Young Jupiters are Faint

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

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Arbitrarily Hot Start
Teff (K)
log Age (Gyr)
Burrows et al. 2001
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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?

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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)
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Deviations are greater at larger masses
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Arbitrarily hot start overestimates radius and
under- estimate gravity at all masses
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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 t0 to the post-formation
  time

Hubickyj, et al (2005)
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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)
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Teff (K)
log Age (Gyr)
Burrows et al. 1997
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Real mass closer to 10 MJ ?
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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
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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 isnt always easy)

log g 5.5
log g 4
from Knapp et al. (2004)
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Which Bandpasses to Search?
Jupiters M band flux has stories to tell!
M band Jupiter image courtesy Glenn Orton
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Nonequilibrium CO dims M band
Saumon et al. 2003
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Saumon et al. 2003
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L May Be Comparable to M
L
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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