The large crescents imaged by ALMA in transition discs suggest that azimuthal dust trapping concentrates the larger grains, but centimetre-wavelengths continuum observations are required to map the ...distribution of the largest observable grains. A previous detection at ∼1 cm of an unresolved clump along the outer ring of MWC 758 (Clump 1), and buried inside more extended sub-mm continuum, motivates followup VLA observations. Deep multiconfiguration integrations reveal the morphology of Clump 1 and additional cm-wave components that we characterize via comparison with a deconvolution of recent 342 GHz data (∼1 mm). Clump 1, which concentrates ∼1/3 of the whole disc flux density at ∼1 cm, is resolved as a narrow arc with a deprojected aspect ratio χ > 5.6, and with half the azimuthal width than at 342 GHz. The spectral trends in the morphology of Clump 1 are quantitatively consistent with the Lyra-Lin prescriptions for dust trapping in an anticyclonic vortex, provided with porous grains (f ∼ 0.2 ± 0.2) in a very elongated (χ ∼ 14 ± 3) and cold (T∼ 23± 2 K) vortex. The same prescriptions constrain the turbulence parameter α and the gas surface density Σ g through log _{10}(α × Σ _g / g cm^{-2} ) ∼ -2.3± 0.4, thus requiring values for Σ g larger than a factor of a few compared to that reported in the literature from the CO isotopologues, if α ≲ 10 -3 . Such physical conditions imply an appreciably optically thick continuum even at cm-wavelengths (τ_{33 GHz}∼ 0.2). A secondary and shallower peak at 342 GHz is about twice fainter relative to Clump 1 at 33 GHz. Clump 2 appears to be less efficient at trapping large grains.
Abstract The discovery of protoplanets and circumplanetary disks provides a unique opportunity to characterize planet formation through observations. Massive protoplanets shape the physical and ...chemical structure of their host circumstellar disk by accretion, localized emission, and disk depletion. In this work, we study the thermal changes induced within the disk by protoplanet accretion and synthetic predictions through hydrodynamical simulations with postprocessed radiative transfer with an emphasis on radio millimeter emission. We explored distinct growth conditions and varied both planetary accretion rates and the local dust-to-gas mass ratios for a protoplanet at 1200 K. The radiative transfer models show that beyond the effect of disk gaps, in most cases, the circumplanetary disk (CPD) and the planet’s emission locally increase the disk temperature. Moreover, depending on the local dust-to-gas depletion and accretion rate, the presence of the CPD may have detectable signatures in millimeter emission. It also has the power to generate azimuthal asymmetries that are important for continuum subtraction. Thus, if other means of detection of protoplanets are proven, the lack of corresponding evidence at other wavelengths can set limits on their growth timescales through a combined analysis of the local dust-to-gas ratio and the accretion rate.
FOUR SEASONS HOUSE Alarcón, Felipe
ARQ (Santiago, Chile),
04/2023, Letnik:
113
Journal Article
Recenzirano
Every renovation project makes use of embodied energy, increasing the energy and material footprint of a building in the short term. But by reusing the longerlasting layer of structure, renovations ...can lower the environmental cost of architecture in the long term: a building can be retrofitted with energy-efficient solutions and more socially effective spaces. Felipe Alarcón's renovation demonstrates this principle, improving the energy performance of the house while allowing the architect to rethink its forms of domesticity, relationship to the site and its neighborhood.
Abstract Upcoming new coronographs with deeper contrast limits, together with planned and current high-contrast imaging campaigns, will push the detectability limit of protoplanets. These ...planet-hunting campaigns present a new opportunity to characterize protoplanets and their surrounding environments. However, there are clear uncertainties as to what the extinction levels are at different regions of protoplanetary disks, which will impede our ability to characterize young planets. A correct understanding of the expected extinction, together with multiple photometric observations, will lead to constraints on the extinction levels, dust growth, disk evolution, and protoplanetary accretion rates. In this work, we used hydrodynamic simulations and protoplanetary disk observational constraints obtained from both dust and gas emission to explore the expected extinction maps for continuum filters associated with strong hydrogen lines as tracers of accretion and key broadband photometric filters. We provide a scaling relationship for the extinction as a function of planetary separation and disk mass for three different gas giant masses. We also report values for a subset of disks of interest targeted by multiple imaging campaigns. The described values will be useful for the optimal design of future planet-hunting surveys and for giving context to nondetections in protoplanetary disks and the observed fluxes of point sources along with the birth conditions of protoplanets.
Abstract
Here we aim to explore the origin of the strong C
2
H lines to reimagine the chemistry of protoplanetary disks. There are a few key aspects that drive our analysis. First, C
2
H is detected ...in young and old systems, hinting at a long-lived chemistry. Second, as a radical, C
2
H is rapidly destroyed, within <1000 yr. These two statements hint that the chemistry responsible for C
2
H emission must be predominantly in the gas phase and must be in equilibrium. Combining new and published chemical models, we find that elevating the total volatile (gas and ice) C/O ratio is the only natural way to create a long-lived, high C
2
H abundance. Most of the C
2
H resides in gas with an
F
UV
/
n
gas
∼ 10
−7
G
0
cm
3
. To elevate the volatile C/O ratio, additional carbon has to be released into the gas to enable equilibrium chemistry under oxygen-poor conditions. Photoablation of carbon-rich grains seems the most straightforward way to elevate the C/O ratio above 1.5, powering a long-lived equilibrium cycle. The regions at which the conditions are optimal for the presence of high C/O ratio and elevated C
2
H abundances in the gas disk set by the
F
UV
/
n
gas
condition lie just outside the pebble disk as well as possibly in disk gaps. This process can thus also explain the (hints of) structure seen in C
2
H observations.
Todo proyecto de renovación hace uso de energía contenida, aumentando la huella energética y material de una obra en el corto plazo. Pero reutilizando la estructura -su capa más longeva- las ...renovaciones pueden disminuir el costo medioambiental de la arquitectura al largo plazo: un edificio puede reequiparse con soluciones energéticamente eficientes y espacios más socialmente efectivos. La remodelación de Felipe Alarcón demuestra este principio, mejorando el rendimiento energético de la vivienda, al tiempo que permite al arquitecto replantear sus formas de domesticidad, relación con el sitio y su vecindario.
Recent surveys of protoplanetary disks show that substructure in dust thermal continuum emission maps is common in protoplanetary disks. These substructures, most prominently rings and gaps, shape ...and change the chemical and physical conditions of the disk, along with the dust size distributions. In this work, we use a thermochemical code to focus on the chemical evolution that is occurring within the gas-depleted gap and the dust-rich ring often observed behind it. The compositions of these spatial locations are of great import, as the gas and ice-coated grains will end up being part of the atmospheres of gas giants and/or the seeds of rocky planets. Our models show that the dust temperature at the midplane of the gap increases, enough to produce local sublimation of key volatiles and pushing the molecular layer closer to the midplane, while it decreases in the dust-rich ring, causing a higher volatile deposition onto the dust grain surfaces. Further, the ring itself presents a freeze-out trap for volatiles in local flows powered by forming planets, becoming a site of localized volatile enhancement. Within the gas-depleted gap, the line emission depends on several different parameters, such as the depth of the gap in surface density, the location of the dust substructure, and the abundance of common gas tracers, such as CO. In order to break this uncertainty between abundance and surface density, other methods, such as disk kinematics, become necessary to constrain the disk structure and its chemical evolution.
ABSTRACT
FU Orionis-type objects (FUors) are embedded protostars that undergo episodes of high accretion, potentially indicating a widespread but poorly understood phase in the formation of low-mass ...stars. Gaining a better understanding of the influence exerted by these outbursts on the evolution of the surrounding protoplanetary disc may hold significant implications for the process of planet formation and the evolution of disc chemistry. The heating due to outbursts of high accretion in FUors pushes the snowlines of key volatiles farther out in the disc, so they become easier to observe and study. Among the known FUors, V883 Ori is of particular interest. V883 Ori was the first FUor to show indirect evidence of a resolvable snowline beyond 40 au. By introducing a radial-dependent model of this source including viscous heating, we show that active heating is needed to reproduce the steep thermal profile of dust in the inner disc of V883 Ori. Our disc modelling combines the effect of stellar irradiation and the influence on the disc shape caused by the outburst of accretion. The accuracy of our model is tested by comparing synthetic Atacama Larga Millimeter Array images with continuum observations of V883 Ori, showing that the model successfully reproduces the 1.3 mm emission of V883 Ori at high spatial resolution. Our final predictions underline the importance of viscous heating as a predominant heat source for this type of object, changing the physical conditions (shape and temperature) of the disc, and influencing its evolution.
Abstract
Over the past 5 yr, studies of the kinematics in protoplanetary disks have led to the discovery of new protoplanet candidates and several structures linked to possible planet−disk ...interactions. We detect a localized kinematic bipolar structure in the HD 163296 disk present inside the deepest dust gap at 48 au from atomic carbon line emission. HD 163296's stellar jet and molecular winds have been described in detail in the literature; however, the kinematic anomaly in C
i
emission is not associated with either of them. Further, the velocity of the kinematic structure points indicates a component fast enough to differentiate it from the Keplerian profile of the disk, and its atomic nature hints at a localized UV source strong enough to dissociate CO and launch a C
i
outflow or a strong polar flow from the upper layers of the disk. By discarding the stellar jet and previously observed molecular winds, we explore different sources for this kinematic feature in C
i
emission that could be associated with a protoplanet inflow/outflow or disk winds.
An inner warp in the DoAr 44 T Tauri transition disc Casassus, Simon; Avenhaus, Henning; Pérez, Sebastián ...
Monthly notices of the Royal Astronomical Society,
07/2018, Letnik:
477, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
Optical/IR images of transition discs (TDs) have revealed deep intensity decrements in the rings of HAeBes HD 142527 and HD 100453 that can be interpreted as shadowing from sharply tilted ...inner discs, such that the outer discs are directly exposed to stellar light. Here we report similar dips in SPHERE+IRDIS differential polarized imaging (DPI) of T Tauri DoAr 44. With a fairly axially symmetric ring in the sub-mm radio continuum, DoAr 44 is likely also a warped system. We constrain the warp geometry by comparing radiative transfer predictions with the DPI data in H band (Qϕ(H)) and with a re-processing of archival 336 GHz ALMA observations. The observed DPI shadows have coincident radio counterparts, but the intensity drops are much deeper in Qϕ(H) (∼88 per cent), compared to the shallow drops at 336 GHz (∼24 per cent). Radiative transfer predictions with an inner disc tilt of ∼30 ± 5 deg approximately account for the observations. ALMA long-baseline observations should allow the observation of the warped gas kinematics inside the cavity of DoAr 44.
PDF
