Download Santos: 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...
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
From Santos et al. (2004)
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)
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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?
Johnson et al. (2010)
Santos et al. (2004); Udry & Santos (2007)
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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)
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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)
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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
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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
Missing metal-rich stars?
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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!
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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)
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New planet radius domains explored
Kepler: no correlation found for Neptune-sized planets
(Buchhave et al. 2012)
R<4REarth
R>4REarth
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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.
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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.
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A correlation after all?
(Wang+ 2013)
A correlation after all?
(Wang+ 2013)
Further evidence?
Kepler: evidence for three
different regimes?
(Buchhave et al. 2014)
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Further evidence?
Kepler: evidence for three
different regimes?
And a transition radius that
depends on orbital period?
(Buchhave et al. 2014)
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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
HARPS planets (Mayor et al. 2011) + Kepler planets (from Buchhave et al. 2012)
Abundances from high resolution spectra (Adibekyan et al. 2012)
From 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)
From 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)
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
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?
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