scholarly journals Constraining the radial drift of millimeter-sized grains in the protoplanetary disks in Lupus

2020 ◽  
Vol 638 ◽  
pp. A38 ◽  
Author(s):  
L. Trapman ◽  
M. Ansdell ◽  
M. R. Hogerheijde ◽  
S. Facchini ◽  
C. F. Manara ◽  
...  
Keyword(s):  
Grain Growth ◽  
Optical Depth ◽  
Thermal Emission ◽  
Signal To Noise Ratio ◽  
Protoplanetary Disks ◽  
Outer Radius ◽  
Size Difference ◽  
Star Forming ◽  
Dust Evolution ◽  
Depth Effects

Context. Recent ALMA surveys of protoplanetary disks have shown that for most disks the extent of the gas emission is greater than the extent of the thermal emission of millimeter-sized dust. Both line optical depth and the combined effect of radially dependent grain growth and radial drift may contribute to this observed effect. To determine whether or not radial drift is common across the disk population, quantitative estimates of the effect of line optical depth are required. Aims. For a sample of ten disks from the Lupus survey we investigate how well dust-based models without radial dust evolution reproduce the observed 12CO outer radius, and determine whether radial dust evolution is required to match the observed gas–dust size difference. Methods. Based on surface density profiles derived from continuum observations we used the thermochemical code DALI to obtain 12CO synthetic emission maps. Gas and dust outer radii of the models were calculated using the same methods as applied to the observations. The gas and dust outer radii (RCO, Rmm) calculated using only line optical depth were compared to observations on a source-by-source basis. Results. For five disks, we find RCO, obs∕Rmm, obs > RCO, mdl∕Rmm, mdl. For these disks we need both dust evolution and optical depth effects to explain the observed gas–dust size difference. For the other five disks, the observed RCO∕Rmm lies within the uncertainties on RCO, mdl∕Rmm, mdl due to noise. For these disks the observed gas–dust size difference can be explained using only line optical depth effects. We also identify six disks not included in our initial sample but part of a survey of the same star-forming region that show significant signal-to-noise ratio (S∕N ≥ 3) 12CO J = 2−1 emission beyond 4 × Rmm. These disks, for which no RCO is available, likely have RCO∕Rmm ≫ 4 and are difficult to explain without substantial dust evolution. Conclusions. Most of the disks in our sample of predominantly bright disks are consistent with radial drift and grain growth. We also find six faint disks where the observed gas–dust size difference hints at considerable radial drift and grain growth, suggesting that these are common features among both bright and faint disks. The effects of radial drift and grain growth can be observed in disks where the dust and gas radii are significantly different, while more detailed models and deeper observations are needed to see this effect in disks with smaller differences.

scholarly journals Gas versus dust sizes of protoplanetary discs: effects of dust evolution

2019 ◽  
Vol 629 ◽  
pp. A79 ◽  
Author(s):  
L. Trapman ◽  
S. Facchini ◽  
M. R. Hogerheijde ◽  
E. F. van Dishoeck ◽  
S. Bruderer
Keyword(s):  
Grain Growth ◽  
Optical Depth ◽  
Outer Radius ◽  
Size Difference ◽  
Clear Sign ◽  
Thermochemical Model ◽  
High Fraction ◽  
Space Dust ◽  
Dust Evolution ◽  
Protoplanetary Discs

Context. The extent of the gas in protoplanetary discs is observed to be universally larger than the extent of the dust. This is often attributed to radial drift and grain growth of the millimetre grains, but line optical depth produces a similar observational signature. Aims. We investigate in which parts of the disc structure parameter space dust evolution and line optical depth are the dominant drivers of the observed gas and dust size difference. Methods. Using the thermochemical model DALI with dust evolution included we ran a grid of models aimed at reproducing the observed gas and dust size dichotomy. Results. The relation between Rdust and dust evolution is non-monotonic and depends on the disc structure. The quantity Rgas is directly related to the radius where the CO column density drops below 1015 cm−2 and CO becomes photodissociated; Rgas is not affected by dust evolution but scales with the total CO content of the disc. While these cases are rare in current observations, Rgas/Rdust > 4 is a clear sign of dust evolution and radial drift in discs. For discs with a smaller Rgas/Rdust, identifying dust evolution from Rgas/Rdust requires modelling the disc structure including the total CO content. To minimize the uncertainties due to observational factors requires FWHMbeam < 1× the characteristic radius and a peak S/N > 10 on the 12CO emission moment zero map. For the dust outer radius to enclose most of the disc mass, it should be defined using a high fraction (90–95%) of the total flux. For the gas, any radius enclosing >60% of the 12CO flux contains most of the disc mass. Conclusions. To distinguish radial drift and grain growth from line optical depth effects based on size ratios requires discs to be observed at high enough angular resolution and the disc structure should to be modelled to account for the total CO content of the disc.

Gas extent in protoplanetary disks of the Lupus star forming region

2020 ◽  
Author(s):  
Enrique Sanchis
Keyword(s):  
Protoplanetary Disks ◽  
Stellar Mass ◽  
Size Ratio ◽  
Gas Content ◽  
Continuum Emission ◽  
Size Difference ◽  
Formation Mechanisms ◽  
Star Forming ◽  
Dust Disk ◽  
Dust Evolution

&lt;p&gt;I will present a demographic study of the gas content in protoplanetary disks of the Lupus star-forming region, based on the previous ALMA surveys of the region.&lt;/p&gt; &lt;p&gt;Planets form around stars during their pre-main sequence phase, when still surrounded by a circumstellar disk of dust and gas. Setting observational constraints on the gas and dust properties of protoplanetary disks is crucial in order to understand what are the ongoing physical processes in the disk. These processes shape the planet formation mechanisms, and ultimately tell us about the disk&amp;#8217;s ability to form planets.&lt;/p&gt; &lt;p&gt;The advent of ALMA allowed us to characterize dust properties in large populations of disks in several star-forming regions. Nevertheless, demographic studies of the gas content in these disk populations are scarce and generally incomplete, due to the fewer detections, and other difficulties when studying gas content.&lt;/p&gt; &lt;p&gt;In this work, we were able to assemble a large and homogeneous sample of disks from the Lupus region, all detected in &lt;sup&gt;12&lt;/sup&gt;CO and dust continuum. Gas emission profiles and sizes are estimated on 43 disks of the Lupus region. The profiles are inferred from the integrated emission maps of the &lt;sup&gt;12&lt;/sup&gt;CO transition line in ALMA Band 6. The observed emission is modeled using empirical functions: either the Nuker profile or an elliptical Gaussian for more compact sources. The gas size, defined as a certain fraction (e.g. 68%) of the total flux, is inferred from the modeled emission profiles.&lt;/p&gt; &lt;p&gt;These gas properties are then compared to the dust properties of the same objects, estimated from ALMA surveys in Band 7 and using analogous methodology.&lt;/p&gt; &lt;p&gt;The relative size of gas and dust is a key diagnostic of dust evolution. Large dust grains are decoupled from gas and drift inwards. Thus, if dust growth is prominent in these disks, the detected dust continuum emission in sub-mm wavelengths are expected to be several times smaller than the gas extent.&lt;/p&gt; &lt;p&gt;The results of our extensive sample confirm the larger gas size when compared to the dust size. The gas disk size is on average 2.6 times larger than the dust disk. This size difference can be explained by effective drifting of dust, but also by the optical depth difference between &lt;sup&gt;12&lt;/sup&gt;CO and dust continuum. Disentangling between these two effects is in general difficult; only large size ratios (typically beyond 4) unequivocally exhibit prominent dust evolution.&lt;/p&gt; &lt;p&gt;Only a small fraction (~18%) of the disk population has a size ratio larger than 4. Radial drift is intimately linked to grain growth, both are crucial processes to form the cores of planets. Our results might suggest that dust evolution is less common than previously thought.&lt;/p&gt; &lt;p&gt;We also investigated possible trends of the size ratio with stellar and disk properties, e.g. stellar mass, disk mass, integrated CO flux; no clear correlation can be found. Interestingly, the only Brown Dwarf of the sample with characterized gas and dust disk sizes shows a relatively large ratio of 3.8. On the other stellar mass range end, disks around stars with mass &gt; 0.8 M&lt;sub&gt;sun&lt;/sub&gt; have a tentative lower ratio of 2.1. Larger samples in the low mass regime and in the rest of stellar mass ranges are needed in order to discern possible trends between spectral types or other properties of the host stars.&lt;/p&gt;

scholarly journals Observational constraints on dust disk sizes in tidally truncated protoplanetary disks in multiple systems in the Taurus region

2019 ◽  
Vol 628 ◽  
pp. A95 ◽  
Author(s):  
C. F. Manara ◽  
M. Tazzari ◽  
F. Long ◽  
G. J. Herczeg ◽  
G. Lodato ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Protoplanetary Disks ◽  
Mass Range ◽  
Outer Radius ◽  
Continuum Emission ◽  
Stellar Systems ◽  
Multiple Systems ◽  
Star Forming ◽  
Dust Disk ◽  
The Impact

The impact of stellar multiplicity on the evolution of planet-forming disks is still the subject of debate. Here we present and analyze disk structures around ten multiple stellar systems that were included in an unbiased, high spatial resolution survey performed with ALMA of 32 protoplanetary disks in the Taurus star-forming region. At the unprecedented spatial resolution of ~0.12′′ we detect and spatially resolve the disks around all primary stars, and those around eight secondary and one tertiary star. The dust radii of disks around multiple stellar systems are smaller than those around single stars in the same stellar mass range and in the same region. The disks in multiple stellar systems also show a steeper decay of the millimeter continuum emission at the outer radius than disks around single stars, suggestive of the impact of tidal truncation on the shape of the disks in multiple systems. However, the observed ratio between the dust disk radii and the observed separation of the stars in the multiple systems is consistent with analytic predictions of the effect of tidal truncation only if the eccentricities of the binaries are rather high (typically >0.5) or if the observed dust radii are a factor of two smaller than the gas radii, as is typical for isolated systems. Similar high-resolution studies targeting the gaseous emission from disks in multiple stellar systems are required to resolve this question.

scholarly journals Hints on the origins of particle traps in protoplanetary disks given by the Mdust – M⋆ relation

2020 ◽  
Vol 635 ◽  
pp. A105 ◽  
Author(s):  
Paola Pinilla ◽  
Ilaria Pascucci ◽  
Sebastian Marino
Keyword(s):  
Giant Planet ◽  
Protoplanetary Disks ◽  
Stellar Mass ◽  
Dust Particles ◽  
Low Mass Stars ◽  
Dust Trapping ◽  
Star Forming ◽  
Star Forming Regions ◽  
Demographic Surveys ◽  
Dust Evolution

Context. Demographic surveys of protoplanetary disks, carried out mainly with the Atacama Large Millimeter/submillimete Array, have provided access to a large range of disk dust masses (Mdust) around stars with different stellar types and in different star-forming regions. These surveys found a power-law relation between Mdust and M⋆ that steepens in time, but which is also flatter for transition disks (TDs). Aims. We aim to study the effect of dust evolution in the Mdust−M⋆ relation. In particular, we are interested in investigating the effect of particle traps on this relation. Methods. We performed dust evolution models, which included perturbations to the gas surface density with different amplitudes to investigate the effect of particle trapping on the Mdust−M⋆ relation. These perturbations were aimed at mimicking pressure bumps that originated from planets. We focused on the effect caused by different stellar and disk masses based on exoplanet statistics that demonstrate a dependence of planet mass on stellar mass and metallicity. Results. Models of dust evolution can reproduce the observed Mdust−M⋆ relation in different star-forming regions when strong pressure bumps are included and when the disk mass scales with stellar mass (case of Mdisk = 0.05 M⋆ in our models). This result arises from dust trapping and dust growth beyond centimeter-sized grains inside pressure bumps. However, the flatter relation of Mdust − M⋆ for TDs and disks with substructures cannot be reproduced by the models unless the formation of boulders is inhibited inside pressure bumps. Conclusions. In the context of pressure bumps originating from planets, our results agree with current exoplanet statistics on giant planet occurrence increasing with stellar mass, but we cannot draw a conclusion about the type of planets needed in the case of low-mass stars. This is attributed to the fact that for M⋆ < 1 M⊙, the observed Mdust obtained from models is very low due to the efficient growth of dust particles beyond centimeter-sizes inside pressure bumps.

scholarly journals [C II] 158 μm self-absorption and optical depth effects

2020 ◽  
Vol 636 ◽  
pp. A16 ◽  
Author(s):  
C. Guevara ◽  
J. Stutzki ◽  
V. Ossenkopf-Okada ◽  
R. Simon ◽  
J. P. Pérez-Beaupuits ◽  
...  
Keyword(s):  
Optical Depth ◽  
Column Density ◽  
Signal To Noise Ratio ◽  
Far Infrared ◽  
Emission Lines ◽  
High Spectral Resolution ◽  
Line Of Sight ◽  
High Signal ◽  
Line Profiles ◽  
Star Forming

Context. The [C II] 158 μm far-infrared fine-structure line is one of the most important cooling lines of the star-forming interstellar medium (ISM). It is used as a tracer of star formation efficiency in external galaxies and to study feedback effects in parental clouds. High spectral resolution observations have shown complex structures in the line profiles of the [C II] emission. Aims. Our aim is to determine whether the complex profiles observed in [12C II] are due to individual velocity components along the line-of-sight or to self-absorption based on a comparison of the [12C II] and isotopic [13C II] line profiles. Methods. Deep integrations with the SOFIA/upGREAT 7-pixel array receiver in the sources of M43, Horsehead PDR, Monoceros R2, and M17 SW allow for the detection of optically thin [13C II] emission lines, along with the [12C II] emission lines, with a high signal-to-noise ratio. We first derived the [12C II] optical depth and the [C II] column density from a single component model. However, the complex line profiles observed require a double layer model with an emitting background and an absorbing foreground. A multi-component velocity fit allows us to derive the physical conditions of the [C II] gas: column density and excitation temperature. Results. We find moderate to high [12C II] optical depths in all four sources and self-absorption of [12C II] in Mon R2 and M17 SW. The high column density of the warm background emission corresponds to an equivalent Av of up to 41 mag. The foreground absorption requires substantial column densities of cold and dense [C II] gas, with an equivalent Av ranging up to about 13 mag. Conclusions. The column density of the warm background material requires multiple photon-dominated region surfaces stacked along the line of sight and in velocity. The substantial column density of dense and cold foreground [C II] gas detected in absorption cannot be explained with any known scenario and we can only speculate on its origins.

scholarly journals DUST PROCESSING AND GRAIN GROWTH IN PROTOPLANETARY DISKS IN THE TAURUS-AURIGA STAR-FORMING REGION

2009 ◽  
Vol 182 (2) ◽  
pp. 477-508 ◽  
Author(s):  
B. A. Sargent ◽  
W. J. Forrest ◽  
C. Tayrien ◽  
M. K. McClure ◽  
Dan M. Watson ◽  
...  
Keyword(s):  
Grain Growth ◽  
Protoplanetary Disks ◽  
Star Forming

scholarly journals A NIKA view of two star-forming infrared dark clouds: Dust emissivity variations and mass concentration

2018 ◽  
Vol 615 ◽  
pp. A18 ◽  
Author(s):  
A. J. Rigby ◽  
N. Peretto ◽  
R. Adam ◽  
P. Ade ◽  
P. André ◽  
...  
Keyword(s):  
Star Formation ◽  
Mass Concentration ◽  
Thermal Emission ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Interstellar Clouds ◽  
Star Forming ◽  
Dark Clouds ◽  
Construct Maps ◽  
Infrared Dark Clouds

Context. The thermal emission of dust grains is a powerful tool for probing cold, dense regions of molecular gas in the interstellar medium, and so constraining dust properties is key to obtaining accurate measurements of dust mass and temperature. Aims. By placing constraints on the dust emissivity spectral index, β, towards two star-forming infrared dark clouds – SDC18.888–0.476 and SDC24.489–0.689 – we aim to evaluate the role of mass concentration in the associated star-formation activity. Methods. We exploited the simultaneous 1.2 and 2.0 mm imaging capability of the NIKA camera on the IRAM 30 m telescope to construct maps of β for both clouds, and by incorporating Herschel observations, we created H2 column density maps with 13′′ angular resolution. Results. While we find no significant systematic radial variations around the most massive clumps in either cloud on ≳0.1 pc scales, their mean β values are significantly different, with β̅ = 2.07 ± 0.09 (random) ± 0.25 (systematic) for SDC18.888–0.476 and β̅ = 1.71 ± 0.09 (random) ± 0.25 (systematic) for SDC24.489–0.689. These differences could be a consequence of the very different environments in which both clouds lie, and we suggest that the proximity of SDC18.888–0.476 to the W39 H II region may raise β on scales of ~1 pc. We also find that the mass in SDC24.489–0.689 is more centrally concentrated and circularly symmetric than in SDC18.888–0.476, and is consistent with a scenario in which spherical globally-collapsing clouds concentrate a higher fraction of their mass into a single core than elongated clouds that will more easily fragment, distributing their mass into many cores. Conclusions. We demonstrate that β variations towards interstellar clouds can be robustly constrained with high signal-to-noise ratio (S/N) NIKA observations, providing more accurate estimates of their masses. The methods presented here will be applied to the Galactic Star Formation with NIKA2 (GASTON) guaranteed time large programme, extending our analysis to a statistically significant sample of star-forming clouds.

scholarly journals Testing the accuracy of reflection-based supermassive black hole spin measurements in AGN

2018 ◽  
Vol 614 ◽  
pp. A44 ◽  
Author(s):  
E. S. Kammoun ◽  
E. Nardini ◽  
G. Risaliti
Keyword(s):  
Thermal Emission ◽  
Signal To Noise Ratio ◽  
Galactic Nuclei ◽  
Relativistic Effects ◽  
High Signal ◽  
X Ray ◽  
Multiple Components ◽  
Spin Parameter ◽  
Partial Covering ◽  
Spin Measurements

Context. X-ray reflection is a very powerful method to assess the spin of supermassive black holes (SMBHs) in active galactic nuclei (AGN), yet this technique is not universally accepted. Indeed, complex reprocessing (absorption, scattering) of the intrinsic spectra along the line of sight can mimic the relativistic effects on which the spin measure is based. Aims. In this work, we test the reliability of SMBH spin measurements that can currently be achieved through the simulations of high-quality XMM-Newton and NuSTAR spectra. Methods. Each member of our group simulated ten spectra with multiple components that are typically seen in AGN, such as warm and (partial-covering) neutral absorbers, relativistic and distant reflection, and thermal emission. The resulting spectra were blindly analysed by the other two members. Results. Out of the 60 fits, 42 turn out to be physically accurate when compared to the input model. The SMBH spin is retrieved with success in 31 cases, some of which (9) are even found among formally inaccurate fits (although with looser constraints). We show that, at the high signal-to-noise ratio assumed in our simulations, neither the complexity of the multi-layer, partial-covering absorber nor the input value of the spin are the major drivers of our results. The height of the X-ray source (in a lamp-post geometry) instead plays a crucial role in recovering the spin. In particular, a success rate of 16 out of 16 is found among the accurate fits for a dimensionless spin parameter larger than 0.8 and a lamp-post height lower than five gravitational radii.

scholarly journals Hemispherical variance anomaly and reionization optical depth

2020 ◽  
Vol 499 (3) ◽  
pp. 3563-3570
Author(s):  
Márcio O’Dwyer ◽  
Craig J Copi ◽  
Johanna M Nagy ◽  
C Barth Netterfield ◽  
John Ruhl ◽  
...  
Keyword(s):  
Optical Depth ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Signal To Noise Ratio ◽  
Cosmological Parameters ◽  
Temperature Data ◽  
Microwave Background ◽  
Parameter Uncertainties ◽  
Polarization Data ◽  
Best Fitting

ABSTRACT Cosmic microwave background (CMB) full-sky temperature data show a hemispherical asymmetry in power nearly aligned with the Ecliptic, with the Northern hemisphere displaying an anomalously low variance, while the Southern hemisphere appears consistent with expectations from the best-fitting theory, Lambda Cold Dark Matter (ΛCDM). The low signal-to-noise ratio in current polarization data prevents a similar comparison. Polarization realizations constrained by temperature data show that in ΛCDM the lack of variance is not expected to be present in polarization data. Therefore, a natural way of testing whether the temperature result is a fluke is to measure the variance of CMB polarization components. In anticipation of future CMB experiments that will allow for high-precision large-scale polarization measurements, we study how the variance of polarization depends on ΛCDM-parameter uncertainties by forecasting polarization maps with Planck’s Markov chain Monte Carlo chains. We show that polarization variance is sensitive to present uncertainties in cosmological parameters, mainly due to current poor constraints on the reionization optical depth τ, which drives variance at low multipoles. We demonstrate how the improvement in the τ measurement seen between Planck’s two latest data releases results in a tighter constraint on polarization variance expectations. Finally, we consider even smaller uncertainties on τ and how more precise measurements of τ can drive the expectation for polarization variance in a hemisphere close to that of the cosmic-variance-limited distribution.

scholarly journals ATLASGAL – Ammonia observations towards the southern Galactic plane

2018 ◽  
Vol 609 ◽  
pp. A125 ◽  
Author(s):  
M. Wienen ◽  
F. Wyrowski ◽  
K. M. Menten ◽  
J. S. Urquhart ◽  
C. M. Walmsley ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Hyperfine Structure ◽  
Optical Depth ◽  
Line Width ◽  
Rotational Temperature ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass

Context. The initial conditions of molecular clumps in which high-mass stars form are poorly understood. In particular, a more detailed study of the earliest evolutionary phases is needed. The APEX Telescope Large Area Survey of the whole inner Galactic disk at 870 μm, ATLASGAL, has therefore been conducted to discover high-mass star-forming regions at different evolutionary phases. Aims. We derive properties such as velocities, rotational temperatures, column densities, and abundances of a large sample of southern ATLASGAL clumps in the fourth quadrant. Methods. Using the Parkes telescope, we observed the NH3 (1, 1) to (3, 3) inversion transitions towards 354 dust clumps detected by ATLASGAL within a Galactic longitude range between 300° and 359° and a latitude within ± 1.5°. For a subsample of 289 sources, the N2H+ (1–0) line was measured with the Mopra telescope. Results. We measured a median NH3 (1, 1) line width of ~ 2 km s-1, rotational temperatures from 12 to 28 K with a mean of 18 K, and source-averaged NH3 abundances from 1.6 × 10-6 to 10-8. For a subsample with detected NH3 (2, 2) hyperfine components, we found that the commonly used method to compute the (2, 2) optical depth from the (1, 1) optical depth and the (2, 2) to (1, 1) main beam brightness temperature ratio leads to an underestimation of the rotational temperature and column density. A larger median virial parameter of ~ 1 is determined using the broader N2H+ line width than is estimated from the NH3 line width of ~ 0.5 with a general trend of a decreasing virial parameter with increasing gas mass. We obtain a rising NH3 (1, 1)/N2H+ line-width ratio with increasing rotational temperature. Conclusions. A comparison of NH3 line parameters of ATLASGAL clumps to cores in nearby molecular clouds reveals smaller velocity dispersions in low-mass than high-mass star-forming regions and a warmer surrounding of ATLASGAL clumps than the surrounding of low-mass cores. The NH3 (1, 1) inversion transition of 49% of the sources shows hyperfine structure anomalies. The intensity ratio of the outer hyperfine structure lines with a median of 1.27 ± 0.03 and a standard deviation of 0.45 is significantly higher than 1, while the intensity ratios of the inner satellites with a median of 0.9 ± 0.02 and standard deviation of 0.3 and the sum of the inner and outer hyperfine components with a median of 1.06 ± 0.02 and standard deviation of 0.37 are closer to 1.

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