Hubble and spitzer space telescope observations of the debris disk around the nearby K dwarf HD92945

D. A. Golimowski, J. E. Krist, K. R. Stapelfeldt, C. H. Chen, D. R. Ardila, G. Bryden, M. Clampin, H. C. Ford, G. D. Illingworth, P. Plavchan, G. H. Rieke, K. Y.L. Su

Research output: Contribution to journalArticlepeer-review

51 Scopus citations

Abstract

We present the first resolved images of the debris disk around the nearby K dwarf HD92945, 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 20-30 (43-65AU) from the star and an extended outer disk whose surface brightness declines slowly with increasing radius approximately 30-51 (65-110AU) from the star. A precipitous drop in the surface brightness beyond 110AU 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 HD92945 obtained with the Spitzer Space Telescope's Multiband Imaging Photometer and InfraRed Spectrograph. These data reveal no infrared excess from the disk shortward of 30μm and constrain the width of the 70μm source to ≲180AU. 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 24-350μm emission with a minimum grain size of a min = 4.5μm and a size distribution proportional to a -3.7 throughout the disk, but with maximum grain sizes of 900μm in the inner ring and 50μm in the outer disk. Together, our HST and Spitzer observations indicate a total dust mass of ∼0.001M . However, our observations provide contradictory evidence of the dust's physical characteristics: its neutral V-I color and lack of 24μm 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 HD92945.

Original languageEnglish (US)
Article number30
JournalAstronomical Journal
Volume142
Issue number1
DOIs
StatePublished - Jul 2011

Keywords

  • circumstellar matter
  • infrared: planetary systems
  • planet-disk interactions
  • planetary systems
  • protoplanetary disks
  • stars: individual (HD 92945)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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