EDP Sciences
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Volume 488, Number 3, September IV 2008
Page(s) L75 - L78
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200810462
Published online 08 August 2008

A&A 488, L75-L78 (2008)
DOI: 10.1051/0004-6361:200810462


VLT/NACO and Subaru/CIAO JHK-band high-resolution imaging polarimetry of the Herbig Be star R Monocerotis

K. Murakawa1, T. Preibisch1, S. Kraus1, N. Ageorges2, K.-H. Hofmann1, M. Ishii3, S. Oya3, A. Rosen1, D. Schertl1, and G. Weigelt1

1  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    e-mail: murakawa@mpifr-bonn.mpg.de
2  European Southern Observatory (ESO), Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
3  Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku place, Hilo, HI 96720, USA

Received 25 June 2008 / Accepted 30 July 2008

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 $JK_{\rm S}$-band images of ~0$\farcs$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 $4\arcsec$ in the J, H, and K bands. In this region, the polarization values are as low as $P_J\sim7$%, $P_H\sim2$%, and $P_K\sim1$%, 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 ( $P_J \sim24$%, $P_H \sim 33$%, and $P_K\sim53$%).
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 $\mu$m. 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.

Key words: stars: individual: R Monocerotis -- circumstellar matter -- stars: imaging -- ISM: reflection nebulae -- infrared: stars

© ESO 2008