Conference notes

Posted by Simon Walker on Mon 10 June 2013

This is not a blog post as such, it's the notes that I took during the conference split up into sections. Unfortunately there is no reference to the talk content itself; this is kept in the booklet which I have sitting next to me as I type this.

Session 1

Detecting and characterising via direct imaging

  • More than 2Gyr gas giants more than 10^8 times fainter than primary
  • Young stars are 10^4 - 10^7 times better than this
  • Chronograph for increasing contrast
  • Speckle noise a big problem
    • for speckle based data S/N does not increase with time
    • angular differential imaging
      • speckles oscillate while image rotates, but keep similar shape
      • real objects will move in the frame
  • A stars good targets despite being bright
    • higher hosting fraction for giant planets for A stars (not sure about this)
    • high profile detections
    • Nielsen show low host fraction despite this
  • M stars also good targets
    • despite low independent host fraction
  • Typical contrasts - 10^5 at 1 arcsecond (with NICI)

Physical properties (atmospheres)

  • Direct photons detected from these objects
    • reflected light and background contaminants surely?
  • Colours in infra-red shows deviations from the predicted T dwarf type sequence (brightness vs colour)
    • more like L dwarfs
    • much lower surface gravity
  • Direct spectra taken (!)
  • Huge spectral diversity for planets even in same system
  • Surface gravity strongly affecting the spectra
  • Orbits of Beta Pic 2 - Chauvin et al. 2012
    • most probable semi major axis


  • Upper limits to abundance
  • Cold start - less than 10% for separations 20 - 630 AU
  • Hot start - less than 10% for separations 10 - 810 AU
  • Gravitational instability planets rare at more than 10 AU
  • Scattering planets also rare
  • Sphere project - 10 - 80 more planets
  • Possible detection of Super-Earth around nearby M dwarf (Crossfield, Goyon et al. 2013)


  • Young exoplanets have red colours consistent with dusty clouds and non-equilibrium chemistry
  • Hot start gas giant planets more than 4 MJup rare at more than 10AU

International deep planet survey

  • Homogeneous analysis methods


  • Strategic Explorations of Exoplanets and discs with Subaru
  • Variety in morphology of protoplanetary discs
    • gaps, non-uniform shapes
  • IRD - IR doppler instrument on Subaru
    • could be good for follow up for NGTS, investigate this
    • paper

Hershell dust evolution in discs

  • SED modelling and Herschel tracing dust evolution in discs

Planet formation in evolving protoplanetary discs

  • Gas dominates planetary formation
  • Planets form in evolving discs
  • Disc dispersal quick and efficient
    • relatively few systems found with partial discs
  • Accretion in disc core, with photoevaporation at higher disc heights
  • Changes in disc structure can form traps for dust or planets
  • Final gas disc dispersal halts planet migration
  • Giant planet migration can be halted if the disc gas is dispersed
  • RDA & Armitage 2009, RDA and Pascucci 2012
  • Pile up observed in models and data at 1-2AU
    • looks like a possible pile up at smaller separations also

Disc inhomogeneities and the origins of planetary system architectures and observational properties

  • Discs have 3 types of planet trap

HST/STIS imaging of Fomaulhaut: New main belt structure and confirmation of Fomalhaut b’s eccentric orbit

  • Highly eccentric 0.8
  • A ~= 1.77
  • Periastron: 32AU
  • P ~= 1700 years
  • Dynamically linked with belt
    • mutual inclination (planet - belt) ~ 17 degrees
    • Periastron linked
  • Gap in main belt of ~50AU
  • Inner belt detected
  • Planet planet scattering: Chatterjee et al. 2008

Highlights of Exoplanet Characterization

  • Planets are diverse in Teff(planet) vs IR colour, no clear pattern yet
  • Uranus and Neptune heavily enriched in carbon (50x)
    • also very old, about 50K
  • Consistent non-detection of CO in GJ436
  • Featureless atmosphere of GJ1214b suggests high mean molecular weight
    • dramatic cloud obscuration
    • high water constituent
  • Low mass planets may have high Zenv (metal fraction of the envelope)
  • GJ3470b - Uranus analogue
  • GJ436b has dayside and transit data breaking atmospheric degeneracy
  • Comparisons of C/O ratio for star and planet v. interesting

Planets around low mass stars (PALMS) high contrast imaging survey

  • Link with microlensing
  • Snapshot program - breadth not width
  • Gravity-dependant L to T dwarf transition

Session 2


  • Radio maps more than 95% of mass
    • good for structure

Triggered planet formation in action: resolved gas and dust images of a transitional disk and its activity

  • Surface density excess after a planetary body traps large dust particles in a potential maximum
  • Increased density leads to planet formation

Session 3

Review - The story of planets: anchoring numerics to reality

  • Hubble protoplanetary disk atlas - nice pictures
  • Disc gaps depend on grain size - different wavelengths probe grain size and gap width
  • Grain growth drives planetessimal (~km sized) formation
    • not reliable
  • Pairwise accretion - slow, turbulence high, has issues
    • requires velocity dispersion/distribution in simulations
      • mean velocity is not enough for an accurate simulation
    • requires grain size distribution
  • Pressure bumps trap dust
    • leads to further processes, gravitational instability, accretion
  • Accretion very low fraction of simulated collisions
  • Dust distribution dependant on planetessimal eccentricity

Zooming in on protoplanetary discs

  • Magnetic fields in star forming region does not create planar disc initially
    • vertical structure is created
  • Free-fall accretion guided by magnetic field

Planetessimal formation

  • Disc cross section
    • core stable
    • edges suffer instability
  • Planet trend with instability
    • mostly requires local Disk metalicity, could be super-solar

Session 5

A decade and a half of AngloAustralian Planet Searching

  • 240 stars sample over 15 years
  • 2.5 meters per second precision
  • HD 20782 - highest eccentricity 0.952
  • Wittenmyer et al., 2011, apj - reference for false rv signal testing
  • R ~ 60000 - S/N needs to be 5000
  • FunnelWeb - spectra of all stars V less than 12, delta less than 20, 390-800nm Very nice talk

The Debiased Kuiper Belt: Our Solar System as a Debris disc

  • 20% large KBOs more than 100km are in resonance with Neptune

Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system

  • Active granulation effects for RV
    • bright blue cells dominate cool red cells = net blueshift
    • creates RV signal of ~ 1m/s
  • Use lightcurve without transits to provide activity profile
    • simultaneous observations
    • RV profile then contains both stellar noise and planet
    • use lightcurve as basis function

Properties of the young gas giant planet Beta Pictoris b

  • Planet on inclined orbit around star, inclined wrt disc

Characterizing the Demographics of Exoplanet Bulk Compositions

  • New kepler mass radius relations with Keck

Unveiling an exoplanetary Neptunian atmosphere through multiband transit photometry

  • Infra-red used to measure bands H2O, CO, CH4

The Shocking Variability of Exoplanet Transits

  • WASP-12 b bow shock in the infra-red

Session 6

Debris discs as components of extrasolar planetary systems

  • Debris disc descendant of protoplanetary disc
  • Proplyds
    • less than 10MYr
    • optically thick
    • more than 10 Mearth
    • ~100x dust mass
    • dust from 0.1-100AU
    • primordial?
  • Debris

    • 10MYr -10Gyr
    • optically thin
    • less than 1 MEarth
    • no gas
    • ~30AU ring
  • Inner holes caused by planets?

  • Inner edge of disc predicted to be carved by planets
    • shape of the edge depicted by planet mass
  • CO short lifetime ~100 years due to photo-disassociation
  • Clump in disc
    • could be through planet orbit and gravitaitonal influence
    • could be a destruction event causing debris to pass through the same point leading to higher density
  • Alma probes mm sized dust - traces planetessimals
  • Scattered light probes micron sized dust
  • Systems with planets are brighter (SKARPS, Herschel) than systems without implying debris discs

A Resolved Millimeter Emission Belt in the AU Mic Debris disc

  • Best fit model suggests increasing surface density with radial distance
    • inner collision depletion?

Detailed model of the exozodiacal disc of Fomalhaut and its origin

Final Results of the Herschel Open Time Key Programme DUNES

  • 16 resolved discs, 13 new

Session 7


  • Morbidelli+ 2009, planetessimal simulation
  • Rafikov 2004, proposed explanation of accelerated core accretion
    • neptune in less than 10Myr

Rapid growth of giant planet cores by pebble accretion

  • Pebble accretion can rapidly grow the planet mass and deal with collapse, according to the model
  • Author: Lambrechts

Planet Formation and Evolution in Traps: Origins of the MassPeriod Relation

  • Traps catch planets while forming
  • Rapid envelope accretion process
  • Model predicts that super earths are failed jovian cores
  • Putdritz model looks interesting
    • predictions for hot Jupiter formation
  • Giant planets start at greater than 0.7Msolar

Session 8 - evolution of planetary systems


  • Interesting deficit of period ratios in Kepler dataset just below 2:1
  • Resonances cause oscillations of the periastron points of a multiple system
    • non-resonances cause circulation
  • If the system is not stable with aligned systems (angle of periastrons equal) then all other configurations will be unstable
  • No close encounter required
  • Hill radius associated with circular orbits
  • Dissipation acts to stabilise systems
  • HAT-P-13 is multiple planet system
    • why does WASP not find any?
    • consider changing wasp pipeline to subtract the in-transit data and re-perform search N times
  • MMR Lithwick
  • Could the Kepler distance from pure resonances be due to unseen non-transiting bodies?

Constraining planetary migration mechanisms in systems of giant planets

  • Dawson and Johnson 2012 - predicting eccentricity from Kepler lightcurves
  • Metal-poor and metal-rich lead to disk migration
    • only metal rich stars form multiple systems
  • Fressin et al. 2013 - kepler occurrence rates
  • Possible pile up at short periods for metal rich Kepler host stars
  • How do eccentric planets in the period valley between 0.1 and 1 AU form?
  • Planet planet scattering possibly ejecting outer planet removing it from evidence for it

The Impact of Stellar Multiplicity on Planetary Systems

  • High protoplanetary disc occurrence for wide binary planets
    • distinct decrease below binary star separations of ~40AU
  • Similarly decreasing disc mass with decreasing orbital separation
  • RV surveys biased against binary stars due to the stray light from the binary companion in the slit
  • Only equal flux binaries at short separations
    • selection effect?
      • maybe planets form around the fainter secondary and are therefore harder to detect so we don't find them

Orbital structure of Kepler Planetary Systems

  • Low mass planets targeted for the talk
    • less than ~30Mearth
  • Fortney 07 density structures
  • Bimodal small radius distribution
    • can be split by the x-ray exposure
  • TTV mass estimations extremely sensitive to eccentricity

Archaeology of Exo-Terrestrial Planetary Systems

  • RECONS project - spectral types within 10pc

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