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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. Review evolution at young ages Nucleated collapse models (Core accretion – Gas capture) Alternate early evolution

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Young Jupiters are Faint

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  1. Young Jupiters are Faint • Jonathan Fortney (NASA Ames) • Mark Marley (Ames), Olenka Hubickyj (Ames/UCSC), • Peter Bodenheimer (UCSC), Didier Saumon (LANL) Don Davis

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

  3. “Arbitrarily Hot Start” Teff (K) log Age (Gyr) Burrows et al. 2001

  4. 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?

  5. 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)

  6. Deviations are greater at larger masses

  7. Arbitrarily hot start overestimates radius and under- estimate gravity at all masses

  8. 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)

  9. 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)

  10. Teff (K) log Age (Gyr) Burrows et al. 1997

  11. Real mass closer to 10 MJ ?

  12. 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

  13. 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)

  14. Which Bandpasses to Search? Jupiter’s M band flux has stories to tell! M band Jupiter image courtesy Glenn Orton

  15. Nonequilibrium CO dims M band Saumon et al. 2003

  16. Saumon et al. 2003

  17. L’ May Be Comparable to M’ L’

  18. 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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