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RISS 인기검색어
- 검색키워드
- 저자 : Jewitt, David (검색결과 3 건)
- 무료
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FRAGMENTATION KINEMATICS IN COMET 332P/IKEYA-MURAKAMI
Jewitt, David,Mutchler, Max,Weaver, Harold,Hui, Man-To,Agarwal, Jessica,Ishiguro, Masateru,Kleyna, Jan,Li, Jing,Meech, Karen,Micheli, Marco,Wainscoat, Richard,Weryk, Robert American Astronomical Society 2016 ASTROPHYSICAL JOURNAL LETTERS - Vol.829 No.1
<P>We present initial time-resolved observations of the split comet 332P/Ikeya-Murakami taken using the Hubble Space Telescope. Our images reveal a dust-bathed cluster of fragments receding from their parent nucleus at projected speeds in the range 0.06-3.5 m s(-1) from which we estimate ejection times from 2015 October to December. The number of fragments with effective radii greater than or similar to 20 m follows a differential power law with index gamma = -3.6 +/- 0.6, while smaller fragments are less abundant than expected from an extrapolation of this power law. We argue that, in addition to losses due to observational selection, torques from anisotropic outgassing are capable of destroying the small fragments by driving them quickly to rotational instability. Specifically, the spin-up times of fragments. 20 m in radius are shorter than the time elapsed since ejection from the parent nucleus. The effective radius of the parent nucleus is re <= 275 m (geometric albedo 0.04 assumed). This is about seven times smaller than previous estimates and results in a nucleus mass at least 300 times smaller than previously thought. The mass in solid pieces, 2 x 10(9) kg, is about 4% of the mass of the parent nucleus. As a result of its small size, the parent nucleus also has a short spin-up time. Brightness variations in time-resolved nucleus photometry are consistent with rotational instability playing a role in the release of fragments.</P>
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HUBBLE SPACE TELESCOPE INVESTIGATION OF MAIN-BELT COMET 133P/ELST-PIZARRO
Jewitt, David,Ishiguro, Masateru,Weaver, Harold,Agarwal, Jessica,Mutchler, Max,Larson, Steven American Institute of Physics 2014 The Astronomical journal Vol.147 No.5
<P>We report new observations of the prototype main-belt comet (active asteroid) 133P/Elst-Pizarro taken at high angular resolution using the Hubble Space Telescope. The object has three main components: (1) a point-like nucleus; (2) a long, narrow antisolar dust tail; and (3) a short, sunward anti-tail. There is no resolved coma. The nucleus has a mean absolute magnitude H<SUB>V</SUB> = 15.70 ± 0.10 and a light curve range ΔV = 0.42 mag, the latter corresponding to projected dimensions 3.6 × 5.4 km (axis ratio 1.5:1) at the previously measured geometric albedo of 0.05 ± 0.02. We explored a range of continuous and impulsive emission models to simultaneously fit the measured surface brightness profile, width, and position angle of the antisolar tail. Preferred fits invoke protracted emission, over a period of 150 days or less, of dust grains following a differential power-law size distribution with index 3.25 ≤q ≤ 3.5 and with a wide range of sizes. Ultra-low surface brightness dust projected in the sunward direction is a remnant from emission activity occurring in previous orbits, and consists of the largest (≥cm-sized) particles. Ejection velocities of one-micron-sized particles are comparable to the ~1.8 m s<SUP>–1</SUP> gravitational escape speed of the nucleus, while larger particles are released at speeds less than the gravitational escape velocity. The observations are consistent with, but do not prove, a hybrid hypothesis in which mass loss is driven by gas drag from the sublimation of near-surface water ice, but escape is aided by centripetal acceleration from the rotation of the elongated nucleus. No plausible alternative hypothesis has been identified.</P>
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LARGE PARTICLES IN ACTIVE ASTEROID P/2010 A2
Jewitt, David,Ishiguro, Masateru,Agarwal, Jessica IOP Publishing 2013 ASTROPHYSICAL JOURNAL LETTERS - Vol.764 No.1
<P>The previously unknown asteroid P/2010 A2 rose to prominence in 2010 by forming a transient, comet-like tail consisting of ejected dust. The observed dust production was interpreted as the result of either a hypervelocity impact with a smaller body or a rotational disruption. We have re-observed this object, finding that large particles remain a full orbital period after the initial outburst. In the intervening years, particles smaller than similar to 3 mm in radius have been dispersed by radiation pressure, leaving only larger particles in the trail. Since the total mass is dominated by the largest particles, the radiation pressure filtering allows us to obtain a more reliable estimate of the debris mass than was previously possible. We find that the mass contained in the debris is similar to 5 x 10(8) kg (assumed density 3000 kg m(-3)), the ratio of the total debris mass to the nucleus mass is similar to 0.1, and that events like P/2010 A2 contribute <3% to the Zodiacal dust production rate. Physical properties of the nucleus and debris are also determined.</P>
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