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- 검색키워드
- 저자 : Wainscoat, Richard J. (검색결과 2 건)
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OBSERVATIONAL AND DYNAMICAL CHARACTERIZATION OF MAIN-BELT COMET P/2010 R2 (La Sagra)
Hsieh, Henry H.,Yang, Bin,Haghighipour, Nader,Novaković,, Bojan,Jedicke, Robert,Wainscoat, Richard J.,Denneau, Larry,Abe, Shinsuke,Chen, Wen-Ping,Fitzsimmons, Alan,Granvik, Mikael,Grav, Tommy,Ip, American Institute of Physics 2012 The Astronomical journal Vol.143 No.5
<P>We present observations of the recently discovered comet-like main-belt object P/2010 R2 (La Sagra) obtained by Pan-STARRS1 and the Faulkes Telescope-North on Haleakala in Hawaii, the University of Hawaii 2.2 m, Gemini-North, and Keck I telescopes on Mauna Kea, the Danish 1.54 m telescope (operated by the MiNDSTEp consortium) at La Silla, and the Isaac Newton Telescope on La Palma. An antisolar dust tail is observed to be present from 2010 August through 2011 February, while a dust trail aligned with the object's orbit plane is also observed from 2010 December through 2011 August. Assuming typical phase darkening behavior, P/La Sagra is seen to increase in brightness by >1 mag between 2010 August and December, suggesting that dust production is ongoing over this period. These results strongly suggest that the observed activity is cometary in nature (i.e., driven by the sublimation of volatile material), and that P/La Sagra is therefore the most recent main-belt comet to be discovered. We find an approximate absolute magnitude for the nucleus of H<SUB>R</SUB> = 17.9 ± 0.2 mag, corresponding to a nucleus radius of ~0.7 km, assuming an albedo of p = 0.05. Comparing the observed scattering surface areas of the dust coma to that of the nucleus when P/La Sagra was active, we find dust-to-nucleus area ratios of A<SUB>d</SUB>/A<SUB>N</SUB> = 30-60, comparable to those computed for fellow main-belt comets 238P/Read and P/2008 R1 (Garradd), and one to two orders of magnitude larger than for two other main-belt comets (133P/Elst-Pizarro and 176P/LINEAR). Using optical spectroscopy to search for CN emission, we do not detect any conclusive evidence of sublimation products (i.e., gas emission), finding an upper limit CN production rate of Q<SUB>CN</SUB> < 6 × 10<SUP>23</SUP> mol s<SUP>–1</SUP>, from which we infer an H<SUB>2</SUB>O production rate of <img SRC='http://ej.iop.org/images/1538-3881/143/5/104/aj423523ieqn1.gif' ALIGN='MIDDLE' ALT='$Q_{\rm H_2O}\,{<}\,10^{26}$'/> mol s<SUP>–1</SUP>. Numerical simulations indicate that P/La Sagra is dynamically stable for >100 Myr, suggesting that it is likely native to its current location and that its composition is likely representative of other objects in the same region of the main belt, though the relatively close proximity of the 13:6 mean-motion resonance with Jupiter and the (3,–2,–1) three-body mean-motion resonance with Jupiter and Saturn mean that dynamical instability on larger timescales cannot be ruled out.</P>
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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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