The Insignificance of P-R drag in detectable extrasolar planetesimal belts

By M. C. Wyatt. 2005

160 citations recorded by the source corpus.

This paper considers a simple model in which dust produced in a planetesimal belt migrates in toward the star due to P-R drag suffering destructive collisions with other dust grains on the way. Assuming the dust is all of the same size, the resulting surface density distribution can be derived analytically and depends only on the parameter η0 = 5000τeff (r0) √ M� /r0/β; this parameter can be determined observationally with the hypothesis that β = 0.5. For massive belts in which η0 � 1 dust is confined to the planetesimal belt, while the surface density of more tenuous belts, in which η0 � 1, is constant with distance from the star. The emission spectrum of dust from planetesimal belts at different distances from different mass stars shows that the dust belts which have been detected to date should have η0 � 1; dust belts with η0 � 1 are hard to detect as they are much fainter than the stellar photosphere. This is confirmed for a sample of 37 debris disk candidates for which η0 was determined to be >10. This means that these disks are so massive that mutual collisions prevent dust from reaching the inner regions of these systems and P-R drag can be ignored when studying their dynamics. Models for the formation of structure in debris disks by the trapping of particles into planetary resonances by P-R drag should be reconsidered. However, since collisions do not halt 100% of the dust, this means that in the absence of planetary companions debris disk systems should be populated by small quantities of hot dust which may be detectable in the mid-IR. Even in disks with η0 � 1 the temperature of dust emission is shown to be a reliable tracer of the planetesimal distribution meaning that inner holes in the dust distribution imply a lack of colliding planetesimals in the inner regions.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/499699a9515a4f64f6975f9c3d4d9d73de122011

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Citations in the corpus

Dust Dynamics, Surface Brightness Profiles, and Thermal Spectra of Debris Disks: The Case of AU Microscopii (2005, unknown): “Similar classifications were put forward by Wyatt (2005) and Meyer et al. (2006) in their considerations of disks composed of single-sized grains.”
Debris disc stirring by secular perturbations from giant planets (2009, background): “The dust grains have only a short lifetime compared to the ageof the star, being ground down in collisional processes until they are small enough to be ejected from the system by radiation pressu (Dominik & Decin 2003; Wyatt 2005).”
COMETARY ORIGIN OF THE ZODIACAL CLOUD AND CARBONACEOUS MICROMETEORITES. IMPLICATIONS FOR HOT DEBRIS DISKS (2009, background): “Being dominated by collisions (as opposed to PR drag regime; see Wyatt 2005), the trans-planetary particles are destroyed before they could evolve to R < 20 AU.”
FOMALHAUT'S DEBRIS DISK AND PLANET: CONSTRAINING THE MASS OF FOMALHAUT B FROM DISK MORPHOLOGY (2008, background): “In practice, for many debris disks, the first two channels are more important than the fourth (Wyatt 2005; Strubbe & Chiang 2006; Thébault & Wu 2008).”
Predictions for a planet just inside Fomalhaut's eccentric ring (2006, methodology): “As this time-scale is short, we can exclude Poynting–Robertson driven resonance capture models for the dust, as argued in detail by Wyatt (2005).”
NEW DEBRIS DISKS AROUND YOUNG, LOW-MASS STARS DISCOVERED WITH THE SPITZER SPACE TELESCOPE (2009, unknown): “…in Hillenbrand et al. (2008); Krivov (2007); Krivov et al. (2007, 2006); Strubbe & Chiang (2006); Minato et al. (2006); Najita & Williams (2005); Plavchan et al. (2005); Chen et al. (2005a); Wyatt (2005, 2003); Dominik & Decin (2003); Jura et al. (1995); Gustafson (1994); Backman & Paresce (1993).”
Nearby Debris Disk Systems with High Fractional Luminosity Reconsidered (2006, background): “It is predicted that in disks with fd > 10 4 the evolution is dominated by collisions (Dominik & Decin 2003; Wyatt 2005).”
Transience of Hot Dust around Sun-like Stars (2006, background): “This is not the case, how- 4 In planetesimal belts as tenuous as the asteroid belt, the effect of P-R drag is important (Wyatt 2005) meaning that the crosssectional area of dust in the zodiacal cloud is dominated by ∼ 100 µm sized grains rather than grains of size Dbl as assumed in the simple model…”
Debris Disks in Main-Sequence Binary Systems (2006, background): “, where PR is in yr; r is the radial distance to be crossed, in AU;M? is in solar masses; and is as defined above TRILLING ET AL.1304 Vol. 658 (Wyatt 2005).”
Long-Term Collisional Evolution of Debris Disks (2007, background): “Tenuous disks, where the lifetime of dust grains is not limited by collisions but by transport processes like the Poynting-Robertson drag (Artymowicz 1997; Krivov et al. 2000; Wyatt 2005), follow M ∝ t−2 rather thanM ∝ t−1.”
Steady State Evolution of Debris Disks around A Stars (2007, background): “/β 1 (Wyatt 2005), where β is the ratio of the radiation force to that of gravity of the star, since this is when the collisional lifetime of the dust is equal to the time it would take to reach the star by the drag force.”
FORMATION AND EVOLUTION OF PLANETARY SYSTEMS: PROPERTIES OF DEBRIS DUST AROUND SOLAR-TYPE STARS (2008, unknown): “For debris disks detectable with current instrumentation, Dominik & Decin (2003) demon- strated that collisional processes combined with radiation pressure dominate over PoyntingRobertson drag in removing dust grains from the system (see also Wyatt 2005).”
Spitzer IRS Spectroscopy of IRAS-discovered Debris Disks (2006, background): “Recently, Wyatt (2005) concluded that PR drag is relatively unimportant in IRAS -discovered debris disks.”
The Complete Census of 70 μm-Bright Debris Disks within “The Formation and Evolution of Planetary Systems” Spitzer Legacy Survey of Sun-like Stars (2007, background): “Similar analysis by Dominik & Decin (2003) and Wyatt (2005) of previously known bright debris disks has led to similar conclusions: that they are all collision dominated.”
Dust distributions in debris disks: effects of gravity, radiation pressure and collisions (2006, methodology): “If τ > 10−5 (all observable extrasolar disks), P-R drag is inefficient, as the collisional lifetimes are much shorter than the P-R times (Krivov et al. 2000; Wyatt 2005).”
Debris disks as signposts of terrestrial planet formation (2011, background): “This distribution spans from the smallest assumed particles Dbl = 2.2 μm up to the largest Dc = 2000 km. Smaller particles than Dbl are assumed to be blown out of the system by radiation pressure on short enough timescales to not contribute to the size distribution (see, e.g., Wyatt 2005).”
Variations on Debris Disks: Icy Planet Formation at 30-150 AU for 1-3 M☉ Main-Sequence Stars (2008, background): “Initially, collisions dominate Poynting-Robertson drag; thus, radiation pressure ejects the smallest grains on the local orbital timescale (e.g., Krivov et al. 2000; Wyatt 2005).”