Image from CfA press release 03-19, credit: P. Garnavich.
| KH
15D
is an unusual variable star in the young cluster NGC 2264. It shows a
48-day period featuring stellar eclipses that have varied in depth and
shape over the past century (Kearns
& Herbst 1998; Winn
et al. 2003; Johnson
& Winn 2004). The latest theories propose that the
object is a
pre-main sequence binary system surrounded by a precessing
circumbinary disk inclined to our line of sight (Winn
et al. 2004; Chiang
& Murray-Clay 2004). This disk blocks out
various portions of the binary orbits at various epochs. Such a circumbinary disk should scatter and polarize incident starlight as well as absorbing it. This effect could explain the brightness of KH 15D at its current mid-eclipse phase, when both stars are thought to be occulted by the disk (Winn et al. 2006). A key question unresolved in this scenario is: where are the scattering regions in the system? Detailed polarimetric observations of the KH 15D (extending the work of Agol et al. 2004) can help distinguish between models of the circumstellar and circumbinary material. At the Protostars and Planets V meeting in 2005, I presented new polarimetric data taken by Gary Schmidt at U. Arizona that suggest the polarized flux from KH 15D may be constant over the binary cycle, implying that the scattering regions are not eclipsed by the disk. See the PPV poster for more details. |
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| In this poster, I also
presented radiative transfer models of the “nebula” and “disk
atmosphere” scattering scenarios proposed by Winn et al. 2006, finding that the two cases
can be distinguished polarimetrically only during the flux
eclipse. I am currently working with Christopher
M. Johns-Krull at Rice U. and Alexei V. Filippenko at UC Berkeley to
plan further polarimetric observations of KH 15D that will fill in the
polarized light curve and help constrain system models. I previously collaborated with Eric B. Ford and Eugene I. Chiang at UC Berkeley on constructing simpler models of the scattered light within the KH 15D system. We presented a poster at the January 2005 AAS meeting showing that the direct and polarized light levels seen at mid-eclipse are best reproduced by a model in which light reaches us by scattering through the disk rather than reflecting off the disk face. |
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| The images below are early flux and polarization disk
models by JLH. The disk has an opening angle of 10 degrees, and
scattering is by electrons only. Green and red regions represent light
originating, respectively, from a central star and a second star with a
small vertical offset. |
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