Debris Disks: Probing Planet Formation

Abstract

Debris disks are the dust disks found around ∼ 20% of nearby main sequence stars in far-IR surveys. They can be considered as descendants of protoplanetary disks or components of planetary systems, providing valuable information on circumstellar disk evolution and the outcome of planet formation. The debris disk population can be explained by the steady collisional erosion of planetesimal belts; population models constrain where (10-100 au) and in what quantity (> 1M ⊕ ) planetesimals (> 10 km in size) typically form in protoplanetary disks. Gas is now seen long into the debris disk phase. Some of this is secondary implying planetesimals have a Solar System comet-like composition, but some systems may retain primordial gas. Ongoing planet formation processes are invoked for some debris disks, such as the continued growth of dwarf planets in an unstirred disk, or the growth of terrestrial planets through giant impacts. Planets imprint structure on debris disks in many ways; images of gaps, clumps, warps, eccentricities and other disk asymmetries, are readily explained by planets at 5 au. Hot dust in the region planets are commonly found (< 5 au) is seen for a growing number of stars. This dust usually originates in an outer belt (e.g., from exocomets), although an asteroid belt or recent collision is sometimes inferred.

The REASONS Survey: Resolved Millimeter Observations of a Large Debris Disk around the Nearby F Star HD 170773

“…The REASONS (REsolved ALMA and SMA Observations of Nearby Stars) survey, the follow up of the JCMT SCUBA-2 Observations of Nearby Stars (SONS) Legacy survey (Holland et al 2017), aims to approximately double the sample size of millimeter-resolved debris disks. We present new 1.3 mm observations of the debris disk around the nearby (37.02 ± 0.06 pc: Bailer-Jones et al 2018;Gaia Collaboration et al 2016, 2018 F5V (Gray et al 2006) star HD 170773. The infrared excess of HD 170773 was first detected by Sadakane & Nishida (1986) with IRAS, which is a general indication that a debris disk might be present in the system.…”

“…The stellar parameters of HD 170773, i.e., age, mass, luminosity, effective temperature, surface gravity, and radius, were inferred by employing the absolute G magnitude (6.1040±0.0004 mag, obtained from the apparent G magnitude and the parallax) and BP−RP color from Gaia DR2 (0.5691±0.0059 mag, Gaia Collaboration et al 2016Collaboration et al , 2018Lindegren et al 2016), as well as [Fe/H] (assumed to be solar, 0.0 ± 0.20 dex), all three as input parameters using the Bayesian approach applied in del Burgo & Allende Prieto (2016, 2018. We inferred that HD 170773 is most likely a main sequence star and show the derived parameters in Table 4.…”

Debris Disks in Multiplanet Systems: Are Our Inferences Compromised by Unseen Planets?

“…In another type of resonant interaction, a planet captures planetesimals into its orbital resonances while migrating and redistributes the planetesimals to certain longitudes, creating an azimuthal asymmetry in the disk. Properties of these resonant disk features (e.g., the gap width or the shape of clumpy features) can be used to constrain the sculpting planet's mass, semi-major axis, and migration history (Wisdom 1980;Quillen 2006;Wyatt 2018). Here we investigate if/how our inferences of these planet properties are compromised using a single-planet model when multiple planets reside in the system for edges and gaps (Section 3.1) and azimuthal asymmetries (Section 3.2).…”

“…With an initial semi-major axis of 40 au for planet b (a 0,b = 40 au), this evolution means planet b migrates from 40 au to 66 au over 10 Myr. The migration rate we use here is motivated by Wyatt (2003) to optimize the capture probabilities into the 3:2 resonance for planetesimals. Three different initial semi-major axes of planet c are investigated: a 0,c = 36 au, a 0,c = 30.5 au, and a 0,c = 25 au, which correspond to final semi-major axes of 59.4 au, 50.3 au, and 41.2 au, respectively.…”

“…A debris disk, a circumstellar disk of dust and planetesimals orbiting its host star, has been detected around roughly 17-20% solartype stars (Sibthorpe et al 2018;Hughes et al 2018, and references therein). The dust in a debris disk is continuously produced through collisions of planetesimals that are gravitationally redistributed by the posited underlying planets (Wyatt 2008). By investigating debris disk features (here we focus on warps, offsets, edges and gaps, azimuthal asymmetries, radially thickened rings, scale heights) induced by planet-disk interactions, we can characterize the corresponding planetary system properties, such as the planet mass, its orbital parameters, and the timescale expected for a disk to evolve the observed features (see Hughes et al 2018, and references therein).…”