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Title: HUBBLE SPACE TELESCOPE PRE-PERIHELION ACS/WFC IMAGING POLARIMETRY OF COMET ISON (C/2012 S1) AT 3.81 AU

We present polarization images of Comet ISON (C/2012 S1) taken with the Hubble Space Telescope (HST) on UTC 2013 May 8 (r {sub h} = 3.81 AU, Δ = 4.34 AU), when the phase angle was α ≈ 12.°16. This phase angle is approximately centered in the negative polarization branch for cometary dust. The region beyond 1000 km (∼0.32 arcsec ≈ 6 pixels) from the nucleus shows a negative polarization amplitude of p% ∼ –1.6%. Within 1000 km of the nucleus, the polarization position angle rotates to be approximately perpendicular to the scattering plane, with an amplitude p% ∼ +2.5%. Such positive polarization has been observed previously as a characteristic feature of cometary jets, and we show that Comet ISON does indeed harbor a jet-like feature. These HST observations of Comet ISON represent the first visible light, imaging polarimetry with subarcsecond spatial resolution of a Nearly Isotropic Comet beyond 3.8 AU from the Sun at a small phase angle. The observations provide an early glimpse of the properties of the cometary dust preserved in this Oort-Cloud comet.
Authors:
; ;  [1] ; ; ;  [2] ; ;  [3] ; ;  [4] ;  [5] ;  [6]
  1. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
  2. Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States)
  3. Department of Physics, P.O. Box 64, FI-00014 University of Helsinki (Finland)
  4. Astronomical Institute of V. N. Karazin University, Kharkov, 61058 (Ukraine)
  5. Lowell Observatory, Flagstaff, AZ 86001 (United States)
  6. Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723 (United States)
Publication Date:
OSTI Identifier:
22364045
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 780; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; ASTROPHYSICS; COMETS; COSMIC DUST; JETS; POLARIMETERS; POLARIMETRY; POLARIZATION; SCATTERING; SPACE; SPATIAL RESOLUTION; SUN; TELESCOPES; TRITIUM; VISIBLE RADIATION