Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion

We present high-resolution, high dynamic range column-density and color-temperature maps of the Orion complex using a combination of Planck dust-emission maps, Herschel dust-emission maps, and 2MASS NIR dust-extinction maps. The column-density maps combine the robustness of the 2MASS NIR extinction maps with the resolution and coverage of the Herschel and Planck dust-emission maps and constitute the highest dynamic range column-density maps ever constructed for the entire Orion complex, covering $0.01 , mathrm{mag} < A_K < 30 ,mathrm{mag}$, or $2 times 10^{20} , mathrm{cm}^{-2} < N < 5 times 10^{23} ,mathrm{cm}^{-2}$. We determined the ratio of the 2.2 microns extinction coefficient to the 850 microns opacity and found that the values obtained for both Orion A and B are significantly lower than the predictions of standard dust models, but agree with newer models that incorporate icy silicate-graphite conglomerates for the grain population. We show that the cloud projected pdf, over a large range of column densities, can be well fitted by a simple power law. Moreover, we considered the local Schmidt-law for star formation, and confirm earlier results, showing that the protostar surface density $Sigma_*$ follows a simple law $Sigma_* propto Sigma_{gas}^beta$, with $beta sim 2$.

Disk evolution in the solar neighborhood. I Disk frequencies from 1 to 100 Myr

We study the evolution of circumstellar disks in 22 young (1 to 100 Myr) nearby (within 500 pc) associations over the entire mass spectrum using photometry covering from the optical to the mid-infrared. We compiled a catalog of 2340 spectroscopically-confirmed members of these nearby associations. We analyzed their spectral energy distributions and searched for excess related to the presence of protoplanetary disks in a homogeneous way. Sensitivity limits and spatial completeness were also considered. We derive disk fractions as probed by mid-infrared excess in these regions. The unprecedented size of our sample allows us to confirm the timescale of disk decay reported in the literature and to find new trends. The fraction of excess sources increases systematically if measured at longer wavelengths. Disk percentages derived using different wavelength ranges should therefore be compared with caution. The dust probed at 22-24 um evolves slower than that probed at shorter wavelengths (3.4-12 um). Assuming an exponential decay, we derive a timescale tau=4.2-5.8 Myr at 22-24 um for primordial disks, compared to 2-3 Myr at shorter wavelength (3.4-12 um). Primordial disks disappear around 10 Myr, matching in time a brief increase of the number of evolved disks. The increase in timescale of excess decay at longer wavelength is compatible with inside-out disk clearing scenarios. The increased timescale of decay and larger dispersion in the distribution of disk fractions at 22-24 um suggest that the inner and outer zones evolve differently, the latter potentially following a variety of evolutionary paths. The drop of primordial disks and the coincident rise of evolved disks at 10 Myr are compatible with planet formation theories suggesting that the disappearance of the gas is immediately followed by the dynamical stirring of the disk.

Proper motions of cool and ultracool candidate members in the Upper Scorpius OB association

Proper motion measurements of the cool and ultracool populations in the Upper Scorpius OB association are crucial to confirm membership and to identify possible run-away objects. We cross-match samples of photometrically selected and spectroscopically confirmed cool and ultracool (K5<SpT<M8.5) candidate members in the Upper Scorpius OB association using the literature and the USNO-B and the UCAC2 catalogues. 251 of these objects have a USNO-B and/or UCAC2 counterpart with proper motion measurements. A significant fraction (19 objects, 7.6+-1.8%) of spectroscopically confirmed young objects show discrepant proper motion. They must either belong to unidentified coincident foreground associations, or originate from neighboring star forming regions or have recently experienced dynamical interactions within the association. The observed accretor and disc frequencies are lower among outliers, but with only 19 objects it is unreliable to draw firm statistical conclusions. Finally, we note that transverse velocities of very low mass members are indistinguishable from those of low mass members within 4km/s