extrasolar planets: a galactic perspective i. neill reid stsci

Extrasolar planets: a Extrasolar planets: a Galactic perspectiveGalactic perspective

I. Neill ReidI. Neill Reid

STScISTScI

STScI 2005 May Symposium

The questionsThe questions

Over 150 extrasolar planets have been discovered since Over 150 extrasolar planets have been discovered since 19951995 -this includes several multiplanet systems-this includes several multiplanet systems

1. Are there any properties (besides [m/H]) that set the 1. Are there any properties (besides [m/H]) that set the parent stars apart from the average disk star?parent stars apart from the average disk star?

2. Given the statistical properties of the parent stars, 2. Given the statistical properties of the parent stars, coupled with our current knowledge of Galactic structure, coupled with our current knowledge of Galactic structure, How common are planetary systems in the Milky Way?How common are planetary systems in the Milky Way?


OutlineOutline

• The Extrasolar Planetary SystemsThe Extrasolar Planetary Systems• Resolved systems?Resolved systems?• The host starsThe host stars• Local stellar populationsLocal stellar populations• Kinematics and planetsKinematics and planets• Filling the GalaxyFilling the Galaxy• Summary and conclusionsSummary and conclusions

See also papers by the Geneva group (Udry et al; Santos et al; See also papers by the Geneva group (Udry et al; Santos et al; Halbwachs, Mayor & Udry; Bodaghee et al) Halbwachs, Mayor & Udry; Bodaghee et al)


The planetsThe planets~143 planets in 143 planets in conventional systems:conventional systems:

~17~17MMJJ > > MM > ~0.067 > ~0.067MMJJ at least 17 multi-planet at least 17 multi-planet systemssystems 1.2 days < P < 8 years1.2 days < P < 8 years 0.015 AU < 0.015 AU < aa < 4.2 AU < 4.2 AU Most systems have high Most systems have high eccentricity orbitseccentricity orbits

How do we know that these How do we know that these are really planets?are really planets?Brown dwarf/M-dwarf Brown dwarf/M-dwarf desertdesert Both low-mass stars and Both low-mass stars and brown dwarfs are extremely brown dwarfs are extremely rare as close (rare as close (aa < 10 AU) < 10 AU) companions of solar-type companions of solar-type starsstars

Solar-type stars at d < 25 pc


2M1207 & GQ Lupi2M1207 & GQ Lupi

TW Hydrae member –TW Hydrae member – ~ 10 ~ 10 Myrs Myrs MMPP ~ 35 ~ 35 MMJ J , , MMSS ~ 2-5 ~ 2-5 MMJ J

D ~ 60 AUD ~ 60 AU

Lupus I member –Lupus I member – ~ 1 Myrs ~ 1 Myrs MMPP ~ 0.45 ~ 0.45 MM⊙⊙, , MMSS ~ 3-40 ~ 3-40 MMJ J

~ 100 AU~ 100 AU


Brown dwarfs or Brown dwarfs or exoplanets?exoplanets?

Both companions lie in the outer regions of the disk – even for 1.7 Both companions lie in the outer regions of the disk – even for 1.7 MM⊙⊙ Pic Pic2M 1207A/B has high mass ratio, q ~ 0.22M 1207A/B has high mass ratio, q ~ 0.2Both are more likely to be brown dwarf companions than Both are more likely to be brown dwarf companions than exoplanets – can provide crucial insight on BD binary formationexoplanets – can provide crucial insight on BD binary formation


The planetary hostsThe planetary hosts

Most hosts are late-F, G or Most hosts are late-F, G or early-K main-sequence early-K main-sequence stars – exceptions:stars – exceptions:2 M dwarfs 2 M dwarfs ~10 giants~10 giants~8 subgiants~8 subgiants

128 from RV surveys128 from RV surveys1 microlensing1 microlensing6 transit surveys6 transit surveys


CompletenessCompleteness

Valenti/Fisher (Keck) Valenti/Fisher (Keck) sample matched sample matched against Hipparcos against Hipparcos datasetdataset~45% complete to ~45% complete to 25pc for solar-type 25pc for solar-type stars (4 < Mstars (4 < MVV < 6) < 6)Most of the `missing’ Most of the `missing’ stars are included in stars are included in the Geneva samplethe Geneva sample


The host stars: distancesThe host stars: distancesOverwhelming majority Overwhelming majority lie within 50 pc lie within 50 pc bright bright stars from radial velocity stars from radial velocity surveys. Stars are drawn surveys. Stars are drawn from local from local representatives of the representatives of the Galactic stellar Galactic stellar populations:populations:1.1. DiskDisk

2.2. Thick diskThick disk3.3. HaloHalo

But not the Bulge ….But not the Bulge ….


The inner & outer halosThe inner & outer halosInner halo forms Inner halo forms through rapid ELS-through rapid ELS-style collapse of the style collapse of the proto-Galactic cloud proto-Galactic cloud at at ~11-13 Gyrs ~11-13 Gyrs

Outer halo forms Outer halo forms through through subsequent (and subsequent (and continuing) continuing) accretion of accretion of satellite galaxies satellite galaxies

Old, non-rotating, metal-poor ( [m/H] < -1) Old, non-rotating, metal-poor ( [m/H] < -1) populationpopulationLocal density of halo stars ~ 2.6 x 10Local density of halo stars ~ 2.6 x 10-4-4 stars pc stars pc--

33 , or 1:400 relative to the disk , or 1:400 relative to the disk~60% of local subdwarfs contributed by inner ~60% of local subdwarfs contributed by inner halohaloNo known planetary systemsNo known planetary systems


The thick disk: densitiesThe thick disk: densities

Flattened, rotating, mildly metal-poor population, identified Flattened, rotating, mildly metal-poor population, identified from analysis of starcounts perpendicular to the Plane.from analysis of starcounts perpendicular to the Plane.Some ambiguity in deriving Some ambiguity in deriving 00 & z & z00, but current analyses , but current analyses favour zfavour z00~900 pc & ~900 pc & 00 ~ 1.0 x 10 ~ 1.0 x 10-2-2 stars pc stars pc-3-3 , or 1:10 , or 1:10 relative to the diskrelative to the disk


Thick disk: kinematics & Thick disk: kinematics & [m/H][m/H]

Joint kinematic/abundance Joint kinematic/abundance analyses by Fuhrmann, analyses by Fuhrmann, Prochaska, Bernsby & others Prochaska, Bernsby & others indicate that thick disk stars indicate that thick disk stars have enhanced [have enhanced [/Fe]/Fe]Limited enrichment from Limited enrichment from Type I SNType I SN Origin in short-lived (1-2 Origin in short-lived (1-2 Gyr) star-forming episodeGyr) star-forming episode

Current concensus favours Current concensus favours formation through disruption formation through disruption and inflation of the initial and inflation of the initial Galactic disk by a major Galactic disk by a major mergermergerHiatus in star formation Hiatus in star formation Addition of low [m/H[ gasAddition of low [m/H[ gasThin disk reformsThin disk reforms


Planets from the thick Planets from the thick disk?disk?

[Ti], [Fe] from Valenti & Fisher (2005) and Bodaghee et al (2003)[Ti], [Fe] from Valenti & Fisher (2005) and Bodaghee et al (2003)3 TD candidates: HD 6434 (0.48 3 TD candidates: HD 6434 (0.48 MMJJ), HD 37124 (0.75 ), HD 37124 (0.75 MMJJ), HD 114762 ), HD 114762 (11 (11 MMJJ) ) 3 intermediate: HD 114729 (0.82 3 intermediate: HD 114729 (0.82 MMJJ), ), CrB (1.04 CrB (1.04 MMJJ), HD 168746 (0.23 ), HD 168746 (0.23 MMJJ) )


The diskThe disk

Valenti & Fisher (2005)

Flattened, rotating population with Flattened, rotating population with 00 ~ 9.0 x 10 ~ 9.0 x 10-2-2 stars pc stars pc-3-3 (90% of (90% of SN) Double exponential density law: zSN) Double exponential density law: z00~300 pc, h~300 pc, h00~2,500 pc ~2,500 pc Substantial dispersion in [m/H] at any given age – indication of Substantial dispersion in [m/H] at any given age – indication of broad age-metallicity relation broad age-metallicity relation

Haywood (2002)


Host star propertiesHost star properties

1. Clear correlation between [m/H] and planetary frequency

2. No obvious correlation between M* and MP , (although Gl 436 & 876 have low-mass planets).

3. No obvious correlation between [M/H] and MP or orbital properties (a, e)

How about the kinematics of the (sub-)sample?


Stellar kinematicsStellar kinematics

1. Generally characterised as Schwarzschild velocity ellipsoid, with Gaussian dispersions in cardinal directions: U, V, W

2. Dispersions (U,, V,, W,, tot), are expected to increase with age: tot 1/3 (diffusion theory)

3. A composite population – use probability plots

Cumulative velocity distribution as a function of inverse probability:Gaussian straight line2 Gaussians 3 line segments


Host star kinematicsHost star kinematics field hostsfield hostsU -9.6 -4.0U -9.6 -4.0V -20.2 -25.5V -20.2 -25.5W -7.6 -20.4W -7.6 -20.4UU 38.8 37.7 38.8 37.7VV 31.0 22.9 31.0 22.9WW 17.7 20.4 17.7 20.4TotTot 52.7 48.6 52.7 48.6

Planetary hosts are Planetary hosts are representative of representative of the local field starsthe local field stars


Kinematics & samplingKinematics & sampling

Even though the hosts reside in the Even though the hosts reside in the Solar Neighbourhood Solar Neighbourhood nownow, they , they are likely drawn from Rare likely drawn from R00±1.5 kpc±1.5 kpc


And the thick diskAnd the thick disk

All three thick-disk All three thick-disk candidates have candidates have significant motions significant motions w.r.t. the Sun – w.r.t. the Sun – notably HD 37124 notably HD 37124 & HD 114762& HD 114762


Kinematics and planetary Kinematics and planetary propertiesproperties

No obvious No obvious correlations between correlations between space motions and space motions and planetary planetary characteristicscharacteristics(cf. Santos et al, (cf. Santos et al, 2003).2003).


Corotation and planetsCorotation and planets

Is the Sun’s near-LSR Is the Sun’s near-LSR velocity important? velocity important? (the issue of long-(the issue of long-term habitability)term habitability) apparently not, at apparently not, at least for planet least for planet formationformation


Covering the GalaxyCovering the Galaxy

Planetary formation apparently Planetary formation apparently depends only on stellar depends only on stellar metallicity.metallicity.Most planets are likely to be Most planets are likely to be associated with thin disk starsassociated with thin disk stars Predicting the overall Predicting the overall frequency throughout the frequency throughout the Galaxy requires:Galaxy requires:

1. Thin disk density distribution:Thin disk density distribution: (R) =(R) = 0 0 ee-(R-R0)/h-(R-R0)/h e e-z/z0-z/z0 where h ~ 2500 pc, z0 ~ 300 where h ~ 2500 pc, z0 ~ 300

pcpc2.2. The abundance distribution as f(R) : The abundance distribution as f(R) : both <[m/H]> and N ([m/H])both <[m/H]> and N ([m/H])


Radial abundance Radial abundance gradientsgradients

Data for HII regions (Shaver et al, 1983) and Cepheids Data for HII regions (Shaver et al, 1983) and Cepheids (Andrievsky et al, 2002) suggest a broad plateau in <[m/H]> (Andrievsky et al, 2002) suggest a broad plateau in <[m/H]> from 6-10 kpc; mild decline at >10 kpc; steep rise at R< 6 kpc. from 6-10 kpc; mild decline at >10 kpc; steep rise at R< 6 kpc. These are all relatively young tracers – what about the older These are all relatively young tracers – what about the older stars?stars?


Abundance distributionsAbundance distributions

How metal-rich is the underlying How metal-rich is the underlying older population in the inner older population in the inner disk?disk?

SN – SN – HaywoodHaywood(2002)(2002)

Bulge Bulge Ferreras, Ferreras, Wyse & Wyse & Silk (2003)Silk (2003)


Counting planetsCounting planetsAs a partial estimate:As a partial estimate:

• limit analysis to 6 < R < 10 kpclimit analysis to 6 < R < 10 kpc

• assume the Solar Neighbourhood metallicity distributionassume the Solar Neighbourhood metallicity distribution

• adopt adopt (R) =(R) = 0 0 ee-(R-R0)/h-(R-R0)/h e e-z/z0-z/z0, where h ~ 2500 pc, z0 ~ , where h ~ 2500 pc, z0 ~ 300 pc300 pc

• use the nearby-star luminosity function to set the use the nearby-star luminosity function to set the density density normalisation of solar-type starsnormalisation of solar-type stars 4 < M4 < MVV < 6 < 6 4.4 x 10 4.4 x 10-3-3 stars pc stars pc-3-3 2.74 stars pc 2.74 stars pc-2-2 • assign 90% to disk; 10% to thick diskassign 90% to disk; 10% to thick disk


Planets in the Solar RingPlanets in the Solar RingDensity wins over area Density wins over area N NPP decreases with R decreases with R

Numbers compensate Numbers compensate for frequency for frequency solar-metallicity solar-metallicity systems are almost as systems are almost as common as metal-rich common as metal-rich systemssystems

In total, expectIn total, expect NNPP ~ 3.5 x 10 ~ 3.5 x 1077 (6%) (6%) for 6 < R < 10 kpcfor 6 < R < 10 kpc a < 4 AU, a < 4 AU, M M > ~1> ~1MMJJ


Are there carbon planets Are there carbon planets in the inner Galaxy?in the inner Galaxy?

Hypothesis: if C/O > 1, CO binds Hypothesis: if C/O > 1, CO binds [O], preventing silicate [O], preventing silicate formation formation Carbides dominate to give C-Carbides dominate to give C-rich planet (Kuchner & Seagar)rich planet (Kuchner & Seagar)

C originates in intermediate-C originates in intermediate-mass stars (AGB) and high mass mass stars (AGB) and high mass WC stars (~equal proportions)WC stars (~equal proportions) C/O increases with [Fe/H] C/O increases with [Fe/H] (time)(time)

[C] = 8.39, [O] = 8.66[C] = 8.39, [O] = 8.66 Require [C/O] ~ +0.3, Require [C/O] ~ +0.3, suggesting [Fe/H] > 0.4suggesting [Fe/H] > 0.4

Gustafsson et al, 1999 – Gustafsson et al, 1999 – fine analyses of nearby fine analyses of nearby FG starsFG stars


SummarySummary

1.1. Planetary host stars are remarkably Planetary host stars are remarkably unremarkable (once one allows for the unremarkable (once one allows for the preference for high [m/H])preference for high [m/H])

2.2. Several of the known systems are probably Several of the known systems are probably members of the thick diskmembers of the thick disk

3.3. Integrating planetary frequency across the Integrating planetary frequency across the Galaxy is currently limited by our knowledge Galaxy is currently limited by our knowledge of the abundance distribution in the inner and of the abundance distribution in the inner and outer Galaxy – but there are likely >3.5 x 10outer Galaxy – but there are likely >3.5 x 1077 “RV-detectable” systems in the 6 to 10 kpc “RV-detectable” systems in the 6 to 10 kpc Solar Ring.Solar Ring.


Never mind the planets, Never mind the planets, where’s the food?where’s the food?

extrasolar planets: a galactic perspective i. neill reid stsci

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