Browsing by Author "Hillenbrand, L. A."

Now showing 1 - 4 of 4
  • Thumbnail Image
    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 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.
  • Thumbnail Image
    Item
    The formation and evolution of planetary systems : Grain growth and chemical processing of dust in T Tauri systems
    (IOP Publishing, 2008-08-10) Bouwman, J.; Henning, Th.; Hillenbrand, L. A.; Meyer, M. R.; Pascucci, I.; Carpenter, J.; Hines, D.; Kim, J. S.; Silverstone, M. D.; Hollenbach, D.; Wolf, S.; Max Planck Society; California Institute of Technology; University of Arizona; National Aeronautics & Space Administration (NASA); NASA Ames Research Center; University of Alabama Tuscaloosa
    This paper is one in a series presenting results obtained within the Formation and Evolution of Planetary Systems (FEPS) Legacy Science Program on the Spitzer Space Telescope. Here we present a study of dust processing and growth in seven protoplanetary disks. Our spectra indicate that the circumstellar silicate dust grains have grown to sizes at least 10 times larger than observed in the interstellar medium and show evidence for a non-negligible (similar to 5% in mass fractions) contribution from crystalline species. These results are similar to those of other studies of protoplanetary disks. In addition, we find a correlation between the strength of the amorphous silicate feature and the shape of the spectral energy distribution. This latter result is consistent with the growth and subsequent gravitational settling of dust grains toward the disk midplane. Furthermore, we find a change in the relative abundance of the different crystalline species: more enstatite than forsterite is observed in the inner warm dust population at similar to 1 AU, while forsterite dominates in the colder outer regions at similar to 5-15 AU. This change in the relative abundances argues for a localized crystallization process rather than a radial mixing scenario in which crystalline silicates are being transported outwards from a single formation region in the hot inner parts of the disk. Finally, we report the detection of emission from polycyclic aromatic hydrocarbon ( PAH) molecules in five out of seven sources. We find a tentative PAH band at 8.2 mu m that was previously undetected in the spectra of disks around low-mass pre-main-sequence stars.
  • Thumbnail Image
    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 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.
  • Thumbnail Image
    Item
    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.