Dust coagulation in protoplanetary disks: A rapid depletion of small grains

By C. Dullemond, C. Dominik. 2004

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We model the process of dust coagulation in protoplanetary disks and calculate how it affects their observational appearance. Our model involves the detailed solution of the coagulation equation at every location in the disk. At regular time intervals we feed the resulting 3D dust distribution functions into a continuum radiative transfer code to obtain spectral energy distributions. We find that, even if only the very basic - and well understood - coagulation mechanisms are included, the process of grain growth is much too quick to be consistent with infrared observations of T Tauri disks. Small grains are removed so efficiently that, long before the disk reaches an age of 10 6 years typical of T Tauri stars, the SED shows only very weak infrared excess. This is inconsistent with observed SEDs of most classical T Tauri stars. Small grains must be replenished, for instance by aggregate fragmentation through high-speed collisions. A very simplified calculation shows that when aggregate fragmentation is included, a quasi-stationary grain size distribution is obtained in which growth and fragmentation are in equilibrium. This quasi-stationary state may last 10 6 years or even longer, depending on the circumstances in the disk, and may bring the time scales into the right regime. If this is indeed the case, or if other processes are responsible for the replenishment of small grains, then the typical grain sizes inferred from infrared spectral features of T Tauri disks do not necessarily reflect the age of the system (small grains → young, larger grains → older), as is often proposed. Indeed, there is evidence reported in the literature that the typical inferred grain sizes do not correlate with the age of the star. Instead, it is more likely that the typical grain sizes found in T Tauri star (and Herbig Ae/Be star and Brown Dwarf) disks reflect the state of the disk in some more complicated way, e.g. the strength of the turbulence, the amount of dust mass transformed into planetesimals, the amount of gas lost via evaporation etc. A simple evolutionary scenario in which grains slowly grow from pristine 0.1 µm grains to larger grains over a period of a few Myr is most likely incorrect.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/409c143f60b3e0dc67f145456f98b03ddf840b3e

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Citations in the corpus

Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA (2015, background): “…of the gas inside the dust hole is essential to distinguish between the possible clearing mechanisms of the dust in the inner part of disk: photoevaporation (Clarke et al. 2001), grain growth (Dullemond & Dominik 2005), clearing by (sub)stellar or planetary companions (e.g. Lin & Papaloizou 1979).”
Dust filtration at gap edges: Implications for the spectral energy distributions of discs with embedded planets (2006, methodology): “It is also likely that in this case, grain coagulation would soon produce large grains in the inner disc (Dullemond & Dominik 2005).”
Volatile carbon locking and release in protoplanetary disks. A study of TW Hya and HD 100546 (2016, background): “The dust growth timescale may be substantially shorter than this (e.g. Dullemond & Dominik 2005), in which case ∆X > 0.21 in the past.”
Dust Evolution and the Formation of Planetesimals (2016, background): “21), then ȧ = ρd π √ 12 kB T ρ3s︸︷︷︸ :=A a−3/2, (25) which can be integrated to (e.g., Dullemond & Dominik 2005) a(t) = [ a(t0) 5/2 + 5 2 A t ]2/5 .”
Trapping dust particles in the outer regions of protoplanetary disks (2011, background): “…aimed to explain theoretically the growth from small dust particles to planetesimals, which have led to the development of different numerical models, e.g. Nakagawa et al. (1981), Dullemond & Dominik (2005), Brauer et al. (2008), Zsom & Dullemond (2008), Okuzumi (2009), Birnstiel et al. (2010a).”
Size-sorting dust grains in the surface layers of protoplanetary disks (2008, unknown): “However, such a trivial, direct connection seems rather unlikely, given the speed at which coagulation can proceed and produce large dust grains (Dullemond & Dominik 2005).”
A SPATIALLY RESOLVED INNER HOLE IN THE DISK AROUND GM AURIGAE (2009, background): “This would produce a drop in opacities associated only with the inefficiency of emission of large grains at the observed wavelengths (e.g. Strom et al. 1989; Dullemond & Dominik 2005).”
The Spitzer c2d Survey of Weak-Line T Tauri Stars. II. New Constraints on the Timescale for Planet Building (2007, methodology): “A simple disk evolution scenario based solely on dust grain growth and settling predicts smaller αexcess slopes for longer λturn−off or larger cleared inner regions (Dullemond & Dominik 2005, D’Alessio et al. 2005).”
Breaking through: The effects of a velocity distribution on barriers to dust growth (2012, background): “In the classic scenario, this happens by the way of incremental growth, in which sticking collisions lead to successively larger aggregates (Weidenschilling 1997; Dullemond & Dominik 2005).”
UNVEILING THE STRUCTURE OF PRE-TRANSITIONAL DISKS (2010, background): “Grain growth simulations predict that dust will evolve on faster timescales in the inner parts of the disk, and eventually the small grains which contribute to the near-IR emission of the disk will grow causing a flux deficit in the SED (Dullemond & Dominik 2004, 2005).”
Planet Formation around Stars of Various Masses: The Snow Line and the Frequency of Giant Planets (2007, background): “…in ∼105 yr (based on an infall rate of 10−5 M⊙ yr−1, Palla & Stahler 1999), and that planetesimal formation is relatively fast (Weidenschilling 2000; Dullemond & Dominik 2005), we add a constant offset of 105 yr to the isolation timescale to reconcile the timing of isolation with disk and…”
Forming Planetesimals in Solar and Extrasolar Nebulae (2009, background): “eﬃcient is expanded νd(Σ) = νd(Σ0) + dνd/dΣ|0 Σ ′ . (34) A non-zero drift v0 is necessary for perturbations to νd to enter linearly. The dispersion relation reads Γ = ν0 2 −1 +2ı˜k ± q 1−4ıδν˜k , (35) where ˜k ≡ kv0/ν0 and δν ≡ dln νd/dlnΣ| 0. For any δν 6= 0 the positive root gives growth, since ”
Evidence for the formation of comet 67P/Churyumov-Gerasimenko through gravitational collapse of a bound clump of pebbles (2017, background): “Visible and near-infrared observations of mostly scattered stellar light are sensitive to µm-sized dust and show the presence of these particles in PPDs of all ages (see, e.g., the discussion in Dullemond & Dominik 2005).”
Survival of molecular gas in cavities of transition disks - I. CO (2013, background): “Pure graingrowth on the other hand (e.g. Dullemond & Dominik 2005; Birnstiel et al. 2012a) should not alter the gas structure much (δgas ∼ 1).”
STRUCTURE AND EVOLUTION OF PRE-MAIN-SEQUENCE CIRCUMSTELLAR DISKS (2009, background): “Until now, photoevaporation, the presence 12 of a planet, grain growth and inside-out MRI clearing have been the main processes invoked to explain the properties of transitional disks (Alexander et al. 2006; Calvet 2005; Espaillat et al. 2008; Dullemond & Dominik 2005; Chiang & Murray-Clay 2007).”
RESOLVED IMAGES OF LARGE CAVITIES IN PROTOPLANETARY TRANSITION DISKS (2011, background): “For example, models of the grain size evolution in disks predict smooth κ variations (Dullemond & Dominik 2005; Garaud 2007; Brauer et al. 2008; Birnstiel et al. 2010), rather than the abrupt optical depth change near Rcav that is observed.”
Planetesimal formation by sweep-up: how the bouncing barrier can be beneficial to growth (2012, background): “At these large collision energies, the particles tend to fragment rather thanstick (Blum & Wurm 2008), which effectively prevents further growth (Dullemond & Dominik 2005; Brauer et al. 2008; Birnstiel et al. 2010).”