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Young Jupiters are Faint. Jonathan Fortney (NASA Ames) Mark Marley (Ames) , Olenka Hubickyj (Ames/UCSC) , Peter Bodenheimer (UCSC) , Didier Saumon (LANL). Don Davis. Review evolution at young ages Nucleated collapse models (Core accretion – Gas capture) Alternate early evolution

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young jupiters are faint
Young Jupiters are Faint
  • Jonathan Fortney (NASA Ames)
  • Mark Marley (Ames), Olenka Hubickyj (Ames/UCSC),
  • Peter Bodenheimer (UCSC), Didier Saumon (LANL)

Don Davis

slide2
Review evolution at young ages
  • Nucleated collapse models (Core accretion – Gas capture)
  • Alternate early evolution
  • Other detectability issues
slide3

“Arbitrarily Hot Start”

Teff (K)

log Age (Gyr)

Burrows et al. 2001

early model evolution
Early Model Evolution
  • Initial conditions are uncertain
    • initial radii too large for smallest masses
    • collapse & accretion not spherical
  • “...assigning an age to objects younger than a few Myr is totally meaningless when the age is based on models using oversimplified initial conditions.” Baraffe et al. (2003)
  • When can the models be trusted?
  • Can initial conditions be improved?
nucleated collapse model
Nucleated Collapse Model
  • Model for accretion of giant planets
    • 10 to 20 M⊕core forms first, initiates collapse of nebula
    • Time to gas runaway sensitively depends on atmospheric opacity
    • Peak accretion luminosity, created by shock, is short lived
    • Gives initial boundary condition for subsequent evolution

Hubickyj, Bodenheimer & Lissauer (2005)

slide10

How long is the formation time?

  • Opacity of proto-atmosphere affects formation time, as does surface density of the nebula
  • Only Podolak (2003) has tried to calculate the opacity of the proto-atmospheres during formation
  • When does t = 0?
  • Agreement with standard cooling models is even worse if one assigns t=0 to the post-formation time

Hubickyj, et al (2005)

a potential application 2m1207 companion
A Potential Application: 2M1207 Companion
  • Companion to ~M8 brown dwarf in TW Hydrae (age ~ 8 Myr)
  • red J-K implies late L, Teff ~ 1250 K
  • Models give M = 5 ± 2 MJup

Chauvin et al. (2004)

slide12

Teff (K)

log Age (Gyr)

Burrows et al. 1997

similar problem for other objects
Similar Problem for Other Objects?

AB Dor C

Reiners et al. (2005) – young M star

Close et al. (2005) – young M star

Mohanty et al. (2004a,b)

Comparisons with hi-res spectra

Masses down to deuterium burning limit

Zapatero Osorio et al. (2004)

Dynamical masses of GJ 569 Bab brown dwarfs

moral

SOri70

Moral
  • Discern mass from g, Teff indicators in spectra & colors, not luminosity at young ages (This was just done for GQ Lup b)
  • (Of course, this isn’t always easy…)

log g = 5.5

log g = 4

from Knapp et al. (2004)

slide16

Which Bandpasses to Search?

Jupiter’s M band flux has stories to tell!

M band Jupiter image courtesy Glenn Orton

conclusions
Conclusions
  • Luminosity of young giant planets depends sensitively on initial conditions
  • Nucleated collapse models are cooler, dimmer, and smaller than generic ‘hot start’ evolution calculations. Differences...
    • persist longer than “a few million years”
    • are more significant at larger masses
  • Use of ‘hot start’ evolution may result in substantially underestimating mass of observed objects, depending on actual formation mechanism
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