Constraining the Evolutionary Stage of Class I Protostars: Multiwavelength Observations and Modeling

Abstract

We present new Keck images at 0.9 m and OVRO 1.3 mm continuum images of five Class I protostars in the Taurus star-forming region. We analyze these data in conjunction with broadband spectral energy distributions (SEDs) and 8-13 m spectra from the literature using a Monte Carlo radiative transfer code. By fitting models for the circumstellar dust distributions simultaneously to the scattered light images, millimeter continuum data, and the SEDs, we attempt to distinguish between flared disks, infalling envelopes with outflow cavities, and combinations of disks and envelopes. For each of these circumstellar density distributions, we generate grids of models for varying geometries, dust masses, and accretion rates and determine the best fits by minimizing the residuals between model and data. Comparison of the residuals for best-fit disk, envelope, and disk+envelope models demonstrates that, in general, models incorporating both massive envelopes and massive embedded disks fit the imaging+SED data best. The implied envelope infall rates for these disk+envelope models are generally consistent with infall rates derived by previous investigators, although they are approximately an order of magnitude larger than inner disk accretion rates inferred from recent spectroscopic measurements. In addition, the disk masses inferred from our models are close to or larger than the limit for gravitationally stable disks, indicating that Class I disks may undergo periodic episodes of enhanced accretion, perhaps as a result of gravitational instabilities. An important caveat to these results is that in some cases, no single model can fit all of the imaging and SED data well, suggesting that further refinements to models of the circumstellar dust distributions around Class I sources are necessary. We discuss several potential improvements to the models, as well as new constraints that will become available with upcoming millimeter and infrared facilities.

Disk Masses for Embedded Class I Protostars in the Taurus Molecular Cloud

“…This system has been modeled previously and found to have a compact disk, with a disk radius of 30-100 au and moderate (20°-60°) inclinations (Kenyon et al 1993;Whitney et al 1997;Eisner et al 2005;Furlan et al 2008). Our best-fit model is in Table 2 Best-fit Model Parameters ), who find a disk radius of 30 au, an envelope radius of 500 au, and an inclination of 24°.…”

“…The model includes a central star, protoplanetary disk, and a rotating collapsing envelope, following the modeling scheme of Eisner et al (2005), Eisner (2012), and Sheehan & Eisner (2014). These previous studies ran large grids of radiative transfer models and fit those grids to multiwavelength data sets to determine system parameters.…”

“…The best way, however, to probe the underlying density distribution is through spatially resolved observations of optically thin matter. Detailed radiative transfer modeling of data sets at multiple wavelengths can be used to break model degeneracies, constrain parameters like temperature and opacity, and determine physical properties of the system (e.g., Osorio et al 2003;Wolf et al 2003;Eisner et al 2005;Lommen et al 2008;Gramajo et al 2010;Eisner 2012;Sheehan & Eisner 2014.…”

The circumstellar disc in the Bok globule CB 26

“…We thus implement a model for a rotating envelope resulting from infalling matter similar to Whitney et al (2003); Eisner et al (2005):…”

Embedded Protostellar Disks Around (Sub-)Solar Protostars. I. Disk Structure and Evolution

“…The added complication of the envelope structure in the embedded systems makes an extraction of disk parameters from interferometer data extraordinarily difficult with modern facilities. No wonder that most observations of disk properties have been focused on T Tauri disks (e.g., Akeson et al 2002;Kitamura et al 2002;Vicente & Alves 2005;Piétu et al 2007;Andrews & Williams 2007;Andrews et al 2009;Isella et al 2009, and many others) and considerably fewer attempted studies of the embedded disks have been done so far (e.g., Andrews & Williams 2005;Eisner et al 2005;Jørgensen et al 2009). …”