HUBBLE AND SPITZER SPACE TELESCOPE OBSERVATIONS OF THE DEBRIS DISK AROUND THE NEARBY K DWARF HD 92945

Journal Article · Fri Jul 15 00:00:00 EDT 2011 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/142/1/30· OSTI ID:21583048

Golimowski, D A; Chen, C H ^[1]; Krist, J E; Stapelfeldt, K R; Bryden, G ^[2]; Ardila, D R ^[3]; Clampin, M ^[4]; Ford, H C ^[5]; Illingworth, G D ^[6]; Plavchan, P ^[7]; Rieke, G H; Su, K Y. L. ^[8]

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1. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
3. NASA Herschel Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)
4. NASA Goddard Space Flight Center, Code 681, Greenbelt, MD 20771 (United States)
5. Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218 (United States)
6. Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States)
7. NASA Exoplanet Science Institute, California Institute of Technology, Pasadena, CA 91106 (United States)
8. Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

We present the first resolved images of the debris disk around the nearby K dwarf HD 92945, obtained with the Hubble Space Telescope's (HST 's) Advanced Camera for Surveys. Our F606W (Broad V) and F814W (Broad I) coronagraphic images reveal an inclined, axisymmetric disk consisting of an inner ring about 2.''0-3.''0 (43-65 AU) from the star and an extended outer disk whose surface brightness declines slowly with increasing radius approximately 3.''0-5.''1 (65-110 AU) from the star. A precipitous drop in the surface brightness beyond 110 AU suggests that the outer disk is truncated at that distance. The radial surface-density profile is peaked at both the inner ring and the outer edge of the disk. The dust in the outer disk scatters neutrally but isotropically, and it has a low V-band albedo of 0.1. This combination of axisymmetry, ringed and extended morphology, and isotropic neutral scattering is unique among the 16 debris disks currently resolved in scattered light. We also present new infrared photometry and spectra of HD 92945 obtained with the Spitzer Space Telescope's Multiband Imaging Photometer and InfraRed Spectrograph. These data reveal no infrared excess from the disk shortward of 30 {mu}m and constrain the width of the 70 {mu}m source to {approx}<180 AU. Assuming that the dust comprises compact grains of astronomical silicate with a surface-density profile described by our scattered-light model of the disk, we successfully model the 24-350 {mu}m emission with a minimum grain size of a{sub min} = 4.5 {mu}m and a size distribution proportional to a {sup -3.7} throughout the disk, but with maximum grain sizes of 900 {mu}m in the inner ring and 50 {mu}m in the outer disk. Together, our HST and Spitzer observations indicate a total dust mass of {approx}0.001M{sub +}. However, our observations provide contradictory evidence of the dust's physical characteristics: its neutral V-I color and lack of 24 {mu}m emission imply grains larger than a few microns, but its isotropic scattering and low albedo suggest a large population of submicron-sized grains. If grains smaller than a few microns are absent, then stellar radiation pressure may be the cause only if the dust is composed of highly absorptive materials like graphite. The dynamical causes of the sharply edged inner ring and outer disk are unclear, but recent models of dust creation and transport in the presence of migrating planets support the notion that the disk indicates an advanced state of planet formation around HD 92945.

• OSTI ID: 21583048
• Journal Information: Astronomical Journal (New York, N.Y. Online), Vol. 142, Issue 1; Other Information: DOI: 10.1088/0004-6256/142/1/30; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ALBEDO
ASTROPHYSICS
AXIAL SYMMETRY
BRIGHTNESS
CAMERAS
COLOR
DUSTS
EMISSION
GRAIN SIZE
GRAPHITE
IMAGES
MORPHOLOGY
PHOTOMETERS
PHOTOMETRY
PLANETS
PROTOPLANETS
SILICATES
STARS
STELLAR RADIATION
TELESCOPES
CARBON
ELEMENTS
MEASURING INSTRUMENTS
MICROSTRUCTURE
MINERALS
NONMETALS
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PHYSICS
RADIATIONS
SILICON COMPOUNDS
SIZE
SYMMETRY