Protoplanetary disc ‘isochrones’ and the evolution of discs in the M – M d plane

Protoplanetary disc ‘isochrones’ and the evolution of discs in the M – M d plane 

Authors:

Lodato et al

Abstract:
In this paper, we compare simple viscous diffusion models for the disc evolution with the results of recent surveys of the properties of young protoplanetary discs. We introduce the useful concept of ‘disc isochrones’ in the accretion rate - disc mass plane and explore a set of Montecarlo realization of disc initial conditions. We find that such simple viscous models can provide a remarkable agreement with the available data in the Lupus star forming region, with the key requirement that the average viscous evolutionary timescale of the discs is comparable to the cluster age. Our models produce naturally a correlation between mass accretion rate and disc mass that is shallower than linear, contrary to previous results and in agreement with observations. We also predict that a linear correlation, with a tighter scatter, should be found for more evolved disc populations. Finally, we find that such viscous models can reproduce the observations in the Lupus region only in the assumption that the efficiency of angular momentum transport is a growing function of radius, thus putting interesting constraints on the nature of the microscopic processes that lead to disc accretion.

ALMA SURVEY OF LUPUS PROTOPLANETARY DISKS. I. DUST AND GAS MASSES

ALMA SURVEY OF LUPUS PROTOPLANETARY DISKS. I. DUST AND GAS MASSES

Authors:

Andsell et al

Abstract:

We present the first high-resolution sub-millimeter 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 the Atacama Large Millimeter/Submillimeter Array (ALMA) to survey 89 protoplanetary disks around stars with ${M}_{* }\gt 0.1\,{M}_{\odot }$ in the young (1–3 Myr), nearby (150–200 pc) Lupus complex. Our observations cover the 890 μm continuum and the 13CO and C18O 3–2 lines. We use the sub-millimeter continuum to constrain ${M}_{{\rm{dust}}}$ to a few Martian masses (0.2–0.4 M ⊕) and the CO isotopologue lines to constrain ${M}_{{\rm{gas}}}$ to roughly a Jupiter mass (assuming an interstellar medium (ISM)-like $[\mathrm{CO}]/[{{\rm{H}}}_{2}]$ abundance). Of 89 sources, we detect 62 in continuum, 36 in 13CO, and 11 in C18O at $\gt 3\sigma $ significance. Stacking individually undetected sources limits their average dust mass to $\lesssim 6$ Lunar masses (0.03 M ⊕), indicating rapid evolution once disk clearing begins. We find a positive correlation between ${M}_{{\rm{dust}}}$ and M *, and present the first evidence for a positive correlation between ${M}_{{\rm{gas}}}$ 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 ${M}_{{\rm{gas}}}\lesssim 1\,{M}_{{\rm{Jup}}}$ and gas-to-dust ratios $\lt 100$, assuming an ISM-like $[\mathrm{CO}]/[{{\rm{H}}}_{2}]$ 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.

ALMA Survey of Lupus Protoplanetary Disks I: Dust and Gas Masses

ALMA Survey of Lupus Protoplanetary Disks I: Dust and Gas Masses

Authors:

Andsell et al

Abstract:

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∗ greater than 0.1 M⊙ in the young (∼1-3 Myr), nearby (∼150-200 pc) Lupus complex. Our observations cover the 890 μm continuum and the 13CO and C18O 3-2 lines. We use the sub-mm continuum to constrain Mdust to a few Martian masses (0.2-0.4 M⊕) and the CO isotopologue lines to constrain Mgas to roughly a Jupiter mass (assuming ISM-like [CO]/[H2] abundance). Of 89 sources, we detect 62 in the continuum, 36 in 13CO, and 11 in C18O at greater than 3σ significance. Several new "transition disks" are found with relatively bright continuum and CO isotopologue emission. Stacking the 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 but non-linear correlation between Mdust and M∗, and also demonstrate for the first time a tentative positive correlation between Mgas and M∗. 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 from each other. Most detected disks have Mgas≲1 MJup and gas-to-dust ratios less than 100 when using our parameterized model framework; if confirmed, the inferred rapid gas depletion indicates that planet formation is largely complete by a few Myr, and may also explain the unexpected prevalence of super-Earths in the exoplanet population.

Circumstellar Disks Around Lupus Association T Tauri Stars are Unusually Short Lived

Evolution of the T Tauri star population in the Lupus association

Authors:

Galli et al

Abstract:

Aims:

In a recent study, we derived individual distances for 109 pre-main sequence stars that define the Lupus kinematic association of young stars. Here, we use these new distances to derive the masses and ages of Lupus T Tauri stars with the aim of better constraining the lifetime of their circumstellar disks.

Methods:

Using the photometric and spectroscopic information available in the literature, we computed the photospheric luminosity of 92 T Tauri stars in the Lupus association. Then, we estimated their masses and ages from theoretical evolutionary models. Based on Monte Carlo simulations and statistical tests, we compare the mass and age distribution of the classical T Tauri stars (CTTS) and weak-line T Tauri (WTTS) in our sample.

Results:

We show that the CTTSs are on average younger than the WTTSs and that the probability that both T~Tauri subclasses are drawn from the same mass and age parental distribution is very low. Our results favor the scenario proposed earlier for the Taurus-Auriga association, where the CTTSs evolve into WTTSs when their disks are fully accreted by the star. Based on an empirical disk model, we find that the average disk lifetime for the T Tauri stars in the Lupus association is τd=3×106(M∗/M⊙)0.55 yr.

Conclusions:

We find evidence that the average lifetime of the circumstellar disks in the Lupus association is shorter than in the Taurus-Auriga association and discuss the implications of this result.

34 Transitional Disks Candidates in Lupus

Identification of new transitional disk candidates in Lupus with Herschel

Authors:

Bustamante et al

Abstract:

New data from the Herschel Space Observatory are broadening our understanding of the physics and evolution of the outer regions of protoplanetary disks in star forming regions. In particular they prove to be useful to identify transitional disk candidates. The goals of this work are to complement the detections of disks and the identification of transitional disk candidates in the Lupus clouds with data from the Herschel Gould Belt Survey. We extracted photometry at 70, 100, 160, 250, 350 and 500 μm of all spectroscopically confirmed Class II members previously identified in the Lupus regions and analyzed their updated spectral energy distributions. We have detected 34 young disks in Lupus in at least one Herschel band, from an initial sample of 123 known members in the observed fields. Using the criteria defined in Ribas et al. (2013) we have identified five transitional disk candidates in the region. Three of them are new to the literature. Their PACS-70 μm fluxes are systematically higher than those of normal T Tauri stars in the same associations, as already found in T Cha and in the transitional disks in the Chamaeleon molecular cloud. Herschel efficiently complements mid-infrared surveys for identifying transitional disk candidates and confirms that these objects seem to have substantially different outer disks than the T Tauri stars in the same molecular clouds.