Letter to the Editor

VLTNACO and SubaruCIAO JHK-band high-resolution imaging polarimetry of the Herbig Be star R Monocerotis

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

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 JK_S-band images of ~01 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 in the J, H, and K bands. In this region, the polarization values are as low as %, %, and %, 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 (%, %, and %).

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.