Article

Resolving and Probing the Circumstellar Disk of the Herbig Ae Star MWC 480 at λ = 1.4 mm: Evolved Dust?

University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
The Astrophysical Journal (Impact Factor: 6.28). 11/2006; 651(1):321-327. DOI: 10.1086/507693
Source: arXiv

ABSTRACT We present high-resolution 0.45"×0.32" observations from the BIMA array toward the Herbig Ae system MWC 480 in the lambda=1.4 mm dust continuum. We resolve a circumstellar disk of radius ~170 AU and constrain the disk parameters by comparing the observations to flat-disk models. These results show that the typical fit parameters of the disk, such as the mass, MD~0.04-0.18 Msolar, and the surface density power-law index, p=0.5 or 1, are comparable to those of the lower mass T Tauri stars. The dust in the MWC 480 disk can be modeled as processed dust material (beta~0.8), similar to the Herbig Ae star CQ Tau disk; the fitted disk parameters are also consistent with less evolved dust (beta~1.2). The possibility of grain growth in the MWC 480 circumstellar disk is supported by the acceptable fits with beta~0.8. The surface density power-law profiles of p=0.5 and p=1 can be easily fitted to the MWC 480 disk; however, a surface density power-law profile similar to the minimum mass solar nebula model p=1.5 is ruled out at an 80% confidence level.

0 Followers
 · 
73 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a high spatial resolution submillimeter continuum survey of 24 circumstellar disks in the Tau-Aur and Oph-Sco star formation regions using the SMA. In the context of a simple model, we use broadband SEDs and submillimeter visibilities to derive constraints on some basic parameters that describe the structure of these disks. For the typical disk in the sample we infer a radial surface density distribution \Sigma ~ r^-p with a median p ~ 0.5, although consideration of the systematic effects of some of our assumptions suggest that steeper distributions with p ~ 0.7-1.0 are more reasonable. The distribution of the outer radii of these disks shows a distinct peak at R_d = 200 AU, with only a few cases where the disk emission is completely unresolved. Based on these disk structure measurements, the mass accretion rates, and the typical spectral and spatial distributions of submillimeter emission, we show that the observations are in good agreement with similarity solutions for steady accretion disks that have a viscosity parameter alpha ~ 0.01. We provide new estimates of the spectral dependence of the disk opacity with a median spectral index of ~0.7, corrected for optically thick emission. This typical value is consistent with model predictions for the collisional growth of solids to millimeter size scales in the outer disk. Although direct constraints on planet formation in these disks are not currently available, the extrapolated density distributions inferred here are substantially shallower than those calculated based on the solar system or extrasolar planets and typically used in planet formation models. It is possible that we are substantially underestimating disk densities due to an incomplete submillimeter opacity prescription.
    The Astrophysical Journal 10/2006; 659(1). DOI:10.1086/511741 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present results from SMA observations of the star forming region Cepheus A-East at ~340 GHz (875 micron) with 0.7'' - 2'' resolution. At least four compact submm continuum sources have been detected, as well as a rich forest of hot core line emission. Two kinematically, chemically, and thermally distinct regions of molecular emission are present in the vicinity of the HW2 thermal jet, both spatially distinct from the submm counterpart to HW2. We propose that this emission is indicative of multiple protostars rather than a massive disk as reported by Patel et al. (2005). Comment: 4 pages, Figures 1 and 3 are in color, latex uses emulateapj.sty. Accepted to ApJ Letters. Figures 1 and 3 have been degraded; higher quality figures available at http://www.cv.nrao.edu/~cbrogan/CepA/
    The Astrophysical Journal 03/2007; 660(2). DOI:10.1086/518390 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the apparent discrepancy between gas and dust outer radii derived from millimeter observations of protoplanetary disks. Using 230 and 345 GHz continuum and CO J=3-2 data from the Submillimeter Array for four nearby disk systems (HD 163296, TW Hydrae, GM Aurigae, and MWC 480), we examine models of circumstellar disk structure and the effects of their treatment of the outer disk edge. We show that for these disks, models described by power laws in surface density and temperature that are truncated at an outer radius are incapable of reproducing both the gas and dust emission simultaneously: the outer radius derived from the dust continuum emission is always significantly smaller than the extent of the molecular gas disk traced by CO emission. However, a simple model motivated by similarity solutions of the time evolution of accretion disks that includes a tapered exponential edge in the surface density distribution (and the same number of free parameters) does much better at reproducing both the gas and dust emission. While this analysis does not rule out the disparate radii implied by the truncated power-law models, a realistic alternative disk model, grounded in the physics of accretion, provides a consistent picture for the extent of both the gas and dust. Comment: 9 pages, 2 figures, accepted for publication in ApJ
    The Astrophysical Journal 01/2008; 678(2). DOI:10.1086/586730 · 6.28 Impact Factor
Show more

Preview

Download
0 Downloads
Available from