Two-dimensional Radiative Transfer in Protostellar Envelopes. I. Effects of Geometry on Class I Sources

By B. Whitney, K. Wood, J. Bjorkman, Michael J. Wolff. 2003

394 citations recorded by the source corpus.

We present two-dimensional radiation transfer models of class I protostars and show the effect of including more realistic geometries on the resulting spectral energy distributions and images. We begin with a rotationally flattened infalling envelope as our comparison model and add a flared disk and bipolar cavity. The disk affects the spectral energy distribution most strongly at edge-on inclinations, causing a broad dip at about 10 μm (independent of the silicate feature) due to high extinction and low scattering albedo in this wavelength region. The bipolar cavities allow more direct stellar+disk radiation to emerge into polar directions and more scattering radiation to emerge into all directions. The wavelength-integrated flux, often interpreted as luminosity, varies with viewing angle, with pole-on viewing angles seeing 2-4 times as much flux as edge-on, depending on geometry. Thus, observational estimates of luminosity should take into account the inclination of a source. The envelopes with cavities are significantly bluer in near-IR and mid-IR color-color plots than those without cavities. Using one-dimensional models to interpret Class I sources with bipolar cavities would lead to an underestimate of envelope mass and an overestimate of the implied evolutionary state. We compute images at near-, mid-, and far-IR wavelengths. We find that the mid-IR colors and images are sensitive to scattering albedo and that the flared disk shadows the midplane on large size scales at all wavelengths plotted. Finally, our models produce polarization spectra that can be used to diagnose dust properties, such as albedo variations due to grain growth. Our results of polarization across the 3.1 μm ice feature agree well with observations for ice mantles covering 5% of the radius of the grains.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/a2bff017ec20afad7200b77273ed24290996e1d6

How researchers see this paper

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In Astronomy and Astrophysics

1. N. Evans II
2. P. Myers
3. E. Dishoeck
4. Mark R. Krumholz
5. L. Hartmann
6. C. Dullemond
7. B. Whitney
8. L. Allen

In Atmospheric Science

1. E. Dishoeck
2. B. Whitney
3. N. Evans II
4. K. Oberg
5. C. Dullemond
6. A. Tielens
7. Zhaohuan Zhu
8. R. Dong

In Spectroscopy

1. N. Evans II
2. E. Dishoeck
3. P. Myers
4. C. Dullemond
5. K. Oberg
6. L. Hartmann
7. L. Allen
8. A. Tielens

Citations in the corpus

• YOUNG STELLAR OBJECTS IN THE GOULD BELT (2015, background): “…a distinct physical stage, and in reality the correlation between observational SED Class and 13 physical Stage is weakened by the effects of geometry, extinction, and accretion history (e.g., Whitney et al. 2003; Young & Evans 2005; Robitaille et al. 2006; Crapsi et al. 2008; Dunham et al. 2010).”
• The c2d Spitzer Spectroscopic Survey of Ices around Low-Mass Young Stellar Objects. I. H2O and the 5-8 μm Bands (2007, background): “The continuum SED underlying the many blended absorption features originates from warm dust near the central star and is dependent on poorly characterized parameters such as disk and envelope mass, size, and inclination, and dust composition (Whitney et al. 2003).”
• Identifying the Low-Luminosity Population of Embedded Protostars in the c2d Observations of Clouds and Cores (2007, methodology): “D models of sources (e.g., Whitney et al. 2003a; Whitney et al. 2003b; Robitaille et al. 2006) shows that, even at the most extreme pole-on inclinations, the effects of outflow cavities are unlikely to result in an observed SED more luminous in the near-infrared than at 24 and 70 µm.”
• Observational Signatures of Planets in Protoplanetary Disks I: Gaps Opened by Single and Multiple Young Planets in Disks (2014, methodology): “Monte Carlo Radiative Transfer Simulations We carry out 3D MCRT simulations using the code developed by Whitney et al. (2013, see also Whitney et al. 2003a,b).”
• SPITZER SAGE SURVEY OF THE LARGE MAGELLANIC CLOUD. III. STAR FORMATION AND ∼1000 NEW CANDIDATE YOUNG STELLAR OBJECTS (2008, methodology): “The models accurately compute scattered and thermal emission from dust in a physically plausible geometry, which consists of a stellar source that illuminates a dusty disk, envelope, and bipolar cavity (Whitney et al. 2003a, 2003b).”
• The evolution of the spectral energy distribution in massive young stellar objects (2008, methodology): “Mass, temperature and β are the three free parameters in our greybody fits and provide a decent representation of the global properties of the FIR-mm clumps not associated with mid-IR emission and which cannot be fitted by the Whitney et al. (2003) models.”
• Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A Grid of 200,000 YSO Model SEDs (2006, methodology): “The main effect of varying the aperture is a bluing of the colors of Stage I sources with larger aperture, as discussed in Whitney et al. (2003b).”
• STAR FORMATION IN THE CENTRAL 400 PC OF THE MILKY WAY: EVIDENCE FOR A POPULATION OF MASSIVE YOUNG STELLAR OBJECTS (2009, methodology): “YSOs are also known to have excess emission in infrared wavelengths and are characterized by dusty envelopes and disks that absorb the radiation from the central protostar (Whitney et al. 2003a; Adams et al. 1987).”
• On the formation of Hα line emission around classical T Tauri stars (2006, methodology): “The index of the mid-plane temperature power law is adopted from the dust radiative transfer model of Whitney et al. (2003) who found the innermost part of the accretion disc has q = −1.15.”
• A Perspective from Extinct Radionuclides on a Young Stellar Object: The Sun and Its Accretion Disk (2011, background): “This corresponds to the transition between class I and class II YSOs (examples of midplane temperature profiles in class I and II sources can be found in D’Alessio et al. 2005 and Whitney et al. 2003).”
• HIGH- AND INTERMEDIATE-MASS YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD (2009, methodology): “The SAGE YSOs are initially identified using a complex set of color and magnitude criteria based on the predictions from a grid of radiative transfer models that attempt to simulate the emission from YSOs (Whitney et al. 2003a, 2003b; Robitaille et al. 2006).”
• EVOLUTIONARY SIGNATURES IN THE FORMATION OF LOW-MASS PROTOSTARS. II. TOWARD RECONCILING MODELS AND OBSERVATIONS (2005, methodology): “D models of embedded protostars that include disks (e.g., Whitney et al. 2003a; Whitney et al. 2003b; Robitaille et al. 2006; Crapsi et al. 2008).”
• The chemical history of molecules in circumstellar disks - I. Ices (2009, background): “As in Whitney et al. (2003), the outflow has some effect on the temperature profile.”
• The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. III. Perseus Observed with IRAC (2006, background): “Whitney et al. (2003) for example showed that the presence of outflow cavities likewise would lead to bluer colors - although this effect should be important for both [5.8]-[8.0] and [3.6]-[4.5] colors according to the models of Whitney et al. (2003).”
• The Formation of Massive Stars: Accretion, Disks, and the Development of Hypercompact H II Regions (2006, methodology): “A limitation of the model is that the midplane density is not defined, whereas a more complete modelwould describe the density across themidplane as a pressuresupported disk (Shakura & Sunyaev 1973; Lynden-Bell & Pringle 1974; Pringle 1981; Hartmann 1998; Whitney et al. 2003).”
• THE HERSCHEL ORION PROTOSTAR SURVEY: SPECTRAL ENERGY DISTRIBUTIONS AND FITS USING A GRID OF PROTOSTELLAR MODELS (2016, background): “It influences the near- to farIR slope, the depth of the silicate feature, the emission peak, and the fraction of light emitted at the longest wavelengths (see, e.g., Whitney et al. 2003a).”