On the relation between stars and their planets

On the relation between stars and their planets Nuno C. Santos Centro de Astrofísica, Universidade do Porto Instituto de Astrofísica e Ciências do Espaço

Why we stellar parameters are important in exoplanets Stellar properties may influence the capacity to detect planets (e.g. spectral type, activity,...) Stellar parameters are crucial for the determination of planet properties Planet mass, radius, mean density => stellar mass and radius System s age => stellar age Habitability => stellar irradiation (temperature, luminosity, activity,...) Observed correlations between planet and stellar properties are observed (clues to formation/evolution): Stellar properties: abundances, luminosity, mass, irradiation, activity,... Planet properties: internal structure (metallicity), radius, orbital parameters...

Outline of the talk The metallicity-giant planet connection FGK stars: the functional form M dwarfs, giant stars Metallicity-planet connection for low-mass/radius planets HARPS and Kepler results The relevance of the abundances of different elements I. The role of alpha elements II. Condensation temperature trends Lithium and planets Metallicity and planet architecture Some problems in stellar parameters/abundances

Giant planets and metallicity

The metallicity-giant planet correlation 10 years ago Strong support towards intrinsic origin (e.g. Santos et al. 2004, Fischer & Valenti 2005) Clues for planet formation models Core accretion model: metallicity dependence predicted (e.g. Mordasini et al. 2012) Disk instability models: less clear if metallicity should play a role (e.g. Boss et al. 2002) From Santos et al. (2004) 6

The Functional Form for giant planets: the discussion Contradictory results exist: different formation processes at different metallicity? A flat tail for low metallicities? A simple power-law? Santos et al. (2004); Udry & Santos (2007) Johnson et al. (2010) 7

Results from the analysis of the HARPS sample Recent statistical analysis: both solutions have equal significance! Mortier et al. (2012)

Results from the analysis of the HARPS sample Recent statistical analysis: both solutions have equal significance! No significant difference! Mortier et al. (2012)

Does it all fit? Evidence for very early planet formation The star is much likely solar metallicity or lower (Santos et al. 2008; D Orazi et al. 2009; Biazzo et al. 2012) HL Tau - ESO-PR

M-dwarfs: metallicity and planets M-dwarfs: [Fe/H]-giant planet correlation also seems to be present (Neves et al. 2013) 11

Giant stars: to be or not to be? Giant stars with giant planets: no metallicity correlation? Evidence for planet engulfment? (Pasquini et al. 2007) A mass effect? (Ghezzi et al. 2010) A possible spectroscopic analysis issue? (Hekker & Melendez 2007, Santos et al. 2009) Or maybe there is a correlation after all? (A. Quirrenbach, priv. comm.) (Mortier et al. 2013) 12

A selection bias? (Mortier et al. 2013) Field giant star sample from (giant) planet search programs (Takeda et al. 2008 + da Silva et al. 2006 + Zielinski et al. 2012) Planet-host giants B-V cuts in sample 13

Low-mass/radius planets and metallicity

What did HARPS, Kepler, et al. provide? An increase in the numbers... but more importantly: a new parameter space, low mass/ radius planets! 16

New planet mass domains explored HARPS: no correlation found for Neptune-mass planets (e.g. Udry et al. 2007; Sousa et al. 2011; Mayor et al. 2011) Jovian companions Neptunes and Super-Earths From Sousa et al. (2011) - see also Mayor et al. (2011) 17

New planet radius domains explored Kepler: no correlation found for Neptune-sized planets (Buchhave et al. 2012) R<4REarth R>4REarth 18

The metallicity-planet-mass correlation Results in line with planet synthesis models based on core-accretion (e.g. Mordasini et al. 2012) From Mordasini et al. (2012) From Mortier et al. 19

The metallicity-planet-mass correlation Earths should be very common!!! (in particular around low metallicity stars) Lots of Earths From Mordasini et al. (2012) From Mortier et al. 20

A correlation after all? (Wang+ 2013)

Further evidence? Kepler: evidence for three different regimes? (Buchhave et al. 2014) 23

Further evidence? Kepler: evidence for three different regimes? And a transition radius that depends on orbital period? (Buchhave et al. 2014) 24

A transition from solid to icy worlds? Transition at radius ~1.5 REarth (or ~3.5 MEarth)

Exploring other elements...

What about other elements? Search for clues in other elemental abundances How does the frequency of planets behave with different elemental abundances (alpha-elements, iron peak)? Are any elements specially important for planet formation? (e.g. C, O, volatile/refractory ratios,...) Specially relevant for metal-poor systems where a bit more of grains can make the difference?

I. The role of alpha elements in the metal-poor regime HARPS planets (Mayor et al. 2011) + Kepler planets (from Buchhave et al. 2012) Abundances from high resolution spectra (Adibekyan et al. 2012)

I. The role of alpha elements in the metal-poor regime HARPS planets (Mayor et al. 2011) + Kepler planets (from Buchhave et al. 2012) Abundances from high resolution spectra (Adibekyan et al. 2012) Thick disk Thin disk From Adibekyan et al. (2012)

I. The role of alpha elements in the metal-poor regime Conclusion 1: higher frequency of planets if star is rich in alpha element Ti Conclusion 2: metals critical in metal-poor stars even for low mass planet formation Planet frequency: 12.3+-4.1% Planet frequency: 2.2+-1.3% From Adibekyan et al. (2012)

II. Condensation temperature trends and planets Observation: condensation temperature trends in the Sun show that our star is poor in refractory elements when compared to other solar analogs (e.g. Melendez et al. 2009) Interpretation: refractories remained in rocky planets (Ramirez et al. 2009, 2010)

II. Condensation temperature trends and planets No evidence for this interpretation when comparing planet-hosts with single stars (e.g. Gonzalez-Hernandez et al. 2010)

II. Condensation temperature trends and planets Really an imprint of planet formation? OR: related to the galactic origin of the star?

II. Condensation temperature trends and planets Really an imprint of planet formation? OR: related to the galactic origin of the star? Relation between Tc slope and age of the star!!! Solar analogs Same trend is seen with stellar galactocentric radius Solar twins From Adibekyan et al. (2014)

II. Condensation temperature trends and planets Conclusion: Galactic birth place and age are determinant to establish Tc slopes (expected from models - Lemasle et al. 2008) Older stars are more depleted in refractory elements From Adibekyan et al. (2014)

II. Condensation temperature trends and planets Conclusion: Galactic birth place and age are determinant to establish Tc slopes (expected from models - Lemasle et al. 2008) Tc slope trends: no direct relation with presence of planets Older stars are more depleted in refractory elements Most planet hosts (including Sun) are old From Adibekyan et al. (2014)

II. Condensation temperature trends and planets Old solar analog that shows similar pattern as the Sun, contrarily to younger solar analogs! (e.g. Monroe et al. 2013; Melendez et al. 2014)

Light elements in stars with planets: Lithium

Lithium in solar-like field stars Li Lithium is a tracer of internal mixing is stars Teff

Lithium in planet hosts: signature of stronger depletion e.g. Israelian et al. (2009), Delgado-Mena et al. (2014)

Lithium in planet hosts: signature of depletion A long debate...

Lithium in planet hosts: signature of depletion The most recent approach (Figueira et al. 2014): Use a multivariate approach where the Li abundance is expressed as a function of the different parameters, including a moderator variable M (1=planet host; 0=no planet)

How to explain higher depletion? Star-disc interaction during PMS: planet hosts become slow rotators and develop a high degree of differential rotation between the radiative core and the convective envelope that induces mixing (Bouvier 2008) Episodic accretion of planetary material may produce mixing of material and thus Li destruction (Baraffe & Chabrier, 2010; Théado &Vauclair, 2011) Angular momentum transfer related to planet migration (Castro et al. 2009)

Metallicity and planet architecture...

I. Metallicity in the mass-period diagram Kepler data: lack of short period (P<5 days) planets with R<4REarth around low-[fe/h] stars From Beaugé & Nesvorny (2013) No red points here

I. Metallicity in the mass-period diagram Radial velocity planets (brighter stars => precise parameters and abundances) From Adibekyan et al. (2013)

I. Metallicity in the mass-period diagram Radial velocity planets: no [Fe/H]- rich stars with long period planets Beaugé & Nesvorny (2013)? From Adibekyan et al. (2013)

I. Metallicity in the mass-period diagram Hints about migration? Planets form further out in metal-poor systems? Adibekyan et al. (2013) From Adibekyan et al. (2013)

II. Planets, metallicity, and eccentricity Circular Eccentric Dawson & Murray-Clay (2013) Hints for higher eccentricity for planets orbiting higher [Fe/H] stars

II. Planets, metallicity, and eccentricity Circular Eccentric Dawson & Murray-Clay (2013) Effect of planet-planet scattering? Disk interaction depends on [Fe/H]? (Tsang et al. 2014)

A word of caution...

A word of caution Different groups can obtain very different stellar parameters (e.g. Smiljanic et al. 2014)

A word of caution Same for other elements (e.g. Hinkel et al., in prep.)

A word of caution Bottom line: Spectroscopy is not easy! We can often assure precision but accuracy is much more difficult to guarantee!

SWEET-Cat (http://www.astro.up.pt/resources/sweet-cat) (Santos+ 2013)

Conclusions Chemical abundances strongly related with planet frequency True in all planet mass regimes M-dwarfs and giant stars Still a lot to be done (need numbers and unbiased samples/analysis) In metal-poor regime Chemical content is still critical for formation of low mass planets Tc slope trends Age/Galactic formation region effect: not connected with rocky planet formation Lithium and planets: evidence for extra depletion Metallicity also influences planet architecture

Thank you! Questions? 61