The disk mass is among the most important input parameter for every planet formation model to determine the number and masses of the planets that can form. We present an ALMA 887 μm survey of the disk population around objects from ∼2 to 0.03 M e in the nearby ∼2 Myr old ChamaeleonI star-forming region. We detect thermal dust emission from 66 out of 93 disks, spatially resolve 34 of them, and identify two disks with large dust cavities of about 45 au in radius. Assuming isothermal and optically thin emission, we convert the 887 μm flux densities into dust disk masses, hereafter M dust . We find that the -* M M dust relation is steeper than linear and of the form M dust ∝(M * )1.3-1.9 , where the range in the power-law index reflects two extremes of the possible relation between the average dust temperature and stellar luminosity. By reanalyzing all millimeter data available for nearby regions in a self-consistent way, we show that the 1-3 Myr old regions of Taurus, Lupus, and ChamaeleonI share the same -* M M dust relation, while the 10 Myr old UpperSco association has a steeper relation. Theoretical models of grain growth, drift, and fragmentation reproduce this trend and suggest that disks are in the fragmentation-limited regime. In this regime millimeter grains will be located closer in around lower-mass stars, a prediction that can be tested with deeper and higher spatial resolution ALMA observations.

We explore the effects of the expected higher cosmic ray (CR) ionization rates CR z on the abundances of carbon monoxide (CO), atomic carbon (C), and ionized carbon (C + ) in the H 2 clouds of star-forming galaxies. The study of Bisbas et al. is expanded by(a) using realistic inhomogeneous giant molecular cloud (GMC) structures, (b) a detailed chemical analysis behind the CR-induced destruction of CO, and (c) exploring the thermal state of CRirradiated molecular gas. CRs permeating the interstellar medium with 10 Galactic CR  z´( ) are found to significantly reduce the [CO]/[H 2 ] abundance ratios throughout the mass of a GMC. CO rotational line imaging will then show much clumpier structures than the actual ones. For 100 CR  z´(Galactic) this bias becomes severe, limiting the usefulnessof CO lines for recovering structural and dynamical characteristics of H 2 -rich galaxies throughout the universe, including many of the so-called main-sequence galaxies where the bulk of cosmic star formation occurs. Both C + and C abundances increase with rising CR

Since the discovery of the first directly-imaged, planetary-mass object, 2MASS 1207 b, several works have sought to explain a disparity between its observed temperature and luminosity. Given its known age, distance, and spectral type, 2MASS 1207 b is under-luminous by a factor of ∼10 (∼2.5 mags) when compared to standard models of brown-dwarf/giant-planet evolution. In this paper, we study three possible sources of 2MASS 1207 b's under-luminosity. First, we investigate Mohanty et al. (2007)'s hypothesis that a near edge-on disk, comprising large, gray-extincting grains, might be responsible for 2MASS 1207 b's under-luminosity. After radiative transfer modeling we conclude that the hypothesis is unlikely due to the lack of variability seen in multi-epoch photometry and unnecessary due to the increasing sample of under-luminous browndwarfs/giant-exoplanets that cannot be explained by an edge-on disk. Next, we test the analogous possibility that a spherical shell of dust, could explain 2MASS 1207 b's under-luminosity. Models containing enough dust to create ∼2.5 mags of extinction, placed at reasonable radii, are ruled out by our new Gemini/T-ReCS 8.7µm photometric upper-limit for 2MASS 1207 b. Finally, we investigate the possibility that 2MASS 1207 b is intrinsically cooler than the commonly used AMES-DUSTY fits to its spectrum, and thus it is not, in fact, under-luminous. New, thick cloud model grids by Madhusudhan et al. (2011) fit 2MASS 1207 b's 1-10µm SED well, but they do not quite fit its near-infrared spectrum. However, we suggest that with some "tuning", they might be capable of simultaneously reproducing 2MASS 1207 b's spectral shape and luminosity. In this case, the whole class of young, under-luminous brown-dwarfs/giant-exoplanets might be explained by atmospheres that are able to suspend thick, dusty clouds in their photospheres at lower temperatures than field brown-dwarfs.

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