapsing cloud, thought to be the site of planet formation. In the case of binary systems, three discs can form: an outer disc surrounding all the stars (called circumbinary disc), and two inner discs around the stars. As circumbinary planets have recently been discovered by Kepler (see e.g., Martin 2018, Bonavita & Desidera 2020), it is crucial to understand the dynamics and evolution of circumbinary discs to better understand the initial conditions of planet formation in multiple systems. The GG Tau A system is an example of a young multiple T Tauri star. The binary is surrounded by a bright disc, observed in the continuum emission at different wavelengths (see e.g., Guilloteau et al. 1999; Dutrey et al. 2014; Phuong et al. 2020b) and in scattered light (e.g., Duchene et al. 2014, Keppler et al. 2020). The disc extends in the dust from 180 to 280 au from the center of mass, and in the gas up to 850 au. The inner (<180 au) part is depleted in gas and dust. Scattered light images show a complex structure in the inner part of the disc, with arcs and filamentary structures connecting the outer ring with the arcs and three shadows. Two different configurations are possible fitting the proper motion data for the system: a co-planar case with a low eccentricity binary with a semi-major axis of 34 au, explored by Cazzoletti et al. 2017 and Keppler et al. 2020, and a misaligned case (i=30) with an eccentric binary (e=0.45) and a wider semimajor axis of 60 au (Aly et al.2018). At the state of the art, all these analyses focused on the gas dynamics only. We will show the results of new 3D SPH simulations of dust and gas performed with the code PHANTOM, devised to test the two possible scenarios. We will describe the dynamics of the system in the two cases, comparing our models with observational results in order to better constraint the orbital parameter of the GG Tau A system. Our predictions will guide future observing campaigns and shed light on the complex evolution of discs in triple stellar systems. &#160;

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Molecular line emission in NGC 1068 imaged with ALMA

Astronomy and Astrophysics ◽

10.1051/0004-6361/201424116 ◽

2014 ◽

Vol 570 ◽

pp. A28 ◽

Cited By ~ 69

Author(s):

S. Viti ◽

S. García-Burillo ◽

A. Fuente ◽

L. K. Hunt ◽

A. Usero ◽

...

Keyword(s):

Line Emission ◽

Molecular Line ◽

Ngc 1068

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Submillimeter line emission from LMC 30 Doradus: The impact of a starburst on a low-metallicity environment

Astronomy and Astrophysics ◽

10.1051/0004-6361/201118321 ◽

2012 ◽

Vol 544 ◽

pp. A84 ◽

Cited By ~ 17

Author(s):

J. L. Pineda ◽

N. Mizuno ◽

M. Röllig ◽

J. Stutzki ◽

C. Kramer ◽

...

Keyword(s):

Line Emission ◽

Low Metallicity ◽

The Impact ◽

30 Doradus

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Understanding biases in measurements of molecular cloud kinematics using line emission

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2432 ◽

2020 ◽

Vol 498 (2) ◽

pp. 2440-2455

Author(s):

Yuxuan (宇轩) Yuan (原) ◽

Mark R Krumholz ◽

Blakesley Burkhart

Keyword(s):

Magnetic Field ◽

Molecular Cloud ◽

Molecular Clouds ◽

Velocity Dispersion ◽

Signal To Noise Ratio ◽

Line Emission ◽

Molecular Line ◽

Velocity Dispersions ◽

Cloud Kinematics ◽

Measurement Biases

ABSTRACT Molecular line observations using a variety of tracers are often used to investigate the kinematic structure of molecular clouds. However, measurements of cloud velocity dispersions with different lines, even in the same region, often yield inconsistent results. The reasons for this disagreement are not entirely clear, since molecular line observations are subject to a number of biases. In this paper, we untangle and investigate various factors that drive linewidth measurement biases by constructing synthetic position–position–velocity cubes for a variety of tracers from a suite of self-gravitating magnetohydrodynamic simulations of molecular clouds. We compare linewidths derived from synthetic observations of these data cubes to the true values in the simulations. We find that differences in linewidth as measured by different tracers are driven by a combination of density-dependent excitation, whereby tracers that are sensitive to higher densities sample smaller regions with smaller velocity dispersions, opacity broadening, especially for highly optically thick tracers such as CO, and finite resolution and sensitivity, which suppress the wings of emission lines. We find that, at fixed signal-to-noise ratio, three commonly used tracers, the J = 4 → 3 line of CO, the J = 1 → 0 line of C18O, and the (1,1) inversion transition of NH3, generally offer the best compromise between these competing biases, and produce estimates of the velocity dispersion that reflect the true kinematics of a molecular cloud to an accuracy of $\approx 10{{\ \rm per\ cent}}$ regardless of the cloud magnetic field strengths, evolutionary state, or orientations of the line of sight relative to the magnetic field. Tracers excited primarily in gas denser than that traced by NH3 tend to underestimate the true velocity dispersion by $\approx 20{{\ \rm per\ cent}}$ on average, while low-density tracers that are highly optically thick tend to have biases of comparable size in the opposite direction.

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