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Investigating the circumstellar environments of young stars with the PROMPT polarimeter

University of North Carolina at Chapel Hill. Library
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  • Design


We have designed and built a prototype imaging polarimeter for use on the PROMPT robotic telescopes located at the Cerro Tololo International Observatory. The polarimeter uses a Fresnel rhomb and wollaston prism to image two orthogonal polarization states onto a single CCD chip, with an image field of view of 10x4.5 arcmin. Using the polarimeter, we have investigated the circumstellar regions of 11 Herbig Ae/Be stars, and done extensive follow-up observations of 3 stars of interest: KK Oph, a well-studied star with previously limited polarimetric data; NX Pup, a star known to vary photometrically but with previously unknown polarimetric variability; and SS7344, a star with very limited previous photometric data and no prior polarimetric data. We have found polarimetric and photometric variations in KK Oph and NX Pup that are consistent with models of dust obscuration. Both KK Oph and NX Pup show an increase in polarization accompanied by a decrease in visual magnitude and a reddening. However, neither star shows the blueing at deep minima and maximum polarization characteristic of the UXor classification of stars. We have demonstrated that SS7344 has an intrinsic polarization, but does not display the photometric and polarimetric variations expected from a young star with an evolving circumstellar environment, indicating that this object either has a disk seen in an orientation that has little inclination, or one with no appreciable puffed-up inner rim.

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