Browsing by Subject "planetary systems :"

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Probing Dust Grain Evolution In IM Lupi's Circumstellar Disc - Multi-Wavelength Observations And Modelling Of The Dust Disc
(2008-10) Pinte, C.; Padgett, D. L.; Menard, F.; Stapelfeldt, K. R.; Schneider, G.; Olofsson, J.; Panic, O.; Augereau, J. C.; Duchene, G.; Krist, J.; Pontoppidan, K.; Perrin, M. D.; Grady, C. A.; Kessler-Silacci, J.; van Dishoeck, E. F.; Lommen, D.; Silverstone, M.; Hines, D. C.; Wolf, S.; Blake, G. A.; Henning, T.; Stecklum, B.; Kessler-Silacci, J.
Aims. We present a panchromatic study, involving a multiple technique approach, of the circumstellar disc surrounding the T Tauri star IM Lupi (Sz 82). Methods. We have undertaken a comprehensive observational study of IM Lupi using photometry, spectroscopy, millimetre interferometry and multi-wavelength imaging. For the first time, the disc is resolved from optical and near-infrared wavelengths in scattered light, to the millimetre regime in thermal emission. Our data-set, in conjunction with existing photometric data, provides an extensive coverage of the spectral energy distribution, including a detailed spectrum of the silicate emission bands. We have performed a simultaneous modelling of the various observations, using the radiative transfer code MCFOST, and analysed a grid of models over a large fraction of the parameter space via Bayesian inference. Results. We have constructed a model that can reproduce all of the observations of the disc. Our analysis illustrates the importance of combining a wide range of observations in order to fully constrain the disc model, with each observation providing a strong constraint only on some aspects of the disc structure and dust content. Quantitative evidence of dust evolution in the disc is obtained: grain growth up to millimetre-sized particles, vertical stratification of dust grains with micrometric grains close to the disc surface and larger grains which have settled towards the disc midplane, and possibly the formation of fluffy aggregates and/ or ice mantles around grains.
Probing Dust Grain Evolution In IM Lupi's Circumstellar Disc - Multi-Wavelength Observations And Modelling Of The Dust Disc
(2008-10) Pinte, C.; Padgett, D. L.; Menard, F.; Stapelfeldt, K. R.; Schneider, G.; Olofsson, J.; Panic, O.; Augereau, J. C.; Duchene, G.; Krist, J.; Pontoppidan, K.; Perrin, M. D.; Grady, C. A.; Kessler-Silacci, J.; van Dishoeck, E. F.; Lommen, D.; Silverstone, M.; Hines, D. C.; Wolf, S.; Blake, G. A.; Henning, T.; Stecklum, B.; Kessler-Silacci, J.
Aims. We present a panchromatic study, involving a multiple technique approach, of the circumstellar disc surrounding the T Tauri star IM Lupi (Sz 82). Methods. We have undertaken a comprehensive observational study of IM Lupi using photometry, spectroscopy, millimetre interferometry and multi-wavelength imaging. For the first time, the disc is resolved from optical and near-infrared wavelengths in scattered light, to the millimetre regime in thermal emission. Our data-set, in conjunction with existing photometric data, provides an extensive coverage of the spectral energy distribution, including a detailed spectrum of the silicate emission bands. We have performed a simultaneous modelling of the various observations, using the radiative transfer code MCFOST, and analysed a grid of models over a large fraction of the parameter space via Bayesian inference. Results. We have constructed a model that can reproduce all of the observations of the disc. Our analysis illustrates the importance of combining a wide range of observations in order to fully constrain the disc model, with each observation providing a strong constraint only on some aspects of the disc structure and dust content. Quantitative evidence of dust evolution in the disc is obtained: grain growth up to millimetre-sized particles, vertical stratification of dust grains with micrometric grains close to the disc surface and larger grains which have settled towards the disc midplane, and possibly the formation of fluffy aggregates and/ or ice mantles around grains.
The Spitzer c2d Survey Of Large, Nearby, Interstellar Clouds. X. The Chamaeleon II Pre-Main-Sequence Population As Observed With IRAC And MIPS
(2008-03) Alcala, Juan M.; Spezzi, Loredana; Chapman, Nicholas; Evans, Neal J.; Huard, Tracy L.; Jorgensen, Jes K.; Merin, Bruno; Stapelfeldt, Karl R.; Covino, E.; Frasca, Antonio; Gandolfi, Davide; Oliveira, Isa; Evans, Neal J.
We discuss the results from the combined IRAC and MIPS c2d Spitzer Legacy survey observations and complementary optical and NIR data of the Chamaeleon II (Cha II) dark cloud. We perform a census of the young population in an area of similar to 1.75 deg(2) and study the spatial distribution and properties of the cloud members and candidate pre-main-sequence (PMS) objects and their circumstellar matter. Our census is complete down to the substellar regime (M approximate to 0.03 M-circle dot). From the analysis of the volume density of the PMS objects and candidates we find two groups of objects with volume densities higher than 25 M-circle dot pc(-3) and 5-10 members each. A multiplicity fraction of about 13% +/- 3% is observed for objects with separations 0.8 '' < theta < 6.0 '' (142-1065 AU). No evidence for variability between the two epochs of the c2d IRAC data set, Delta t similar to 6 hr, is detected. We estimate a star formation efficiency of 1%-4%, consistent with the estimates for Taurus and Lupus, but lower than for Cha I. This might mean that different star formation activities in the Chamaeleon clouds reflect a different history of star formation. We also find that Cha II is turning some 6-7 M-circle dot into stars every Myr, which is low in comparison with the star formation rate in other c2d clouds. The disk fraction of 70%-80% that we estimate in Cha II is much higher than in other star-forming regions and indicates that the population in this cloud is dominated by objects with active accretion. Finally, the Cha II outflows are discussed; a new Herbig-Haro outflow, HH 939, driven by the classical T Tauri star Sz 50, has been discovered.
The Young Population Of The Chamaeleon II Dark Cloud
(2008-06) Spezzi, Loredana; Alcala, Juan M.; Covino, Elvira; Frasca, Antonio; Gandolfi, Davide; Oliveira, Isa; Chapman, Nicholas; Evans, Neal J.; Huard, Tracy L.; Jorgensen, Jes K.; Merin, Bruno; Stapelfeldt, Karl R.; Evans, Neal J.
We discuss the results of the optical spectroscopic follow-up of pre-main-sequence (PMS) objects and candidates selected in the Chamaeleon II dark cloud based on data from the Spitzer Legacy survey "From Molecular Cores to Planet Forming Disks" (c2d) and from previous surveys. Our sample includes both objects with infrared excess selected according to c2d criteria and referred to as young stellar objects and other cloud members and candidates selected from complementary optical and near-infrared data. We characterize the sample of objects by deriving their physical parameters. The vast majority of objects have masses M <= 1 M(circle dot) and ages < 6 Myr. Several of the PMS objects and candidates lie very close to or below the hydrogen-burning limit. A first estimate of the slope of the initial mass function in Cha II is consistent with that of other T associations. The star formation efficiency in the cloud (1%-4%) is consistent with our own estimates for Taurus and Lupus, but significantly lower than for Cha I. This might mean that different star formation activities in the Chamaeleon clouds may reflect a different history of star formation. We also find that the Cha II cloud is turning some 8 M(circle dot) into stars every megayear, which is less than the star formation rate in the other c2d clouds. However, the star formation rate is not steady and evidence is found that the star formation in Cha II might have occurred very rapidly. The H alpha emission of the Cha II PMS objects, as well as possible correlations between their stellar and disk properties, is also investigated.