113 research outputs found
Dusty Planetary Systems
Extensive photometric stellar surveys show that many main sequence stars show
emission at infrared and longer wavelengths that is in excess of the stellar
photosphere; this emission is thought to arise from circumstellar dust. The
presence of dust disks is confirmed by spatially resolved imaging at infrared
to millimeter wavelengths (tracing the dust thermal emission), and at optical
to near infrared wavelengths (tracing the dust scattered light). Because the
expected lifetime of these dust particles is much shorter than the age of the
stars (>10 Myr), it is inferred that this solid material not primordial, i.e.
the remaining from the placental cloud of gas and dust where the star was born,
but instead is replenished by dust-producing planetesimals. These planetesimals
are analogous to the asteroids, comets and Kuiper Belt objects (KBOs) in our
Solar system that produce the interplanetary dust that gives rise to the
zodiacal light (tracing the inner component of the Solar system debris disk).
The presence of these "debris disks" around stars with a wide range of masses,
luminosities, and metallicities, with and without binary companions, is
evidence that planetesimal formation is a robust process that can take place
under a wide range of conditions. This chapter is divided in two parts. Part I
discusses how the study of the Solar system debris disk and the study of debris
disks around other stars can help us learn about the formation, evolution and
diversity of planetary systems by shedding light on the frequency and timing of
planetesimal formation, the location and physical properties of the
planetesimals, the presence of long-period planets, and the dynamical and
collisional evolution of the system. Part II reviews the physical processes
that affect dust particles in the gas-free environment of a debris disk and
their effect on the dust particle size and spatial distribution.Comment: 68 pages, 25 figures. To be published in "Solar and Planetary
Systems" (P. Kalas and L. French, Eds.), Volume 3 of the series "Planets,
Stars and Stellar Systems" (T.D. Oswalt, Editor-in-chief), Springer 201
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The albedo, size, and density of binary Kuiper Belt object (47171) 1999 TC36
We measured the system-integrated thermal emission of the binary Kuiper Belt object (47171 ) 1999 TC36, at wavelengths near 24 and 70 μm using the Spitzer Space Telescope. We fit these data and the visual magnitude using both the standard thermal model and thermophysical models. We find that the effective diameter of the binary is 405 km, with a range of 350-470 km, and the effective visible geometric albedo for the system is 0.079, with a range of 0.055-0.11. The binary orbit, magnitude contrast between the components, and system mass have been determined from HSTdata studied by Margot et al. Our effective diameter, combined with that system mass, indicates an average density for the objects of 0.5 g cm-3, with a range 0.3-0.8 g cm -3. This density is low compared to that of materials expected to be abundant in solid bodies in the trans-Neptunian region, requiring 50%-75% of the interior of (47171 ) 1999 TC36 be taken up by void space. This conclusion is not greatly affected if (47171)1999 TC36 is "differentiated" (in the sense of having either a rocky or just a nonporous core). If the primary is itself a binary, the average density of that (hypothetical) triple system would be in the range 0.4-1.l g cm -3, with a porosity in the range 15%-70%. © 2006. The American Astronomical Society. All rights reserved
PRECISE MEASUREMENT OF THE TAU LIFETIME*
We have measured the r lifetime with the Mark II Vertex Detector at PEP. We find rr = (3.20 f 0.41 f.35) x lo-l3 set, which agrees well with e- p- r universality
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Test of QED to fourth order by study of four-lepton final states in e+e- interactions at 29 GeV with the Mark II detector.
We have tested QED to fourth order in the coupling constant in the large-Q2 region by studying four-lepton final states in e+e- interactions with the Mark II detector at the SLAC storage ring PEP (s=29 GeV). All four final-state particles were detected at large angles with respect to the beam axis. For an integrated luminosity of 205 pb-1, we observed ten e+e-e+e-, ten e+e-+-, and one events with opposite-charge pair masses greater than 1 GeV/c2. These events show good agreement with the complete 4 QED calculation. © 1990 The American Physical Society
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Test of QED to fourth order by study of four-lepton final states in e+e- interactions at 29 GeV with the Mark II detector.
We have tested QED to fourth order in the coupling constant in the large-Q2 region by studying four-lepton final states in e+e- interactions with the Mark II detector at the SLAC storage ring PEP (s=29 GeV). All four final-state particles were detected at large angles with respect to the beam axis. For an integrated luminosity of 205 pb-1, we observed ten e+e-e+e-, ten e+e-+-, and one events with opposite-charge pair masses greater than 1 GeV/c2. These events show good agreement with the complete 4 QED calculation. © 1990 The American Physical Society
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Inclusive charged hadron and K0 production in two-photon interactions
The inclusive transverse momentum distributions of charged hadrons and K0's produced in tagged photon-photon collisions, are measured and compared to model calculations up to a pT of 5 GeV/c. The relative abundance of K0's favor the inclusion of charm. © 1993
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Inclusive charged hadron and K0 production in two-photon interactions
The inclusive transverse momentum distributions of charged hadrons and K 's produced in tagged photon-photon collisions, are measured and compared to model calculations up to a p of 5 GeV/c. The relative abundance of K 's favor the inclusion of charm. © 1993. 0 0
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Refined measurement of the B-hadron lifetime.
We report a new measurement of the average lifetime of hadrons containing bottom quarks. The B-hadron decays are tagged by identifying leptons at high transverse momentum. From a fit to the lepton impact-parameter distribution, the average B-hadron lifetime is found to be (0.98 0.12 0.13)×10-12 sec. © 1989 The American Physical Society
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