Gas and Dust Emission at the Outer Edge of Protoplanetary Disks

By A. Hughes, D. Wilner, C. Qi, M. Hogerheijde. 2008

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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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/0ec3891bd514cd6a3c73e2f59493c480e5d4824a

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Citations in the corpus

Protoplanetary Disks and Their Evolution (2011, background): “More precisely, Hughes et al. (2008) determine Rc = 30 − 200AU for four disks by fitting the profile in equation 4 to the continuum data.”
Dust Evolution and the Formation of Planetesimals (2016, background): “From the investigation of a sample of resolved images of disks, rc shows a wide range from tens to several hundred AU (Hughes et al. 2008; Andrews et al. 2009, 2010).”
A SPATIALLY RESOLVED VERTICAL TEMPERATURE GRADIENT IN THE HD 163296 DISK (2013, methodology): “We report values of the disk inclination and P.A. that differ by 180◦ from previous analyses based on less sensitive data (Isella et al. 2007; Hughes et al. 2008; Qi et al. 2011).”
WEAK TURBULENCE IN THE HD 163296 PROTOPLANETARY DISK REVEALED BY ALMA CO OBSERVATIONS (2015, methodology): “This functional form has also been successful in fitting both the dust and the gas (Hughes et al. 2008) including the different apparent radii for the gas and dust disk, although recent evidence suggests that in some systems the dust disks are smaller than the gaseous component (Andrews et al.…”
Unveiling the gas-and-dust disk structure in HD 163296 using ALMA observations (2013, background): “The previous value of γ = 1, reported in the literature by Hughes et al. (2008) as the value that simultaneously fits the continuum and the CO(3–2) emission as observed with the SMA, was also considered as a reference for the fitting.”
A SPATIALLY RESOLVED INNER HOLE IN THE DISK AROUND GM AURIGAE (2009, background): “REFERENCES Alexander, R. D. & Armitage, P. J. 2007, MNRAS, 375, 500 Andrews, S. M. & Williams, J. P. 2005, ApJ, 631, 1134 —.”
THE TW Hya DISK AT 870 μm: COMPARISON OF CO AND DUST RADIAL STRUCTURES (2011, methodology): “…(Krist et al. 2000; Trilling et al. 2001; Weinberger et al. 2002; Apai et al. 2004; Roberge et al. 2005), millimeter/radio-wave continuum images (Wilner et al. 2000, 2003, 2005; Hughes et al. 2007), and resolved molecular line maps (Qi et al. 2004, 2006, 2008; Hughes et al. 2008, 2011).”
STRUCTURE AND EVOLUTION OF PRE-MAIN-SEQUENCE CIRCUMSTELLAR DISKS (2009, methodology): “…been demonstrated that the power law parameterization fails to explain the differences in the radial extensions of the dust and the gas emission that are observed in a number of intermediate mass pre-main sequence stars (Piétu et al. 2005; Isella et al. 2007; Hughes et al. 2008, hereafter H08).”
PROTOPLANETARY DISK STRUCTURES IN OPHIUCHUS (2009, background): “Hughes et al. (2008) demonstrated that this discrepancy may be an artifact of the sharp Σ cut-off, and advocated a more gradual density taper at large disk radii.”
EMPIRICAL CONSTRAINTS ON TURBULENCE IN PROTOPLANETARY ACCRETION DISKS (2010, background): “…well-studied using spatially-resolved observations at millimeter wavelengths, so that excellent models of the temperature and density structure of the gas and dust disks are already available (Calvet et al. 2002; Isella et al. 2007, 2009; Hughes et al. 2008; Qi et al. 2004, 2006, 2008).”
A PARAMETRIC MODELING APPROACH TO MEASURING THE GAS MASSES OF CIRCUMSTELLAR DISKS (2013, background): “This has its basis in the works of Hughes et al. (2008) and Andrews et al. (2009), who followed theoretical descriptions by Lynden-Bell & Pringle (1974) and Hartmann et al. (1998).”
Molecules with ALMA at Planet-forming Scales (MAPS). I. Program Overview and Highlights (2021, methodology): “GM Aur’s large dust cavity of ∼35 au in radius was first inferred from SED modeling (Marsh & Mahoney 1992; Calvet et al. 2005; Espaillat et al. 2010) and later directly imaged using millimeter observations (Hughes et al. 2008).”
THE MASS DEPENDENCE BETWEEN PROTOPLANETARY DISKS AND THEIR STELLAR HOSTS (2013, unknown): “– 36 – 2005, 2007b; Rodmann et al. 2006; Cabrit et al. 2006; Bouy et al. 2008; Hughes et al. 2008, 2009; Schaefer et al. 2009; Isella et al. 2009, 2010, 2012; Hamidouche 2010; Öberg et al. 2010; Ricci et al. 2010, 2012, 2013; Andrews et al. 2011; Phan-Bao et al. 2011; Sandell et al. 2011; Cieza et…”
PROTOPLANETARY DISK STRUCTURES IN OPHIUCHUS. II. EXTENSION TO FAINTER SOURCES (2010, background): “…dust and trace gas species have helped quantify densities in the outer parts of circumstellar disks (Kitamura et al. 2002; Andrews & Williams 2007a; Hughes et al. 2008; Isella et al. 2009), clearly established the presence of vertical temperature and density gradients (Dartois et al. 2003; Piétu…”
A dual-frequency sub-arcsecond study of proto-planetary disks at mm wavelengths: first evidence for radial variations of the dust properties (2011, background): “The softened-edge model has recently gained favor because, as suggested by Hughes et al. (2008), it may provide a framework that can explain both the continuum and optically thick CO emission.”
Dust properties of protoplanetary disks in the Taurus-Auriga star forming region from millimeter wavelengths (2009, background): “…that different interferometric observations performed on the same disk can lead to very different values of Rout (≥ 100 AU) because 4 As shown by Hughes et al. (2008) and Isella et al. (2009), a tapered exponential edge in the surface density profile, physically motivated by the viscous…”
The warm gas atmosphere of the HD 100546 disk seen by Herschel - Evidence of a gas-rich, carbon-poor atmosphere? (2012, background): “In other disks, Hughes et al. (2008) found that CO J = 3−2 can be more clearly explained when such a exponential cutoff is used.”