Browsing by Author "Hines, D. C."
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Item Evolution of mid-infrared excess around sun-like stars: constraints on models of terrestrial planet formation(IOP Publishing, 2008-01-09) Meyer, M. R.; Carpenter, J. M.; Mamajek, E. E.; Hillenbrand, L. A.; Hollenbach, D.; Moro-Martin, A.; Kim, J. S.; Silverstone, M. D.; Najita, J.; Hines, D. C.; Pascucci, I.; Stauffer, J. R.; Bouwman, J.; Backman, D. E.; University of Arizona; California Institute of Technology; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; National Aeronautics & Space Administration (NASA); NASA Ames Research Center; Princeton University; National Optical Astronomy Observatory; Max Planck Society; University of Alabama TuscaloosaWe report observations from the Spitzer Space Telescope regarding the frequency of 24 mm excess emission toward Sun-like stars. Our unbiased sample is composed of 309 stars with masses 0.7-2.2 M-circle dot and ages from, < 3 Myr to > 3 Gyr that lack excess emission at wavelengths <= 8 mu m. We identify 30 stars that exhibit clear evidence of excess emission from the observed 24 mu m/8 mu m flux ratio. The implied 24 mu m excesses of these candidate debris disk systems range from 13% (the minimum detectable) to more than 100% compared to the expected photospheric emission. The frequency of systems with evidence for dust debris emitting at 24 mu m ranges from 8.5%-19% at ages < 300 Myr to < 4% for older stars. The results suggest that many, perhaps most, Sun-like stars might form terrestrial planets.Item Formation and evolution of planetary systems: Upper limits to the gas mass in disks around Sun-like stars(IOP Publishing, 2006-11-10) Pascucci, I.; Gorti, U.; Hollenbach, D.; Najita, J.; Meyer, M. R.; Carpenter, J. M.; Hillenbrand, L. A.; Herczeg, G. J.; Padgett, D. L.; Mamajek, E. E.; Silverstone, M. D.; Schlingman, W. M.; Kim, J. S.; Stobie, E. B.; Bouwman, J.; Wolf, S.; Rodmann, J.; Hines, D. C.; Lunine, J.; Malhotra, R.; University of Arizona; University of California System; University of California Berkeley; National Aeronautics & Space Administration (NASA); NASA Ames Research Center; National Optical Astronomy Observatory; California Institute of Technology; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; Max Planck Society; University of Alabama TuscaloosaWe have carried out a sensitive search for gas emission lines at IR and millimeter wavelengths for a sample of 15 young Sun-like stars selected from our dust disk survey with Spitzer. We have used mid-IR lines to trace the warm (300-100 K) gas in the inner disk and millimeter transitions of (CO)-C-12 to probe the cold (similar to 20 K) outer disk. We report no gas line detections from our sample. Line flux upper limits are first converted to warm and cold gas mass limits using simple approximations allowing a direct comparison with values from the literature. We also present results from more sophisticated models following Gorti & Hollenbach that confirm and extend our simple analysis. These models show that the [S-I]25.23 mu m line can set constraining limits on the gas surface density at the disk inner radius and traces disk regions up to a few AU. We find that none of the 15 systems have more than 0.04M(J) of gas within a few AU from the disk inner radius for disk radii from 1 to similar to 40 AU. These gas mass upper limits even in the eight systems younger than similar to 30 Myr suggest that most of the gas is dispersed early. The gas mass upper limits in the 10-40 AU region, which is mainly traced by our CO data, are < 2 M-circle plus. If these systems are analogs of the solar system, they either have already formed Uranus- and Neptune-like planets or will not form them beyond 100 Myr. Finally, the gas surface density upper limits at 1 AU are smaller than 0.01% of the minimum mass solar nebula for most of the sources. If terrestrial planets form frequently and their orbits are circularized by gas, then circularization occurs early.Item Probing dust grain evolution in IM Lupi's circumstellar disc - Multi-wavelength observations and modelling of the dust disc(EDP Sciences, 2008-08-08) 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.; University of Exeter; Centre National de la Recherche Scientifique (CNRS); UDICE-French Research Universities; Communaute Universite Grenoble Alpes; Universite Grenoble Alpes (UGA); California Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Jet Propulsion Laboratory (JPL); University of Arizona; Leiden University; Leiden University - Excl LUMC; University of California System; University of California Berkeley; University of California Los Angeles; University of Texas System; University of Texas Austin; Max Planck Society; Eureka Scientific; University of Kiel; University of Alabama TuscaloosaAims. 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.