VLT/NACO and Subaru/CIAO JHK-band high-resolution imaging polarimetry of the Herbig Be star R Monocerotis
K. Murakawa, T. Preibisch, S. Kraus, N. Ageorges, K.-H. Hofmann, M. Ishii, S. Oya, A. Rosen, D. Schertl, and G. Weigelt
Astronomy and Astrophysics, Volume 488, Issue 3, pp.L75-L78 (2008)
Abstract
Aims.
We investigate the dust properties of the disk and envelope of the Herbig
Be star R Mon by means of near-infrared multiwavelength imaging polarimetry.
Methods. We obtained JHK-band polarimetric images using the adaptive optics
instruments NACO on the VLT, and CIAO on the Subaru telescope.
Results. Our NACO JKS-band images of ~0."1 angular resolution resolve
clearly the R Mon binary system as well as twisted string-like features in
the fan-shaped lobe. The polarimetric images reveal a butterfly-shaped
polarization disk with an almost constant shape and an extension of 4" in the J, H, and
K bands. In this region, the polarization
values are as low as PJ~7%, PH~2%, and PK~1%, and the polarization vectors are not systematically aligned along the
equatorial plane. On the other hand, highly polarized scattered light is
detected in the fan-shaped lobe (PJ~24%, PH~33%, and PK~53%).
Conclusions: Our polarimetric data suggests the presence of multiple grain populations
in the R Mon nebula. From our one-dimensional single scattering modeling,
the maximum grain size in the nebula at large scale is estimated to be 0.23 μm. On the other hand, the aforementioned properties of the
polarization disk and a nearly spherical appearance of the nebulosity
close to the central star suggests the presence of large grains
(micron-size or larger) in the polarization disk.
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