HK-band imaging polarimetry and radiative transfer modeling of the massive young stellar object CRL 2136

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: murakawa@mpifr-bonn.mpg.de

Received: 3 April 2008
Accepted: 6 August 2007

Abstract

Aims. We investigate the physical properties of the dust environment of the massive proto-stellar object CRL 2136 by means of two-dimensional radiative transfer modeling, which combines fitting of the spectral energy distribution, the intensity images, and the polarization images.

Methods. We obtained polarimetric images of CRL 2136 in the H and K bands using the CIAO instrument on the 8 m Subaru telescope. We developed a new Monte Carlo code which can deal with multiple-grain models and computes the SED, the dust temperature, and the Stokes IQUV images. With this code, we performed two-dimensional modeling of CRL 2136's circumstellar disk and envelope.

Results. Our images show a compact infrared source, two bright lobes extending towards the south and east, and two faint lobes extending towards the northwest and west. The polarization images show a polarization disk near the central star with a position angle of ~ -135°, a polarization vector alignment approximately parallel to the polarization disk, and a region with low polarization between the eastern and the southern lobes. In our modeling, we assume three grain models: bare grains, warm grains with a crystalline water ice mantle, and cold grains with an amorphous water ice mantle. We obtained a maximum grain core size of 0.45 μm. We found that the CRL 2136 disk has a low disk mass of 0.007 , a large radius of 2000 AU, a scale height of 1.0, and a low accretion rate of 2.1 10^-7  yr^-1 compared to an envelope mass infall rate of 1.0 10^-4  yr^-1.

Conclusions. The predicted environment of the disk and the envelope is consistent with a scenario in which the central star forms rapidly (~ 2 10⁵ yr), with a high mass infalling rate, and nearly isotropically (large disk scale height) in the early phase. Then, the accretion of the disk matter is prevented by the strong radiation pressure from the luminous central star, resulting in a low disk mass and a low accretion rate.