On the Frequency of Gas Giant Planets in

On the Frequency of Gas Giant Planets in the Metal-Poor Regime Alessandro Sozzetti 1, D. W. Latham 2, G. Torres 2, R. P. Stefanik 2, S. G. Korzennik 2, A. P. Boss 3, B. W. Carney 4, J. B. Laird 5 (1) INAF/OATo - (2) Cf. A - (3) CIW - (4) UNC - (5) BGSU Pisa, 6 May 2009

Core Accretion & Disk Instability * Core Accretion: Bottom-Up! Accumulate a 10 M core (dust to planetesimals to runaway accretion), which accretes a massive gaseous envelope from the disk. * Disk Instability: Top-Down! Local gravitational collapse of a gaseous portion of the disk leads to a Jupiter-mass (or larger) protoplanet. The rocky core is formed almost simultaneously by sedimentation of dust grains to the center. Boss (SSRv, 2005) Pisa, 6 May 2009

Do giant planets form by Core Accretion, Disk Instability, or both? Ida & Lin (Ap. J, 2004), Kornet et al. (A&A, 2006): “The frequency of giant planet formation by core accretion is roughly a linear function of Z” Boss (Ap. JL, 2002): “The frequency of giant planet formation by disk instability is remarkably insensitive to Z” N/A Pisa, 6 May 2009

Globular Cluster 47 Tucanae 11 Gyr, 106 stars [Fe/H] ~ - 0. 7 HST/WFPC 2 HST (WFPC 2) observed about 34, 000 stars in 47 Tuc, obtaining time series photometry over a period of 8. 3 days No planet eclipses were seen. Gilliland et. al. (Ap. J 2000), Weldrake et al. (Ap. J 2005) Pisa, 6 May 2009

However… • Crowding can impact giant planet formation, migration, and survival • The absence of Hot Jupiters in a metal-poor environment does not imply they don’t exist at larger radii GCs are not optimal Go to the field Pisa, 6 May 2009

Fp vs [Fe/H] Linear Dependence? Flat tail for [Fe/H] < 0. 0? Low statistics for [Fe/H] < -0. 5 Santos et al. (A&A, 2004): No P, K, [Fe/H] thresholds: Quadratic dependence? Flat tail for [Fe/H]<0. 0? Low statistics for [Fe/H] < -0. 5 Fischer & Valenti (Ap. J, 2005): K > 30 m/s, P < 4 yr, -0. 5<[Fe/H]<0. 5: Fp ~ Z, for Z > 0. 02) Fp ~ const, for Z < 0. 02 Pisa, 6 May 2009

Small-number statistics for [Fe/H] < -0. 5 prevents one from drawing conclusions: Is Fp([Fe/H]) bimodal or monotonic? What is the dominant mode of giant planet formation? Pisa, 6 May 2009

Keck/HIRES Metal-Poor Planet Search • • • 200 stars from the Carney-Latham and Ryan samples No close stellar companions Cut-offs: -2. 0 < [Fe/H] < -0. 6, Teff < 6000 K, V < 12 Reconnaissance for gas giant planets within 2 AU Campaign duration: 3 years Sozzetti et al. (Ap. J, 2006) Pisa, 6 May 2009

The RV dispersion of the full sample peaks at 9 m/s Sozzetti et al. (Ap. J, 2006) Pisa, 6 May 2009

No clear RV trends are seen as a function of Teff, [Fe/H], and ΔT Pisa, 6 May 2009

Analysis: Methodology • Statistical analysis: testing for excess variability (F -test, 2 -test, Kuiper test) • Analysis of long-term (linear and curved) trends • Limits on companion mass and period from detailed simulations • Upper limits on fp and new powerful constraints on fp([Fe/H]) in the metal-poor regime Pisa, 6 May 2009

RV Variables Follow-up About 6% of the stars in the sample have long-period companions Follow-up with direct infrared imaging (MMT/Clio) to determine their nature (low-mass stars or brown dwarfs) Pisa, 6 May 2009

MMT/Clio Imaging @ 5 μm ~1” ~0. 5” ΔM ~ 2. 5 mag ΔM ~ 6. 5 mag Pisa, 6 May 2009

COMPLETENESS: - 6 observations, 3 -yr baseline; - s. RV = 9 m/s - 99. 5% confidence level - Sensitivity to companions with 1 MJ<Mpsin(i)<6 MJ (K > 100 m/s), with orbital periods between a few days and 3 years - Strong dependence of detection thresholds on eccentricity WE FIND NONE… Pisa, 6 May 2009

Frequency of Close-in Companions (-2. 0<[Fe/H]<-0. 6, K > 100 m/s, P < 3 yr, e < 0. 3) For n=0, N=160: For n=1, N=160: Pisa, 6 May 2009

b=0. 99 b=1. 05 Reliability of the Atmospheric Parameters Compare with the SPOCS database: (σ = 134 K) b=0. 89 (σ = 0. 12 dex) (σ = 0. 06 MSUN) Pisa, 6 May 2009

Sozzetti et al. 2009 (Ap. J, in press): K > 100 m/s, P < 3 yr, -1. 0<[Fe/H]<0. 5: Pisa, 6 May 2009

Summary • We observe a dearth of gas giant planets (K > 100 m/s) within 2 AU of metal-poor stars (-2. 0 < [Fe/H] < -0. 6), confirming and extending previous findings • The resulting average planet frequency is Fp< 0. 67% (1σ) • Fp(-1. 0<[Fe/H]<-0. 5) appears to be a factor of several lower than Fp([Fe/H]>0. 0), but it’s indistinguishable from Fp(-0. 5<[Fe/H]<0. 0). • Is Fp([Fe/H]) bimodal or not? It is consistent with being so. However, need larger and better statistics to really discriminate… • 1) Expand the sample size; 2) lower the mass sensitivity threshold; 3) search at longer periods. Next generation RV surveys and future high-precision space-borne astrometric observatories (Gaia, SIM-Lite) will help… Pisa, 6 May 2009