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

Murakawa, K.; Preibisch, Thomas; Kraus, Stefan; Weigelt, G.

doi:10.1051/0004-6361:200809901

Cited by 19 publications

(35 citation statements)

References 85 publications

(113 reference statements)

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“…These results on the disk masses are in accordance with other studies of MYSOs (e.g. Murakawa et al 2008) and also with some evolved early-type Herbig Be stars (Alonso-Albi et al 2009). Were the disk outer radius much smaller than the assumed 500 AU and similar to the small outer radii found for the Herbig Be stars, then the disk mass should be scaled down accordingly: a 50 AU outer radius results in a disk mass of 5 × 10 −4 M .…”

Section: The Contribution Of An Accretion Disksupporting

confidence: 92%

The origin of mid-infrared emission in massive young stellar objects: multi-baseline VLTI observations of W33A

Wit

Hoare

Oudmaijer

et al. 2010

A&A

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Aims. In this paper we aim to determine the structure on 100 AU scales of the massive young stellar object W33A, using interferometric observations in the mid-infrared. This emission could be caused by a variety of elements, for example, the inner protostellar envelope, outflow cavity walls, or a dusty or gaseous accretion disk. Methods. We used the Unit Telescopes of the VLT Interferometer in conjunction with the MIDI instrument to obtain spectrally dispersed visibilities in the N-band on 4 baselines with an angular resolution between 25 and 60 milli-arcsec (equivalent to 95 and 228 AU at 3.8 kpc). The visibility spectra and spectral energy distribution were compared to 2D-axi-symmetric dust radiative transfer models with a geometry that includes a rotationally flattened envelope and outflow cavities. We assumed an O 7.5 ZAMS star as the central source, consistent with the observed bolometric luminosity. The observations were compared to models with and without (dusty and gaseous) accretion disks. Results. The visibilities are between 5% and 15%, and the non-spherically symmetric emitting structure has a typical size of 100 AU. A satisfactory model is constructed to reproduce the visibility spectra for each (u, v) point. It fits the N-band flux spectrum, the midinfrared slope, the far-infrared peak, and the (sub)mm regime of the SED. It produces a 350 μm morphology consistent with the observations. Conclusions. The mid-infrared emission of W33A on 100 AU scales is dominated by the irradiated walls of the cavity sculpted by the outflow. The protostellar envelope has an equivalent mass infall rate of 7.5 × 10 −4 M yr −1 , and an outflow opening angle of 2θ = 20 • . The visibilities rule out the presence of any dust disk with total (gas and dust) mass more than 0.01 M . Within the model, this implies a diskṀ acc of less than 1.1 × 10 −7 (α/0.01) M yr −1 , where α is the viscosity of the Shakura-Sunyaev prescription. However, optically thick accretion disks, which are inside the dust sublimation radius, are allowed to accrete at rates equalling the envelope's mass infall rate (up to 10 −3 M yr −1 ) without substantially affecting the visibilities due to the extinction by the extremely massive envelope of W33A.

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Section: The Contribution Of An Accretion Disksupporting

confidence: 92%

The origin of mid-infrared emission in massive young stellar objects: multi-baseline VLTI observations of W33A

Wit

Hoare

Oudmaijer

et al. 2010

A&A

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“…With the aforementioned assumptions, we produced polarization images of the 30 parameter sets in the optical and NIR using our own Monte Carlo STSH code (Murakawa et al 2008b). This code can treat multiple dust models for different regions in the model geometry and can compute the SED, the dust temperature, and the Stokes IQUV images.…”

Section: Effects Of the Disk Height And The Grain Sizementioning

confidence: 99%

“…On the other hand, some massive stars have high NIR polarizations; e.g. G333.6 -0.2; Fujiyoshi et al (2001), S87;Chen et al (2004), AFGL 437; Meakin et al (2005), CRL 2136; Murakawa et al (2008b), S255 IRS1; Simpson et al (2009). The common feature is that the central star features are seen through the disk, and the polarization vectors are aligned along the disk plane.…”

Section: Generalized Scattering Modelmentioning

confidence: 99%

Polarization disks in near-infrared high-resolution imaging

Murakawa

2010

A&A

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A polarization disk is a characteristic feature of optical and near-infrared (NIR) polarimetric images of young stellar objects (YSOs) and is regarded as convincing evidence that a dust disk is present. We analyze high-resolution linear polarization maps of a sample of low-mass YSO disk models by means of radiative transfer calculations to investigate the effects of the disk geometry and grain sizes on polarization properties. Our modeling assumes spherical grains with a power-law size distribution of n (a) ∝ a −3.5 ; 0.005 μm ≤ a ≤ a max and with a fixed a max of 0.25 μm for the outer envelope and a different a max for the disk. The parameters to examine are the disk height (i.e. the ratio of the disk height to the outer disk radius H of 0.1 to 1.0) and the dust sizes in the disk (i.e. a max of 0.25 to 1000.0 μm). In a near pole-on view, the polarization vectors are centro-symmetrically aligned even towards the disk, but the degree of polarization can be different from the envelope. We predict that the pole-on disk can be distinguished from the envelope. In contrast, the model images show a bipolar nebulosity and a polarization disk with a vector alignment in edge-on view. The polarization is low (<10%) for large grains or low H values and high (up to ∼80%) for small grains and high H values. In contrast, comparably constant polarizations (20-40%) are obtained in the optical. The wavelength dependence in low NIR polarization cases is often detected in many T Tauri stars, suggesting that grain growth or an advanced disk accretion is expected in these objects. The opposite trend in high NIR polarization cases, which is found in some low-mass protostars, is reproduced with spherical grain models. To understand our results, we developed a generalized scattering model, which is an extension of the vector alignment mechanism. In the lowmass star disk case, multiple-scattered light behaves as if it chooses paths of comparably low optical density region (e.g. the disk surface), avoiding a high density, equatorial region, which we call the roundabout effect. The single-scattered light does not reach the observer, and the double-scattered light contributes the most flux. However, the effect of the first scattering still appears in the final polarization status. The higher the disk height in our models, the closer to 90 • the scattering angle on the disk surface, resulting in a higher polarization. The variety of the wavelength dependence on the polarization is also an example of the roundabout effect. In the optical, only stray light passed through the envelope reaches the observer. Thus, the optical polarization is characterized by scattering by small grains in the envelope. On the other hand, since the NIR photons can pass through a somewhat inner part of the disk, the NIR polarization can still offer information on the dust and geometry of the disk. We expect that a polarization disk analysis in high-resolution data, such as the one we present, offers opportunities to investigate the grain growth and dust se...

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“…To perform radiative transfer calculations, we used our own Monte Carlo STSH code, which can compute the SED, the dust temperature, and the Stokes IQUV images of models with arbitrary geometries (up to three-dimension) and multiple dust models (Murakawa et al 2008b). We first tried some parameter sets to find approximate solutions and appropriate parameter grids and ranges to scan.…”

Section: Resultsmentioning

confidence: 99%

“…The F1 form is most widely used for YSO disk models; however, this form does not guarantee a better fit to all observations, and an alternative form of F2 is also exceptionally considered (e.g. Lazareff et al 1990;Fischer et al 1996;Murakawa et al 2008b). In this form, the values of α and β are free parameters.…”

Section: Radiative Transfer Modelingmentioning

confidence: 99%

Radiative transfer modeling of the dust disk of the Herbig Be star R Monocerotis

Murakawa

2010

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Our previous near-infrared (NIR), high-resolution polarimetric images of the Herbig Be star R Mon show that the polarization disk has a large, nearly constant angular size of ∼4 in the JHK bands, low polarizations of 1.1-1.5% in the H and K bands, and somewhat centro-symmetrical vector alignment. To derive the disk geometry parameters and grain sizes that explain this result, we modeled R Mon's dust disk by combining it with previously obtained spectral energy distribution and gas phase observations. Our model assumes an inner disk and outer envelope structure, dust of different populations for the disk and envelope, and a power-law size distribution of n (a) ∝ a −3.5 with 0.005 μm ≤ a ≤ a max μm. We obtained an outer disk radius of 3000 AU, a ratio of the height to the radius of the disk of H 0 = 0.4, a V-band optical depth of 4.2 in the disk midplane, and an a max of 1000.0 μm for the disk. Such a large extension of the disk is similar to the ones of the central feature detected in previous observations in the CO emission lines (1500 AU) and the 2.7 mm continuum (3000 AU). The shape and angular size of the polarization disk in our model fit the observations and approximately trace the projected appearance of the real disk. Since the estimated dust disk height has an intermediate value and is lower than the gas phase (CO) disk height (H 0 = 1.0), it is likely that the dust settling is ongoing. Our selected model with a large dust size with an a max of 1000.0 μm in the inner part of the disk and a disk mass of 0.02 M fit the near-infrared polarization towards the disk and the mid-infrared to millimeter fluxes well. Our estimated disk mass roughly agrees with a previous gas phase modeling of ∼0.01 M . Such a large grain model reproduces low NIR polarizations (1.6%), which is consistent with our observation. Not detecting the vector alignment is explained with this large grain model and an intermediate optical depth of the disk. We expect that R Mon's disk contrasts to the typical T Tauri and Herbig Ae disks in terms of an expected large outer disk radius and an intermediate optical depth. Evidence of the dust settling and large grains suggests that the dust in R Mon's disk grows faster than the disk accretion advances, which is theoretically predicted in typical T Tauri disks.

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

Cited by 19 publications

References 85 publications

The origin of mid-infrared emission in massive young stellar objects: multi-baseline VLTI observations of W33A

The origin of mid-infrared emission in massive young stellar objects: multi-baseline VLTI observations of W33A

Polarization disks in near-infrared high-resolution imaging

Radiative transfer modeling of the dust disk of the Herbig Be star R Monocerotis

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