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7. CURVED WALLS: GRAIN GROWTH, SETTLING, AND COMPOSITION PATTERNS IN T TAURI DISK DUST SUBLIMATION FRONTS.

Author

McClure, M. K., D'Alessio, P., Calvet, N., Espaillat, C., Hartmann, L., Sargent, B., Watson, D. M., Ingleby, L., and Hernández, J.

Subjects
METEORITES, METEORS, METEOROIDS, PROTOPLANETARY disks, T Tauri stars, HERBIG Ae/Be stars
Abstract

The dust sublimation walls of disks around T Tauri stars represent a directly observable cross-section through the disk atmosphere and midplane. Their emission properties can probe the grain size distribution and composition of the innermost regions of the disk, where terrestrial planets form. Here we calculate the inner dust sublimation wall properties for four classical T Tauri stars with a narrow range of spectral types and inclination angles and a wide range of mass accretion rates to determine the extent to which the walls are radially curved. Best fits to the near- and mid-IR excesses are found for curved, two-layer walls in which the lower layer contains larger, hotter, amorphous pyroxene grains with Mg/(Mg+Fe) = 0.6 and the upper layer contains submicron, cooler, mixed amorphous olivine and forsterite grains. As the mass accretion rates decrease from 10–8 to 10–10M☼ yr–1, the maximum grain size in the lower layer decreases from ∼3 to 0.5 μm. We attribute this to a decrease in fragmentation and turbulent support for micron-sized grains with decreasing viscous heating. The atmosphere of these disks is depleted of dust with dust-gas mass ratios 1 × 10–4 of the interstellar medium (ISM) value, while the midplane is enhanced to eight times the ISM value. For all accretion rates, the wall contributes at least half of the flux in the optically thin 10 μm silicate feature. Finally, we find evidence for an iron gradient in the disk, suggestive of that found in our solar system. [ABSTRACT FROM AUTHOR]

Published
2013
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8. CHARACTERIZING THE STELLAR PHOTOSPHERES AND NEAR-INFRARED EXCESSES IN ACCRETING T TAURI SYSTEMS.

Author

MCCLURE, M. K., CALVET, N., ESPAILLAT, C., HARTMANN, L., HERNÁNDEZ, J., INGLEBY, L., LUHMAN, K. L., D'ALESSIO, P., and SARGENT, B.

Subjects
STELLAR photospheres, NEAR infrared radiation, INFRARED telescopes, ACCRETION (Astrophysics), SOLAR flares, DWARF stars
Abstract

Using NASA Infrared Telescope Facility SpeX data from 0.8 to 4.5µm, we determine self-consistently the stellar properties and excess emission above the photosphere for a sample of classical T Tauri stars (CTTS) in the Taurus molecular cloud with varying degrees of accretion. This process uses a combination of techniques from the recent literature as well as observations of weak-line T Tauri stars to account for the differences in surface gravity and chromospheric activity between the T Tauri stars and dwarfs, which are typically used as photospheric templates for CTTS. Our improved veiling and extinction estimates for our targets allow us to extract flux-calibrated spectra of the excess in the near-infrared.We find that we are able to produce an acceptable parametric fit to the near-infrared excesses using a combination of up to three blackbodies. In half of our sample, two blackbodies at temperatures of 8000 K and 1600 K suffice. These temperatures and the corresponding solid angles are consistent with emission from the accretion shock on the stellar surface and the inner dust sublimation rim of the disk, respectively. In contrast, the other half requires three blackbodies at 8000, 1800, and 800 K, to describe the excess. We interpret the combined two cooler blackbodies as the dust sublimation wall with either a contribution from the disk surface beyond the wall or curvature of the wall itself, neither of which should have single-temperature blackbody emission. In these fits, we find no evidence of a contribution from optically thick gas inside the inner dust rim. [ABSTRACT FROM AUTHOR]

Published
2013
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13. Keck Interferometer Observations of FU Orionis Objects.

Author

Millan-Gabet, R., Monnier, J. D., Akeson, R. L., Hartmann, L., Berger, J.-P., Tannirkulam, A., Melnikov, S., Billmeier, R., Calvet, N., D’Alessio, P., Hillenbrand, L. A., Kuchner, M., Traub, W. A., Tuthill, P. G., Beichman, C., Boden, A., Booth, A., Colavita, M., Creech-Eakman, M., and Gathright, J.

Published
2006
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19. Deep 10 and 18 Micron Imaging of the HR 4796A Circumstellar Disk: Transient Dust Particles and Tentative Evidence for a Brightness AsymmetryBased on observations at the W. M. Keck Observatory, which is operated as a scientific partnership between Caltech, the University of California, and NASA, and made possible by the generous financial support of the W. M. Keck Foundation.

Author

Telesco, C. M., Fisher, R. S., Piña, R. K., Knacke, R. F., Dermott, S. F., Wyatt, M. C., Grogan, K., Holmes, E. K., Ghez, A. M., Prato, L., Hartmann, L. W., and Jayawardhana, R.

Published
2000
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45. The 24 Micron View of Embedded Star Formation in NGC 7129.

Author

Muzerolle, J., Megeath, S. T., Gutermuth, R. A., Allen, L. E., Pipher, J. L., Hartmann, L., Gordon, K. D., Padgett, D. L., Noriega-Crespo, A., Myers, P. C., Fazio, G. G., Rieke, G. H., Young, E. T., Morrison, J. E., Hines, D. C., Su, K. Y. L., Engelbracht, C. W., and Misselt, K. A.

Published
2004
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