Resolving and Probing the Circumstellar Disk of the Herbig Ae Star MWC 480 at lambda = 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.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a substantial extension of the mm-wave continuum photometry catalog for Taurus circumstellar dust disks. Combining new Submillimeter Array data with measurements in the literature, we construct a mm-wave luminosity distribution for Class II disks that is statistically complete for stellar hosts with spectral types earlier than M8.5 and has a (3-sigma) depth of ~3 mJy. The resulting census eliminates a longstanding bias against disks with late-type hosts, and thereby reveals a strong correlation between L_mm and the host spectral type. We confirm that this corresponds to a statistically robust relationship between the masses of dust disks and the stars that host them. A Bayesian regression technique is used to characterize these relationships: the results indicate a typical 1.3 mm flux density of 25 mJy for solar mass hosts and a power-law scaling L_mm \propto M_star^1.5-2.0. We suggest that a reasonable treatment of dust temperature in the conversion from L_mm to M_disk favors an inherently linear M_disk \propto M_star scaling, with a typical disk-to-star mass ratio of $\sim$0.2--0.6%. The RMS dispersion around this regression is 0.7 dex, suggesting that the combined effects of diverse evolutionary states, dust opacities, and temperatures in these disks imprint a FWHM range of a factor of 40 on the inferred M_disk (or L_mm) at any given host mass. We argue that this relationship between M_disk and M_star likely represents the origin of the inferred correlation between giant planet frequency and host star mass in the exoplanet population, and provides some basic support for the core accretion model for planet formation. Moreover, we caution that selection bias must be considered in comparative studies of disk evolution, and illustrate that fact with statistical comparisons of L_mm between Taurus and other clusters (abridged).
    The Astrophysical Journal 05/2013; 771(2). DOI:10.1088/0004-637X/771/2/129 · 6.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: With a combination of adaptive optics imaging and a multi-epoch common proper motion search, we have conducted a large volume-limited (D $\le$ 75 pc) multiplicity survey of A-type stars, sensitive to companions beyond 30 au. The sample for the Volume-limited A-STar (VAST) survey consists of 435 A-type stars: 363 stars were observed with adaptive optics, 228 stars were searched for wide common proper motion companions and 156 stars were measured with both techniques. The projected separation coverage of the VAST survey extends from 30 to 45,000 au. A total of 137 stellar companions were resolved, including 64 new detections from the VAST survey, and the companion star fraction, projected separation distribution and mass ratio distribution were measured. The separation distribution forms a log-normal distribution similar to the solar-type binary distribution, but with a peak shifted to a significantly wider value of 387 (+132,-98) au. Integrating the fit to the distribution over the 30 to 10,000 au observed range, the companion star fraction for A-type stars is estimated as 33.8%+-2.6%. The mass ratio distribution of closer (<125 au) binaries is distinct from that of wider systems, with a flat distribution for close systems and a distribution that tends towards smaller mass ratios for wider binaries. Combining this result with previous spectroscopic surveys of A-type stars gives an estimate of the total companion star fraction of 68.9%+-7.0%. The most complete assessment of higher order multiples was estimated from the 156-star subset of the VAST sample with both adaptive optics and common proper motion measurements, combined with a literature search for companions, yielding a lower limit on the frequency of single, binary, triple, quadruple and quintuple A-type star systems of 56.4 (-4.0,+3.8), 32.1 (-3.5,+3.9), 9.0 (-1.8,+2.8), 1.9 (-0.6,+1.8) and 0.6 (-0.2,+1.4) per cent, respectively.
    Monthly Notices of the Royal Astronomical Society 11/2013; 437(2). DOI:10.1093/mnras/stt1932 · 5.23 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Millimeter-wavelength polarization measurements offer a promising method for probing the geometry of magnetic fields in circumstellar disks. Single dish observations and theoretical work have hinted that magnetic field geometries might be predominantly toroidal, and that disks should exhibit millimeter polarization fractions of 2-3%. While subsequent work has not confirmed these high polarization fractions, either the wavelength of observation or the target sources differed from the original observations. Here we present new polarimetric observations of three nearby circumstellar disks at 2" resolution with the Submillimeter Array (SMA) and the Combined Array for Research in Millimeter Astronomy (CARMA). We reobserve GM Aur and DG Tau, the systems in which millimeter polarization detections have been claimed. Despite higher resolution and sensitivity at wavelengths similar to the previous observations, the new observations do not show significant polarization. We also add observations of a new HAeBe system, MWC 480. These observations demonstrate that a very low (<0.5%) polarization fraction is probably common at large (>100 AU) scales in bright circumstellar disks. We suggest that high-resolution observations may be worthwhile to probe magnetic field structure on linear distances smaller than the disk scale height, as well as in regions closer to the star that may have larger MRI-induced magnetic field strengths.
    The Astronomical Journal 02/2013; 145(4). DOI:10.1088/0004-6256/145/4/115 · 4.97 Impact Factor


Available from