Browsing by Author "Carpenter, J. M."

Now showing 1 - 4 of 4
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    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 Tuscaloosa
    We 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.
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    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 Tuscaloosa
    We 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.
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    Multi-wavelength modeling of the spatially resolved debris disk of HD107146
    (EDP Sciences, 2001-09-15) Ertel, S.; Wolf, S.; Metchev, S.; Schneider, G.; Carpenter, J. M.; Meyer, M. R.; Hillenbrand, L. A.; Silverstone, M. D.; University of Kiel; State University of New York (SUNY) System; State University of New York (SUNY) Stony Brook; University of Arizona; California Institute of Technology; Swiss Federal Institutes of Technology Domain; ETH Zurich; University of Alabama Tuscaloosa
    Aims. We aim to constrain the location, composition, and dynamical state of planetesimal populations and dust around the young, sun-like (G2V) star HD107146. Methods. We consider coronagraphic observations obtained with the Advanced Camera for Surveys (HST/ACS) onboard the Hubble Space Telescope (HST) in broad V (lambda(c) approximate to 0.6 mu m) and broad I (lambda(c) approximate to 0.8 mu m) filters, a resolved 1.3 mm map obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA), Spitzer/IRS low resolution spectra in the range of 7.6 mu m to 37.0 mu m, and the spectral energy distribution (SED) of the object at wavelengths ranging from 3.5 mu m to 3.1 mm. We complement these data with new coronagraphic high resolution observations of the debris disk using the Near Infrared Camera and Multi-Object Spectrometer (HST/NICMOS) aboard the HST in the F110W filter (lambda(c) approximate to 1.1 mu m). The SED and images of the disk in scattered light as well as in thermal reemission are combined in our modeling using a parameterized model for the disk density distribution and optical properties of the dust. Results. A detailed analytical model of the debris disk around HD107146 is presented that allows us to reproduce the almost entire set of spatially resolved and unresolved multi-wavelength observations. Considering the variety of complementary observational data, we are able to break the degeneracies produced by modeling SED data alone. We find the disk to be an extended ring with a peak surface density at 131 AU. Furthermore, we find evidence for an additional, inner disk probably composed of small grains released at the inner edge of the outer disk and moving inwards due to Poynting-Robertson drag. A birth ring scenario (i.e., a more or less broad ring of planetesimals creating the dust disk trough collisions) is found to be the most likely explanation of the ringlike shape of the disk.
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    STRUCTURE AND COMPOSITION OF TWO TRANSITIONAL CIRCUMSTELLAR DISKS IN CORONA AUSTRALIS
    (IOP Publishing, 2010-08-13) Hughes, A. M.; Andrews, S. M.; Wilner, D. J.; Meyer, M. R.; Carpenter, J. M.; Qi, C.; Hales, A. S.; Casassus, S.; Hogerheijde, M. R.; Mamajek, E. E.; Wolf, S.; Henning, T.; Silverstone, M. D.; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; Swiss Federal Institutes of Technology Domain; ETH Zurich; California Institute of Technology; National Radio Astronomy Observatory (NRAO); Universidad de Chile; Leiden University; Leiden University - Excl LUMC; University of Rochester; University of Kiel; Max Planck Society; Eureka Scientific; University of Alabama Tuscaloosa
    The late stages of evolution of the primordial circumstellar disks surrounding young stars are poorly understood, yet vital to constraining theories of planet formation. We consider basic structural models for the disks around two similar to 10 Myr old members of the nearby RCrA association: RX J1842.9-3532 and RX J1852.3-3700. We present new arc second-resolution maps of their 230 GHz continuum emission from the Submillimeter Array and unresolved CO(3-2) spectra from the Atacama Submillimeter Telescope Experiment. By combining these data with broadband fluxes from the literature and infrared fluxes and spectra from the catalog of the Formation and Evolution of Planetary Systems Legacy program on the Spitzer Space Telescope, we assemble a multiwavelength data set probing the gas and dust disks. Using the Monte Carlo radiative transfer code RADMC to model simultaneously the spectral energy distribution and millimeter continuum visibilities, we derive basic dust disk properties and identify an inner cavity of radius 16 AU in the disk around RX J1852.3-3700. We also identify an optically thin 5 AU cavity in the disk around RX J1842.9-3532, with a small amount of optically thick material close to the star. The molecular line observations suggest an intermediate disk inclination in RX J1842.9-3532, consistent with the continuum emission. In combination with the dust models, the molecular data allow us to derive a lower CO content than expected, suggesting that the process of gas clearing is likely underway in both systems, perhaps simultaneously with planet formation.