Young Disk Research Articles

A Search for Companions via Direct Imaging in the DSHARP Planet-forming Disks

Abstract 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 hypothesized 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 the 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 11 (174.9 au) for RU Lup and at 042 (55 au) for Elias 24. In the case of RU Lup, the proper motion of the candidate is consistent with a stationary background contaminant, based on the astrometry derived from our observations and available archival data. For Elias 24 the point-like source candidate is located in one of the disk gaps at 55 au. Assuming that it is a planetary companion, our analysis suggests a mass ranging from 0.5M J up to 5M J, depending on the presence of a circumplanetary disk and its contribution to the luminosity of the system. However, no clear confirmation is obtained at this stage, and follow-up observations are mandatory to verify that the proposed source is physical, comoving with the stellar host, and associated with a young massive planet sculpting the gap observed at 55 au. For all the remaining systems, the lack of detections suggests the presence of planetary companions with masses lower than 5M J, based on our derived mass detection limits. This is consistent with predictions of both hydrodynamical simulations and kinematical signatures on the disk and allows us to set upper limits on the presence of massive planets in these young disks.

Resolved molecular line observations reveal an inherited molecular layer in the young disk around TMC1A

Context.Physical processes that govern the star and planet formation sequence influence the chemical composition and evolution of protoplanetary disks. Recent studies allude to an early start to planet formation already during the formation of a disk. To understand the chemical composition of protoplanets, we need to constrain the composition and structure of the disks from whence they are formed.Aims.We aim to determine the molecular abundance structure of the young disk around the TMC1A protostar on au scales in order to understand its chemical structure and any possible implications for disk formation.Methods.We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of CO, HCO+, HCN, DCN, and SO line emission, as well as dust continuum emission, in the vicinity of TMC1A. Molecular column densities are estimated both under the assumption of optically thin emission from molecules in local thermodynamical equilibrium (LTE) as well as through more detailed non-LTE radiative transfer calculations.Results.Resolved dust continuum emission from the disk is detected between 220 and 260 GHz. Rotational transitions from HCO+, HCN, and SO are also detected from the inner 100 au region. We further report on upper limits to vibrational HCNυ2= 1, DCN, and N2D+lines. The HCO+emission appears to trace both the Keplerian disk and the surrounding infalling rotating envelope. HCN emission peaks toward the outflow cavity region connected with the CO disk wind and toward the red-shifted part of the Keplerian disk. From the derived HCO+abundance, we estimate the ionization fraction of the disk surface, and find values that imply that the accretion process is not driven by the magneto-rotational instability. The molecular abundances averaged over the TMC1A disk are similar to its protostellar envelope and other, older Class II disks. We meanwhile find a discrepancy between the young disk’s molecular abundances relative to Solar System objects.Conclusions.Abundance comparisons between the disk and its surrounding envelope for several molecular species reveal that the bulk of planet-forming material enters the disk unaltered. Differences in HCN and H2O molecular abundances between the disk around TMC1A, Class II disks, and Solar System objects trace the chemical evolution during disk and planet formation.

Determined the Effective Temperature and Gravity Acceleration at the Atmosphere of (HD165908) Star

The study of the chemical composition of stars in our Galaxy showed that it changes in a non-random way from a star to a star: older stars and halo stars have a metal deficit compared to young stars and disc stars. However, this is not always the case. Sometimes old stars have a solar chemical composition, and young stars show a deficit of metals. It is believed that the formed stars has a chemical composition of the interstellar substance from which it was formed; therefore, the initial content of elements in its atmosphere depends on the time and place of birth. Within the framework of this work, echelle spectra of star 99Her of spectral classes A-F has been proceed, obtained with a 1.5-meter telescope PTT-150 (Russian Turkish Telescope-150). As a result of processing the spectra, the equivalent widths of unbend and weakly blended absorption lines were measured, 350 lines this star. The measured equivalent line widths can be used for other studies of the atmospheres of the A-F stars composition. Stars with temperatures of 8000-9000 K show a significant excess of elements heavier than iron and some deficiency of light elements. These results, apparently, are a consequence of the effects of light pressure and gravitational diffusion of atoms and ions in atmospheres of calm and radiative atmospheres of A-stars.

Protoplanetary Disk Rings as Sites for Planetesimal Formation

Abstract Axisymmetric dust rings are a ubiquitous feature of young protoplanetary disks. These rings are likely caused by pressure bumps in the gas profile; a small bump can induce a traffic-jam-like pattern in the dust density, while a large bump may halt radial dust drift entirely. The resulting increase in dust concentration may trigger planetesimal formation by the streaming instability (SI), as the SI itself requires some initial concentration of dust. Here we present the first 3D simulations of planetesimal formation in the presence of a pressure bump modeled specifically after those seen by Atacama Large Millimeter/submillimeter Array. We place a pressure bump at the center of a large 3D shearing box, along with an initial solid-to-gas ratio of Z = 0.01, and we include both particle back-reaction and particle self-gravity. We consider millimeter-sized and centimeter-sized particles separately. For simulations with centimeter-sized particles, we find that even a small pressure bump leads to the formation of planetesimals via the SI; a pressure bump does not need to fully halt radial particle drift for the SI to become efficient. Furthermore, pure gravitational collapse via concentration in pressure bumps (such as would occur at sufficiently high concentrations and without the SI) is not responsible for planetesimal formation. For millimeter-sized particles, we find tentative evidence that planetesimal formation does not occur. If this result is confirmed at higher resolution, it could put strong constraints on where planetesimals can form. Ultimately, our results show that for centimeter-sized particles planetesimal formation in pressure bumps is extremely robust.

Relationships between the Stellar, Gaseous, and Star Formation Disks in LITTLE THINGS Dwarf Irregular Galaxies: Indirect Evidence for Substantial Fractions of Dark Molecular Gas

Abstract The stellar, gaseous and young stellar disks in the LITTLE THINGS sample of nearby dwarf irregular galaxies are fitted with functions to search for correlations between the parameters. We find that the H i radial profiles are generally flatter in the center and fall faster in the outer regions than the V-band profiles, while young stars are more centrally concentrated, especially if the H i is more centrally flat. This pattern suggests that the H i is turning into molecules in the center, and the molecular clouds are forming stars and FUV. A model that assumes the molecular surface density is proportional to the total gas surface density to a power of 1.5 or 2, in analogy with the Kennicutt–Schmidt relation, reproduces the relationship between the ratio of the visible to the H i scale length and the H i Sérsic index. The molecular fraction is estimated as a function of radius for each galaxy by converting the FUV to a molecular surface density using conventional calibrations. The average molecular fraction inside 3R D is 23% ± 17%. However, the break in the stellar surface brightness profile has no unified tracer related to star formation.

Chemo-kinematics of the Gaia RR Lyrae: the halo and the disc

ABSTRACT We present the results of a multicomponent kinematic model of a large sample of RR Lyrae detected by Gaia. By imposing a fourfold symmetry and employing Gaia proper motions, we are able to infer the behaviour of the velocity ellipsoid between ≈3 and ≈30 kpc from the centre of the Galaxy. We detect the presence of two distinct components: a dominant non-rotating halo-like population and a much smaller rotating disc-like population. We demonstrate that the halo RR Lyrae can be described as a superposition of an isotropic and radially biased parts. The radially biased portion of the halo is characterized by a high orbital anisotropy β ≈ 0.9 and contributes between 50 per cent and 80 per cent of the halo RR Lyrae at 5 < R(kpc)<25. In line with previous studies, we interpret this high-β component as the debris cloud of the ancient massive merger also known as the Gaia Sausage (GS) whose orbital extrema we constrain. The light-curve properties of the RR Lyrae support the kinematic decomposition: the GS stars are more metal-rich and boast higher fractions of Oosterhoff Type 1 and high-amplitude short period (HASP) variables compared to the isotropic halo component. The metallicity/HASP maps reveal that the inner 10 kpc of the halo is likely inhabited by the RR Lyrae born in situ. The mean azimuthal speed and the velocity dispersion of the disc RR Lyrae out to R ≈ 30 kpc are consistent with the behaviour of a young and metal-rich thin disc stellar population.

The Influence of the Secular Perturbation of an Intermediate-mass Companion. I. Eccentricity Excitation of Disk Stars at the Galactic Center

Abstract There is a dense group of OB and Wolf–Rayet stars within a fraction of a parsec from the supermassive black hole (SMBH) at the Galactic Center. These stars appear to be coeval and relatively massive. A subgroup of these stars orbits on the same plane. If they emerged with low- to modest-eccentricity orbits from a common gaseous disk around the central SMBH, their inferred life span would not be sufficiently long to account for the excitation of their high orbital eccentricity through dynamical relaxation. Here we analyze the secular perturbation of Galactic Center stars by an intermediate-mass companion (IMC) as a potential mechanism to account for these young disk stars’ high eccentricity. This IMC may be either an intermediate-mass black hole or a compact cluster such as IRS 13E. If its orbital angular momentum vector is antiparallel to that of the disk stars, this perturbation would be effective in exciting the eccentricity of stars with orbital precession rates that resonate with the IMC’s precession rate. If it orbits around the SMBH in the same direction as the disk stars, the eccentricity of the young stars can still be highly excited by the IMC during the depletion of their natal disk, possibly associated with the launch of the Fermi bubble. In this scenario, the IMC’s precession rate decreases, and its secular resonance sweeps through the proximity of the young stars. We carry out numerical simulations with various inclination angles between the orbits of the IMC and the disk stars and show that this secular interaction is a robust mechanism to excite the eccentricity and inclination of some disk stars.

A microstructure-based modeling approach to assess aging-sensitive mechanics of human intervertebral disc

Background and objectiveThe human body soft tissues are hierarchic structures interacting in a complex manner with the surrounding biochemical environment. The loss of soft tissues functionality with age leads to more vulnerability regarding to the external mechanical loadings and increases the risk of injuries. As a main example of the human body soft tissues, the intervertebral disc mechanical response evolution with age is explored. Although the age-dependence of the intervertebral disc microstructure is a well-known feature, no noticeable age effect on the disc stiffness is evidenced in the in-vitro experimental studies of the literature. So, if the disc intrinsic mechanics remains constant, how to explain the correlation of disc degeneration and disc functionality loss with age. MethodsA microstructure-based modeling approach was developed to assess in-silico the aging-sensitive mechanics of human intervertebral disc. The model considers the relationship between stress/volumetric macro-response and microstructure along with effective age effects acting at the lamellar and multi-lamellar scales. The stress-stretch and transversal responses of the different disc regions were computed for various age groups (13-18, 36, 58, 69 and 82 years old) and their evolution with age was studied. ResultsWhile matching with in-vitro experimental data, the predicted stiffness was found to increase while passing from adolescent young discs to mature older discs and then to remain almost constant for the rest of life. Important age-related changes in the disc transversal behavior were also predicted affecting the flexibility of the disc, changing its volumetric behavior, and modifying its dimensions. ConclusionThe developed approach was found able to bring new conclusions about age-dependent mechanical properties including regional dependency. The disc mechanics in terms of rigidity, radial and axial transversal responses were found to alter going from adolescent to middle age where the disc reaches a certain maturity. After reaching maturity, the mechanical properties undergo very slight changes until becoming almost constant with age.

Spectroscopy and Kinematics of the High-Latitude UX Ori Type Star V1117 Her

Results from a study of low resolution spectra and kinematics of the star V1117 Her located at a high galactic latitude b = +33°.8 are presented. It is shown that this star has A7 IV photospheric class, luminosity L ≈ 26 Lʘ, and spectral signs of accretion activity. This confirms its previous classification as a young Ae Herbig star with photometric UX Ori type variability. In addition, the parallax of V1117 Her in the GAIA DR2 catalog corresponds to a distance of D ≈ 1.4 kpc to it, which represents a height Z ≈ 800 pc of the star above the galactic plane. Here the kinetics of the star indicates its more probable formation in situ, outside the plane of the young disk. A possible scenario for the formation of V1117 Her is discussed briefly.

Investigating the magnetospheric accretion process in the young pre-transitional disk system DoAr 44 (V2062 Oph)

Context. Young stars interact with their accretion disk through their strong magnetosphere. Aims. We aim to investigate the magnetospheric accretion/ejection process in the young stellar system DoAr 44 (V2062 Oph). Methods. We monitored the system over several rotational cycles, combining high-resolution spectropolarimetry at both optical and near-IR wavelengths with long-baseline near-IR inteferometry and multicolor photometry. Results. We derive a rotational period of 2.96 d from the system’s light curve, which is dominated by stellar spots. We fully characterize the central star’s properties from the high signal-to-noise, high-resolution optical spectra we obtained during the campaign. DoAr 44 is a young 1.2 M⊙ star, moderately accreting from its disk (Ṁacc = 6.5 10−9 M⊙ yr−1), and seen at a low inclination (i ≃ 30°). Several optical and near-IR line profiles probing the accretion funnel flows (Hα, Hβ, HeI 1083 nm, Paβ) and the accretion shock (HeI 587.6 nm) are modulated at the stellar rotation period. The most variable line profile is HeI 1083 nm, which exhibits modulated redshifted wings that are a signature of accretion funnel flows, as well as deep blueshifted absorptions indicative of transient outflows. The Zeeman-Doppler analysis suggests the star hosts a mainly dipolar magnetic field, inclined by about 20° onto the spin axis, with an intensity reaching about 800 G at the photosphere, and up to 2 ± 0.8 kG close to the accretion shock. The magnetic field appears strong enough to disrupt the inner disk close to the corotation radius, at a distance of about 4.6 R⋆ (0.043 au), which is consistent with the 5 R⋆ (0.047 au) upper limit we derived for the size of the magnetosphere in our Paper I from long baseline interferometry. Conclusions. DoAr 44 is a pre-transitional disk system, exhibiting a 25–30 au gap in its circumstellar disk, with the inner and outer disks being misaligned. On a scale of 0.1 au or less, our results indicate that the system is steadily accreting from its inner disk through its tilted dipolar magnetosphere. We conclude that in spite of a highly structured disk on the large scale, perhaps the signature of ongoing planetary formation, the magnetospheric accretion process proceeds unimpeded at the star-disk interaction level.

Bar resonances and low angular momentum moving groups in the Galaxy revealed by their stellar ages

We use the second Gaia data release to dissect the Milky Way disc in phase-space and relative ages. We confirm and report the existence of multiple velocity moving groups at low azimuthal velocities and angular momenta, below Arcturus, regularly separated by ∼18−20 km s−1 in azimuthal velocity. Such features were predicted to exist more than ten years ago, based on the reaction of the Milky Way to a perturbation in the disc undergoing phase-mixing. These structures appear slightly younger than their phase-space surroundings and reach up to high (solar) metallicities, which argues against an extra-galactic origin. We also identify, in terms of relative age, many of the classical ridges in the plane of azimuthal velocity versus Galactocentric radius, which are traditionally associated with resonance features. These ridges are also younger than their phase-space surroundings in accordance with predictions from recent state-of-the-art cosmological hydrodynamical simulations of Milky Way-like galaxies. We study the response of dynamically young and old stellar disc populations to resonances from an analytic model of a large bar which, remarkably, reproduces qualitatively the trends seen in the data for the classical ridges close to circularity. Our results reinforce the idea that the Galactic disc is being shaped by both internal and external perturbations, along with the fact that while absolute isochrone ages have to be taken with great care, exploring the dynamical structure of the disc in stellar ages, especially with future asteroseismic data, will provide much stronger constraints than metallicity and abundance trends alone.

Four annular structures in a protostellar disk less than 500,000 years old.

Annular structures (rings and gaps) in disks around pre-main-sequence stars have been detected in abundance towards classII protostellar objects that are approximately 1,000,000years old1. These structures are often interpreted as evidence of planet formation1-3, with planetary-mass bodies carving rings and gaps in the disk4. This implies that planet formation may already be underway in even younger disks in the classI phase, when the protostar is still embedded in a larger-scale dense envelope of gas and dust5. Only within the past decade have detailed properties of disks in the earliest star-forming phases been observed6,7. Here we report 1.3-millimetre dust emission observations with a resolution of five astronomical units that show four annular substructures in the disk of the young (less than500,000 years old)8 protostar IRS63. IRS63 is a single classI source located in the nearby Ophiuchus molecular cloud at a distance of 144 parsecs9, and is one of the brightest classI protostars at millimetre wavelengths. IRS63 also has a relatively large disk compared to other young disks (greater than 50astronomical units)10. Multiple annular substructures observed towards disks at young ages can act as an early foothold for dust-grain growth, which is a prerequisite of planet formation. Whether or not planets already exist in the disk of IRS63, it is clear that the planet-formation process begins in the initial protostellar phases, earlier than predicted by current planet-formation theories11.

Temperature Structures of Embedded Disks: Young Disks in Taurus Are Warm

Abstract The chemical composition of gas and ice in disks around young stars sets the bulk composition of planets. In contrast to protoplanetary disks (Class II), young disks that are still embedded in their natal envelope (Class 0 and I) are predicted to be too warm for CO to freeze out, as has been confirmed observationally for L1527 IRS. To establish whether young disks are generally warmer than their more evolved counterparts, we observed five young (Class 0/I and I) disks in Taurus with the Atacama Large Millimeter/submillimeter Array, targeting C17O 2 − 1, H2CO , HDO , and CH3OH 5 K − 4 K transitions at 0.″48 × 0.″31 resolution. The different freeze-out temperatures of these species allow us to derive a global temperature structure. C17O and H2CO are detected in all disks, with no signs of CO freeze-out in the inner ∼100 au and a CO abundance close to ∼10−4. The H2CO emission originates in the surface layers of the two edge-on disks, as witnessed by the especially beautiful V-shaped emission pattern in IRAS 04302+2247. HDO and CH3OH are not detected, with column density upper limits more than 100 times lower than for hot cores. Young disks are thus found to be warmer than more evolved protoplanetary disks around solar analogs, with no CO freeze-out (or only in the outermost part of ≳100 au disks) or processing. However, they are not as warm as hot cores or disks around outbursting sources and therefore do not have a large gas-phase reservoir of complex molecules.

The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. III. Substructures in Protostellar Disks

Abstract The prevalence of substructures in ∼1–10 Myr old protoplanetary disks, which are often linked to planet formation, has raised the question of how early such features form and, as a corollary, how early planet formation begins. Here we present observations of seven protostellar disks (aged ∼ 0.1–1 Myr) from the Very Large Array/Atacama Large Millimeter/Submillimeter Array Nascent Disk and Multiplicity Survey of Orion Protostars (VANDAM: Orion) that show clear substructures, thereby demonstrating that these features can form early in the lifetimes of disks. We use simple analytic models as well as detailed radiative transfer modeling to characterize their structure. In particular we show that at least four of the sources have relatively massive envelopes, indicating that they are particularly young, likely the youngest disks with substructures known to date. Several of these disks also have emission from an inner disk that is offset from the center of the ring structure. Given the size of the cleared-out regions of the disk, it is unclear, however, whether these features are related to planet formation, or rather if they are signposts of close-separation binary formation at early times.

Discovery of a Nearby Young Brown Dwarf Disk

Abstract We report the discovery of the youngest brown dwarf with a disk at 102 pc from the Sun, WISEA J120037.79−784508.3 (W1200−7845), via the Disk Detective citizen science project. We establish that W1200−7845 is located in the Myr old ε Cha association. Its spectral energy distribution (SED) exhibits clear evidence of an infrared (IR) excess, indicative of the presence of a warm circumstellar disk. Modeling this warm disk, we find the data are best fit using a power-law description with a slope α = −0.94, which suggests that it is a young, Class II type disk. Using a single blackbody disk fit, we find and . The near-IR spectrum of W1200−7845 matches a spectral type of M6.0 0.5, which corresponds to a low surface gravity object, and lacks distinctive signatures of strong Paβ or Brγ accretion. Both our SED fitting and spectral analysis indicate that the source is cool (T eff = 2784–2850 K), with a mass of 42–58 M Jup, well within the brown dwarf regime. The proximity of this young brown dwarf disk makes the system an ideal benchmark for investigating the formation and early evolution of brown dwarfs.

Dynamical signatures of Rossby vortices in cavity-hosting disks

Context. Planets are formed amidst young circumstellar disks of gas and dust. The latter is traced by thermal radiation, where strong asymmetric clumps have been observed in a handful of cases. These dust traps could be key to understanding the early stages of planet formation, when solids grow from micron-size to planetesimals. Aims. Vortices are among the few known asymmetric dust trapping scenarios. The present work aims to predict their characteristics in a complementary observable. Namely, line-of-sight velocities are well suited to trace the presence of a vortex. Moreover, the dynamics of disks is subject to recent developments. Methods. Two-dimensional hydro simulations were performed in which a vortex forms at the edge of a gas-depleted region. We derived idealized line-of-sight velocity maps, varying disk temperature and orientation relative to the observer. The signal of interest, as a small perturbation to the dominant axisymmetric component in velocity, may be isolated in observational data using a proxy for the dominant quasi-Keplerian velocity. We propose that the velocity curve on the observational major axis be such a proxy. Results. Applying our method to the disk around HD 142527 as a study case, we predict that line-of-sight velocities are barely detectable by currently available facilities, depending on disk temperature. We show that corresponding spirals patterns can also be detected with similar spectral resolutions, which will help to test against alternative explanations.

ALMA Observations of Young Eruptive Stars: Continuum Disk Sizes and Molecular Outflows

Abstract We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of four young, eruptive star–disk systems at 0.″4 resolution: two FUors (V582 Aur and V900 Mon), one EXor (UZ Tau E), and one source with an ambiguous FU/EXor classification (GM Cha). The disks around GM Cha, V900 Mon, and UZ Tau E are resolved. These observations increase the sample of FU/EXors observed at subarcsecond resolution by 15%. The disk sizes and masses of FU/EXors objects observed by ALMA so far suggest that FUor disks are more massive than Class 0/I disks in Orion and Class II disks in Lupus of similar size. EXor disks in contrast do not seem to be distinguishable from these two populations. We reach similar conclusions when comparing the FU/EXor sample to the Class I and Class II disks in Ophiuchus. FUor disks around binaries are host to more compact disks than those in single-star systems, similar to noneruptive young disks. We detect a wide-angle outflow around GM Cha in 12CO emission, wider than typical Class I objects and more similar to those found around some FUor objects. We use radiative transfer models to fit the continuum and line data of the well-studied disk around UZ Tau E. The line data are well described by a Keplerian disk, with no evidence of outflow activity (similar to other EXors). The detection of wide-angle outflows in FUors but not in EXors support the current picture in which FUors are more likely to represent an accretion burst in the protostellar phase (Class I), while EXors are smaller accretion events in the protoplanetary (Class II) phase.

Dust masses of young disks: constraining the initial solid reservoir for planet formation

Context. Recent years have seen building evidence that planet formation starts early, in the first ~0.5 Myr. Studying the dust masses available in young disks enables us to understand the origin of planetary systems given that mature disks are lacking the solid material necessary to reproduce the observed exoplanetary systems, especially the massive ones. Aims. We aim to determine if disks in the embedded stage of star formation contain enough dust to explain the solid content of the most massive exoplanets. Methods. We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (1.1–1.3 mm) continuum observations of embedded disks in the Perseus star-forming region together with Very Large Array (VLA) Ka-band (9 mm) data to provide a robust estimate of dust disk masses from the flux densities measured in the image plane. Results. We find a strong linear correlation between the ALMA and VLA fluxes, demonstrating that emission at both wavelengths is dominated by dust emission. For a subsample of optically thin sources, we find a median spectral index of 2.5 from which we derive the dust opacity index β = 0.5, suggesting significant dust growth. Comparison with ALMA surveys of Orion shows that the Class I dust disk mass distribution between the two regions is similar, but that the Class 0 disks are more massive in Perseus than those in Orion. Using the DIANA opacity model including large grains, with a dust opacity value of κ9 mm = 0.28 cm2 g−1, the median dust masses of the embedded disks in Perseus are 158 M⊕ for Class 0 and 52 M⊕ for Class I from the VLA fluxes. The lower limits on the median masses from ALMA fluxes are 47 M⊕ and 12 M⊕ for Class 0 and Class I, respectively, obtained using the maximum dust opacity value κ1.3 mm = 2.3 cm2 g−1. The dust masses of young Class 0 and I disks are larger by at least a factor of ten and three, respectively, compared with dust masses inferred for Class II disks in Lupus and other regions. Conclusions. The dust masses of Class 0 and I disks in Perseus derived from the VLA data are high enough to produce the observed exoplanet systems with efficiencies acceptable by planet formation models: the solid content in observed giant exoplanets can be explained if planet formation starts in Class 0 phase with an efficiency of ~15%. A higher efficiency of ~30% is necessary if the planet formation is set to start in Class I disks.

The age–chemical abundance structure of the Galactic disc – II. α-dichotomy and thick disc formation

ABSTRACT We extend our previous work on the age–chemical abundance structure of the Galactic outer disc to the inner disc (4 < r < 8 kpc) based on the SDSS/APOGEE survey. Different from the outer disc, the inner disc stars exhibit a clear bimodal distribution in the [Mg/Fe]–[Fe/H] plane. While a number of scenarios have been proposed in the literature, it remains challenging to recover this bimodal distribution with theoretical models. To this end, we present a chemical evolution model embedding a complex multiphase inner disc formation scenario that matches the observed bimodal [Mg/Fe]–[Fe/H] distribution. In this scenario, the formation of the inner disc is dominated by two main starburst episodes $6\,$Gyr apart with secular, low-level star formation activity in between. In our model, the first starburst occurs at early cosmic times ($t\sim 1\,$ Gyr) and the second one $6\,$ Gyr later at a cosmic time of $t\sim 7\,$ Gyr. Both these starburst episodes are associated with gas accretion events in our model, and are quenched rapidly. The first starburst leads to the formation of the high-α sequence, and the second starburst leads to the formation of the metal-poor low-α sequence. The metal-rich low-α stars, instead, form during the secular evolution phase between the two bursts. Our model shows that the α-dichotomy originates from the rapid suppression of star formation after the first starburst. The two starburst episodes are likely to be responsible for the formation of the geometric thick disc (z >1 kpc), with the old inner thick disc and the young outer thick disc forming during the first and the second starbursts, respectively.

Validating scattering-induced (sub)millimetre disc polarization through the spectral index, wavelength-dependent polarization pattern, and polarization spectrum: the case of HD 163296

ABSTRACT A number of young circumstellar discs show strikingly ordered (sub)millimetre polarization orientations along the minor axis, which is strong evidence for polarization due to scattering by ∼0.1 mm-sized grains. To test this mechanism further, we model the ALMA dust continuum and polarization data of HD 163296 using radmc-3d. We find that scattering by grains with a maximum size of 90 μm simultaneously reproduces the polarization observed at Band 7 and the unusually low spectral index (α ∼ 1.5) between Bands 7 and 6 in the optically thick inner disc as a result of more efficient scattering at the shorter wavelength. The low spectral index of ∼2.5 inferred for the optically thin gaps is reproduced by the same grains, as a result of telescope beam averaging of the gaps (with an intrinsic α ∼ 4) and their adjacent optically thick rings (where α ≲ 2). The tension between the grain sizes inferred from polarization and spectral index disappears because the low α values do not require large mm-sized grains. In addition, the polarization fraction has a unique azimuthal variation: higher along the major axis than the minor axis in the gaps, but vice versa in the rings. We find a rapidly declining polarization spectrum (with p ∝ λ−3 approximately) in the gaps, which becomes flattened or even inverted towards short wavelengths in the optically thick rings. These contrasting behaviours in the rings and gaps provide further tests for scattering-induced polarization via resolved multiwavelength observations.