An ancient extrasolar system with fivesub-Earth-size planets

Tiago Campante1,2

1University of Birmingham, UK

2Stellar Astrophysics Centre (SAC), Aarhus University, Denmark

September 18, 2014

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Introducing KOI-3158

also KIC 6278762,HIP 94931

spectral type K0V

over 0.5 arcsec yr−1

V = 8.86

d = 36 pc

iron-poor andoverabundant in αelements (e.g., Siand Ti)

Atmospheric parameters

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A member of the thick disk (I)

thick disk

thin disk

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A member of the thick disk (II)

Toomre diagram

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Possible extragalactic origin?

member of the Arcturusstream

named after Arcturus(brightest star in northerncelestial hemisphere)

these stars travel 2 kpcabove Galactic plane

extragalactic originvs. dynamical origin withinGalaxy

artist’s conception

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Hierarchical triple system

fainter companion at1.8 arcsec

high-resolutionimaging withRobo-AO

3.94 % dilution

the two componentsare co-moving

secondary comprisestwo M dwarfs!

two M dwarfs!

KOI-3158

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Asteroseismic analysis (I)

short cadence: Q4.2, Q6,Q15–17

record-breaking ∆ν at180 µHz

stellar properties fromgrid-based modeling

1.9 % relative precisionon R and 1.1 % on 〈ρ〉

Stellar properties

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Asteroseismic analysis (II)

detailed frequencymodeling

GARSTEC, ASTEC,YREC, MESA, and AMPcodes used

11.2 billion years old!

9 % precision on ageestimate

oldest known system ofterrestrial-size planets

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Transit analysis

4 years oflong-cadence data

five-planet transitmodel

affine-invariantMCMC algorithm

took into accountdilution

KOI-3158.01

KOI-3158.02

KOI-3158.03

KOI-3158.04

KOI-3158.05

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A system of terrestrial-size planets

KOI-3158.01 isMercury-sized

intermediate planets areMars-sized

KOI-3158.05 smaller thanVenus

from the mini-Neptunesaround Kapteyn’s star andKepler-10’s super-Earths tothe terrestrial-size regime

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Highly-compact system

orbital periods under 10days

. . . or within 0.08 AU

period ratios close tostrong 5: 4, 4 : 3, 5 : 4,and 5: 4 first-orderMMRs

system fits within orbitof Kepler-11’s innermostplanet

compact systems makeup ∼1 % of Keplercandidate hosts

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Dynamical evolution

proximity to strong resonances points to dynamical evolution

convergent inward migration is likely mechanism

tides then push planets wide of exact commensurability

will make an interesting case study!

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System validation

only plausible FP of 4planets + 1 backgroundEB rejected at 99.9 %level

no background stars inDSS archival data

non-randomness ofobserved multi-resonantchain

dynamical instability ifplanets were to orbitM-dwarf companion

DSS POSS-I (epoch 1945-58) DSS POSS-II (epoch 1984-99)

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Implications (I)

giant-planet hosts:metal-rich

small-planet hosts: morediverse composition

⇒ terrestrial-size planetsmay have started to formearlier

(sub-)Earth-sizeplanets have formedthroughout most ofUniverse’s history

ancient life in theGalaxy?

Buchhave et al. (2012)

blue: small planets (<4 R⊕)

red: giant planets (>4 R⊕)

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Implications (II)

α elements critical forplanet formation iniron-poor environments

thick-disk starsoverabundant in αelements inlow-metallicity regime

⇒ thick-disk (and high-αhalo) stars were likelyhosts to first Galacticplanets

ancient systemsaround KOI-3158 andKepler-10 helppinpoint beginning ofera of planet formation

Adibekyan et al. (2012)

black line: exoplanet-host trendgreen line: non-host trend

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Acknowledgments

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