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تسجيل مستخدم جديدExtending the Model of KH 15D: Estimating the Effects of Forward Scattering and Curvature of the Occulting Ring Edge
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The periodic eclipses of the pre-main-sequence binary, KH 15D, have been explained by a circumbinary dust ring inclined to the orbital plane, which causes occultations of the stars as they pass behind the ring edge. We compute the extinction and forward scattering of light by the edge of the dust ring to explain (1) the gradual slope directly preceding total eclipse, (2) the gradual decline at the end of ingress, and (3) the slight rise in flux at mid-eclipse. The size of the forward scattering halo indicates that the dust grains have a radius of a ~ 6 (D/3 AU) microns, where D is the distance of the edge of the ring from the system barycenter. This dust size estimate agrees well with estimates of the dust grain size from polarimetry, adding to the evidence that the ring lies at several AU. Finally, the ratio of the fluxes inside and outside eclipse independently indicates that the ring lies at a few astronomical units.
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Following two years of complete occultation of both stars by its opaque circumbinary ring, the binary T Tauri star KH 15D has abruptly brightened again during apastron phases, reaching I = 15 mag. Here, we show that the brightening is accompanied by
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We examine the light and color evolution of the T Tauri binary KH 15D through photometry obtained at wavelengths between 0.55 and 8.0 $mu$m. The data were collected with ANDICAM on the 1.3 m SMARTS telescope at Cerro-Tololo Inter-American Observatory
and with IRAC on the Spitzer Space Telescope. We show that the systems circumbinary ring, which acts as a screen that covers and uncovers different portions of the binary orbit as the ring precesses, has reached an orientation where the brighter component (star B) fully or nearly fully emerges during each orbital cycle. The fainter component (star A) remains fully occulted by the screen at all phases. The leading and trailing edges of the screen move across the sky at the same rate of $sim$15 meters per second, consistent with expectation for a ring with a radius and width of $sim$4 AU and a precession period of $sim$6500 years. Light and color variations continue to indicate that the screen is sharp edged and opaque at emph{VRIJH} wavelengths. However, we find an increasing transparency of the ring edge at 2.2, 3.6, and 4.5 $mu$m. Reddening seen at the beginning of the eclipse that occurred during the CSI 2264 campaign particularly suggests selective extinction by a population of large dust grains. Meanwhile, the gradual bluing observed while star B is setting is indicative of forward scattering effects at the edge of the ring. The SED of the system at its bright phase shows no evidence of infrared excess emission that can be attributed to radiation from the ring or other dust component out to 8 microns.
KH 15D is a well-known spectroscopic binary because of its unique and dramatic photometric variability. The variability is explained by a circumbinary dust ring but the ring itself was never directly detected. We present a new interpretation of the d
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