Coronagraphic Polarimetry of HST-Resolved Circumstellar T Tauri and Debris Disks

1
Coronagraphic Polarimetry of HST-Resolved
Circumstellar T Tauri and Debris Disks
Glenn Schneider (The University of Arizona, Dean
C. Hines (Space Science Institute)and the HST/GO
108521 108472 Teams
Abstract The formation of planetary systems is
intimately linked to the dust population in
circumstellar disks, thus understanding dust
grain evolution is essential to advancing our
understanding of how planets form. While it is
well established that stars form in ISM-like
protostellar environments, the connection to now
observable light-scattering circumstellar disks
and the processes of planet formation is still
very uncertain. Mid-IR spectral studies suggest
that disk grains are growing in the environments
of young stellar objects during the putative
planet-formation epoch. Structures revealed in
well resolved images of older circumstellar
debris disks suggest gravitational influences on
the disks from putative co-orbital bodies of
planetary mass. To further elucidate the dust and
systemic properties in potentially planet-forming
systems, we have undertaken two symbiotic HST
imaging programs that exploit the recently
commissioned capabilities of coronagraphic
polarimetry with the Near Infrared Camera and
Multi-Object Spectrometer (NICMOS), probing dust
structures in T Tauri circumstellar disks during
the early epochs of planet formation, and debris
disks around older stars. We present the first
observational results from these two programs in
light of earlier commission observations of TW
Hya, focusing on the scattered light disks around
the T Tauri star GM Aur and the debris disk
associated with HR 32297, along with optical
(ACS) coronagraphic polarimetry of the unusual
dust structure around HD 61005. Support for this
work was provided by NASA through grant numbers
GO-9768. 10847 and 10852 from the Space Telescope
Science Institute, which is operated by
Association of Universities for Research in
Astronomy Incorporated, under NASA contract
NAS5-26555NASA.
Optically Thin Debris Disk Scattering
Optically Thick T-Tauri Disk Scattering
Figure 2 HST/NICMOS coronagraphic polarimetry of
the debris disk associated with HD 32297,
originally imaged with NICMOS in total light by
Schneider, Silverstone Hines 2005, ApJ, 629,
L117. Polarizations 20 are measured along the
mid-plane of this nearly edge-on disk.
Figure 1 Coronagraphic polarimetry of GM Aur
comparing polarimetry results without (top) and
with (bottom) matched PSF-subtraction. Without
subtraction of an unpolarized PSF-star, the
polarization fraction of the GM Aur disk is
diluted by residual instrumentally diffracted
and scattered light from the coronagraphicaly
occulted (unpolarized) central star. The efficacy
of the technique is born out by the essentially
identical position angle and polarized intensity
images in the right two columns. PSF subtraction
enables decoupling the polarization fraction and
total intensity (2 mm flux density) with
accurate measurements of both (overcoming one of
the primary difficulties encountered in
ground-based AO polarimetry). These observations
are from GO 10852 (PI Schneider).
Figure 3 Optical coronagraphic imaging
polarimetry of the debris disk associated 100
Myr old star HD 61005, which is a G9V star at D
34.6 pc. These optical images were obtained with
the Advanced Camera for Surveys (ACS) aboard HST.
This extraordinary system was fisrt imaged in
total light with NICMOS (Hines et al. 2007, ApJ,
671, L165). The swept morphology appears to be
caused by a collision between the debris system
and an enhanced density cloud within the
interstellar medium. The polarized intensity
image reveals a ridge of highly polarized (30)
light along the putative leading egde of the
disk.
1Glenn Schneider (PI University of Arizona),
Dean C. Hines (Space Science Institute), Angela
S. Cotera (SETI Institute), Francois Menard
(Universite de Grenoble), Christophe Pinte
(Universite de Grenoble), Karl Stapelfeldt
(JPL), Barbara A. Whitney (Space Science
Institute)
2Dean C. Hines (PI Space Science Institute),
Glenn Schneider (University of Arizona),
Jean-Charles Augereau (Universite de Grenoble,
Dana E. Backman (NASA Ames), Angela S. Cotera
(SETI Institute), James R. Graham (UC Berkeley),
Paul Kalas (UC Berkeley), Francois Menard
(Universite de Grenoble), Stanimir A.
Metchev (UCLA), Deborah Padgett (SSC), Dan E.
Potter (University of Arizona), Christophe Pinte
(Universite de Grenoble), Murray
Silverstone (Eureka), Karl Stapelfeldt (JPL),
Barbara A. Whitney (Space Science Institute)