Anomalous Polarization of the Gamma Ophiuchi Debris Disk

Details Anomalous Polarization of the Gamma Ophiuchi Debris Disk Anomalous Polarization of the Gamma Ophiuchi Debris Disk

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21537403w&link_type=abstract

American Astronomical Society, AAS Meeting #215, #374.03; Bulletin of the American Astronomical Society, Vol. 42, p.582

Astronomy and Astrophysics

Astronomy

Scientific paper

Using the POLISH instrument at the Lick 3-m, we have detected significant intrinsic, disk-integrated, optical polarization of the gamma Oph debris disk as P = (1.052 +/- 0.068) x 10-4. This value is corrected for interstellar polarization, which is estimated from the nearby star beta Oph. The literature reports a disk optical depth of tau = 0.6 x 10-4, and the comparable degree of polarization indicates efficient optical scattering by the dust grains in the inner region of the disk. The disk-integrated polarization PA is 50.4 +/- 1.4 degrees, which is aligned with high significance to the disk major axis measured in Spitzer 70 micron images (Su et al. 2008). However, such a high degree of polarization is expected to be aligned with the disk minor axis from simple, single scattering. The nearly 90 degree rotation between the expected and true polarization indicates structural differences between the optically-scattering inner disk and the thermally-emitting outer disk. In contrast, the disk-integrated polarization of the massive, tau = 84 x 10-4 debris disk HD 141569 is observed to be P = (55.59 +/- 0.82) x 10-4 and lies at a PA of 87.77 +/- 0.74 degrees. This polarization is aligned with high significance to the disk minor axis from Hubble V-band imaging (Clampin et al. 2003) as expected from simple, single scattering. We find excellent agreement in polarization PA, for many strongly polarized standard stars, between our observations and the catalog of Heiles (2000). This indicates that the anomalous polarization of the gamma Oph debris disk is a real phenomenon and not due to instrumental systematic effects. Our lack of optical detection of the gamma Oph disk with Hubble shows that observations of aperture-integrated polarization with high-precision polarimeters can be an efficient way to identify debris disks and guide deep imaging campaigns.

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