We present the first high-resolution sub-mm survey of both dust and gas for a large population of protoplanetary disks. Characterizing fundamental properties of protoplanetary disks on a statistical level is critical to understanding how disks evolve into the diverse exoplanet population. We use ALMA to survey 89 protoplanetary disks around stars with M * > 0.1 M in the young (1-3 Myr), nearby (150-200 pc) Lupus complex. Our observations cover the 890 µm continuum and the 13 CO and C 18 O 3-2 lines. We use the sub-mm continuum to constrain M dust to a few Martian masses (0.2-0.4 M ⊕ ) and the CO isotopologue lines to constrain M gas to roughly a Jupiter mass (assuming ISM-like [CO]/[H 2 ] abundance). Of 89 sources, we detect 62 in continuum, 36 in 13 CO, and 11 in C 18 O at > 3σ significance. Stacking individually undetected sources limits their average dust mass to 6 Lunar masses (0.03 M ⊕ ), indicating rapid evolution once disk clearing begins. We find a positive correlation between M dust and M * , and present the first evidence for a positive correlation between M gas and M * , which may explain the dependence of giant planet frequency on host star mass. The mean dust mass in Lupus is 3× higher than in Upper Sco, while the dust mass distributions in Lupus and Taurus are statistically indistinguishable. Most detected disks have M gas 1 M Jup and gas-to-dust ratios < 100, assuming ISM-like [CO]/[H 2 ] abundance; unless CO is very depleted, the inferred gas depletion indicates that planet formation is well underway by a few Myr and may explain the unexpected prevalence of super-Earths in the exoplanet population.

A model for irradiated dust disks around Herbig Ae stars is proposed. The model is based on the flaring disk model of Chiang & Goldreich (1997, henceforth CG97), but with the central regions of the disk removed. The inner rim of the disk is puffed up and is much hotter than the rest of the disk, because it is directly exposed to the stellar flux. If located at the dust evaporation radius, its reemitted flux produces a conspicuous bump in the SED which peaks at 2-3 micron. We propose that this emission is the explanation for the near-infrared bump observed in the SEDs of Herbig Ae stars. We study for which stellar parameters this bump would be observable, and find that it is the case for Herbig Ae stellar parameters but not for T-Tauri stars, confirming what is found from the observations. We also study the effects of the shadow cast by the inner rim over the rest of the flaring disk. The shadowed region can be quite large, and under some circumstances the entire disk may lie in the shadow. This shadowed region will be much cooler than an unshadowed flaring disk, since its only heating sources are radial radiative diffusion and possible indirect sources of irradiation. Under certain special circumstances the shadowing effect can suppress, or even completely eliminate, the 10 micron emission feature from the spectrum, which might explain the anomalous SEDs of some isolated Herbig Ae stars in the sample of Meeus et al. (2001). At much larger radii the disk emerges from the shadow, and continues as a flaring disk towards the outer edge. The emission from the inner rim contributes significantly to the irradiation of this flaring disk. The complete semi-analytical model, including structure of the inner edge, shadowed region and the flared outer part, is described in detail in this paper, and we show examples of the general behavior of the model for varying parameters.

Abstract. This paper presents a study of the accretion properties of 19 very low mass objects (M ∼ 0.01−0.1 M ) in the regions Chamaeleon I and ρ Oph. For 8 objects we obtained high resolution Hα profiles and determined mass accretion rateṀ ac and accretion luminosity L ac . Paβ is detected in emission in 7 of the 10 ρ Oph objects, but only in one in Cha I. Using objects for which we have both a determination of L ac from Hα and a Paβ detection, we show that the correlation between the Paβ luminosity and luminosity L ac , found by Muzerolle et al. (1998) for T Tauri stars in Taurus, extends to objects with mass ∼0.03 M ; L(Paβ) can be used to measure L ac also in the substellar regime. The results were less conclusive for Brγ, which was detected only in 2 objects, neither of which had an Hα estimate ofṀ ac . Using the relation between L(Paβ) and L ac we determined the accretion rate for all the objects in our sample (including those with no Hα spectrum), more than doubling the number of substellar objects with knownṀ ac . When plotted as a function of the mass of the central object together with data from the literature, our results confirm the trend of lowerṀ ac for lower M , although with a large spread. Some of the spread is probably due to an age effect; our very young objects in ρ Oph have on average an accretion rate at least one order of magnitude higher than objects of similar mass in older regions. As a side product, we found that the width of Hα measured at 10% peak intensity is not only a qualitative indicator of the accreting nature of very low mass objects, but can be used to obtain a quantitative, although not very accurate, estimate ofṀ ac over a large mass range, from T Tauri stars to brown dwarfs. Finally, we found that some of our objects show evidence of mass-loss in their optical spectra.

The mass accretion rate,Ṁ acc , is a key quantity for the understanding of the physical processes governing the evolution of accretion discs around young low-mass (M 2.0M ) stars and substellar objects (YSOs). We present here the results of a study of the stellar and accretion properties of the (almost) complete sample of class II and transitional YSOs in the Lupus I, II, III and IV clouds, based on spectroscopic data acquired with the VLT/X-Shooter spectrograph. Our study combines the dataset from our previous work with new observations of 55 additional objects. We have investigated 92 YSO candidates in total, 11 of which have been definitely identified with giant stars unrelated to Lupus. The stellar and accretion properties of the 81 bona fide YSOs, which represent more than 90% of the whole class II and transition disc YSO population in the aforementioned Lupus clouds, have been homogeneously and self-consistently derived, allowing for an unbiased study of accretion and its relationship with stellar parameters. The accretion luminosity, L acc , increases with the stellar luminosity, L , with an overall slope of ∼1.6, similar but with a smaller scatter than in previous studies. There is a significant lack of strong accretors below L ≈0.1L , where L acc is always lower than 0.01 L . We argue that the L acc -L slope is not due to observational biases, but is a true property of the Lupus YSOs. The logṀ acclogM correlation shows a statistically significant evidence of a break, with a steeper relation for M 0.2 M and a flatter slope for higher masses. The bimodality of theṀ acc -M relation is confirmed with four different evolutionary models used to derive the stellar mass. The bimodal behaviour of the observed relationship supports the importance of modelling self-gravity in the early evolution of the more massive discs, but other processes, such as photo-evaporation and planet formation during the YSO's lifetime, may also lead to disc dispersal on different timescales depending on the stellar mass. The sample studied here more than doubles the number of YSOs with homogeneously and simultaneously determined L acc and luminosity, L line , of many permitted emission lines. Hence, we also refined the empirical relationships between L acc and L line on a more solid statistical basis.

We present VLT/X-shooter observations of a sample of 36 accreting low-mass stellar and substellar objects (YSOs) in the Lupus star-forming region, spanning a range in mass from ∼0.03 to ∼1.2 M , but mostly with 0.1 M < M < 0.5 M . Our aim is twofold: firstly, to analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (L acc ), and in turn the accretion rate (Ṁ acc ), was derived by modelling the excess emission from the UV to the near-infrared as the continuum emission of a slab of hydrogen. We computed the flux and luminosity (L line ) of many emission lines of H , He , and Ca ii, observed simultaneously in the range from ∼330 nm to 2500 nm. The luminosity of all the lines is well correlated with L acc . We provide empirical relationships between L acc and the luminosity of 39 emission lines, which have a lower dispersion than relationships previously reported in the literature. Our measurements extend the Paβ and Brγ relationships to L acc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies of measuring L acc andṀ acc yield significantly different results: Hα line profile modelling may underestimateṀ acc by 0.6 to 0.8 dex with respect toṀ acc derived from continuum-excess measures. These differences may explain the probably spurious bi-modal relationships betweenṀ acc and other YSOs properties reported in the literature. We derivedṀ acc in the range 2 × 10 −12 -4 × 10 −8 M yr −1 and conclude thatṀ acc ∝ M 1.8(±0.2) , with a dispersion lower by a factor of about 2 than in previous studies. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude inṀ acc , confirming previous suggestions that the geometry of the accretion flow controls the rate at which the disc material accretes onto the central star.

We present Atacama Large Millimeter and Submillimeter Array observations of the protoplanetary disk around the Herbig Ae star HD 163296 that trace the spatial distribution of millimeter-sized particles and cold molecular gas on spatial scales as small as 25 astronomical units (A.U.). The image of the disk recorded in the 1.3 mm continuum emission reveals three dark concentric rings that indicate the presence of dust depleted gaps at about 60, 100, and 160 A.U. from the central star. The maps of the 12 CO, 13 CO, and C 18 O J ¼ 2 − 1 emission do not show such structures but reveal a change in the slope of the radial intensity profile across the positions of the dark rings in the continuum image. By comparing the observations with theoretical models for the disk emission, we find that the density of CO molecules is reduced inside the middle and outer dust gaps. However, in the inner ring there is no evidence of CO depletion. From the measurements of the dust and gas densities, we deduce that the gas-to-dust ratio varies across the disk and, in particular, it increases by at least a factor 5 within the inner dust gap compared to adjacent regions of the disk. The depletion of both dust and gas suggests that the middle and outer rings could be due to the gravitational torque exerted by two Saturn-mass planets orbiting at 100 and 160 A.U. from the star. On the other hand, the inner dust gap could result from dust accumulation at the edge of a magnetorotational instability dead zone, or from dust opacity variations at the edge of the CO frost line. Observations of the dust emission at higher angular resolution and of molecules that probe dense gas are required to establish more precisely the origins of the dark rings observed in the HD 163296 disk.

Aims. The aim of this paper is to provide a measurement of the mass accretion rate in a large, complete sample of objects in the core of the star forming region ρ Oph. Methods. The sample includes most of the objects (104 out of 111) with evidence of a circumstellar disk from mid-infrared photometry; it covers a stellar mass range from about 0.03 to 3 M and it is complete to a limiting mass of ∼0.05 M . We used J and K-band spectra to derive the mass accretion rate of each object from the intensity of the hydrogen recombination lines, Paβ or Brγ. For comparison, we also obtained similar spectra of 35 diskless objects. Results. The results show that emission in these lines is only seen in stars with disks, and can be used as an indicator of accretion. However, the converse does not hold, as about 50% of our disk objects do not have detectable line emission. The measured accretion rates show a strong correlation with the mass of the central object (Ṁ acc ∝ M 1.8±0.2 ) and a large spread, of two orders of magnitude at least, for any interval of M . A comparison with existing data for Taurus shows that the objects in the two regions have similar behaviour, at least for objects more massive than ∼0.1 M . The implications of these results are briefly discussed.

Aims. We attempt to explain grain growth to mm sized particles and their retention in the outer regions of protoplanetary disks, as observed at sub-mm and mm wavelengths, by investigating whether strong inhomogeneities in the gas density profiles can decelerate excessive radial drift and help the dust particles to grow. Methods. We use coagulation/fragmentation and disk-structure models, to simulate the evolution of dust in a bumpy surface density profile, which we mimic with a sinusoidal disturbance. For different values of the amplitude and length scale of the bumps, we investigate the ability of this model to produce and retain large particles on million-year timescales. In addition, we compare the pressure inhomogeneities considered in this work with the pressure profiles that come from magnetorotational instability. Using the Common Astronomy Software Applications ALMA simulator, we study whether there are observational signatures of these pressure inhomogeneities that can be seen with ALMA. Results. We present the conditions required to trap dust particles and the corresponding calculations predicting the spectral slope in the mm-wavelength range, to compare with current observations. Finally, we present simulated images using different antenna configurations of ALMA at different frequencies, to show that the ring structures will be detectable at the distances of either the Taurus Auriga or Ophiucus star-forming regions.