gaspard duchêne (uc berkeley, obs. grenoble) © nasa/jpl/caltech
TRANSCRIPT
Planet formation and stellar multiplicity
Insights from recent surveysGaspard Duchêne(UC Berkeley, Obs. Grenoble)
© N
ASA
/JPL/
Calt
ech
Planets in multiple systems?
© LucasFilm Ltd.
They must exist!
Planets in multiple systems! One of the pulsar planets is
circumbinary First planets in Main Sequence binary
systems reported as early as 1997 (Butler et al.)
And now MS circumbinary planets…
© NASA© Greg Bacon – STScI/NASA
PSR 1620-26 Kepler 16
Some open questions
Do planets form in multiple systems? YES ! In a remarkable diversity of systems!
Does the influence of a stellar companion
affect the planet properties at all?
How different are the initial conditions for
planet formation in multiple systems?
Let’s summarize the empirical
evidence…
Schematics of the problem…
The early phases of planet formation
occur in a circumstellar disk within a
few Myr What is the influence of a stellar
companion? Dynamical truncation, but then what?
Stellar multiplicity
~50% of solar-type stars have a stellar
companion Most companions are on close orbits
(<100 AU) Even higher frequency
for PMS objects! Far from a
marginal phenomenon !Raghavan et al. (2010)
Protoplanetary disks
Planet-forming
disks have sizes ≥
100 AU Only a small
fraction of the
mass resides within
~10 AU, where
planets presumably
form
Andrews & Williams (2007)
Importance of outer mass reservoir thatcan be most affected by a companion
SMA
Outline
The basics of stellar multiplicity and
disks Multiple stars and …
Protoplanetary disks (initial conditions)
Debris disks (early stages)
Planetary systems (mature systems)
Back to the big picture
Primordial disks in binaries Both stars have a disk
in most cases Disks around primaries
are more massive
tend to survive longer (?)
Primaries offer better grounds to form planets
Harris et al. (2012)
SMA
Primordial disks in binaries Disks are much rarer in tight binaries
(≤ 40 AU) than in wide ones or
around single stars Clearing during formation?
Fast dissipation? No replenishment?
Remaining disks are
long-lived (~ 5 Myr)
Kraus et al. (2012)
Taurus-Auriga (~1-
3Myr)
Spitzer
Total disk mass
Limited mass reservoir in tight binaries Or are compact disks massive and
optically thick? No strong dependence on mass ratio
Harris et al.
(2012)
Circumbinary disks
Taurus
SMA
Inner regions properties
When present in binary systems, disks have similar properties in the innermost region Only the disk surface within < 1AU of the
star
Pascucci et al. (2008)
Silicate feature
NIR colors
Cieza et al. (2009)
disk
larger grain size
Spitzer
Missing pieces in the picture…
The presumed planet-forming region (3-20AU) is not probed by either (sub)mm or NIR Need to probe the FIR!
What about the gas? 99% of the mass…
10μm
1.3mm
70μm
~250 young stars,incl. 106 in Taurus
PI: Bill Dent
Pinte et al. (2008)
IM Lup, ~1M, Rout=400AU
Spitzer
SMA
The planet-forming region
Neither the FIR continuum nor the [OI]63 line (main cooling line) depend on separation
No influence of stellar companions
C. Howard et al. (in prep)
circumbinary Taurus
submm
FIR cont[OI]63 line
Herschel
Protoplanetary disks: summary
Disks in primaries are more auspicious
to planet formation than those of
secondaries Outer disk regions are severely
depleted in tight binaries (separation
< ~100 AU) Lower total disk mass? Shorter lifetime?
Planet-forming region is apparently
unaffected by the presence of a
companion
Outline
The basics of stellar multiplicity and
disks Multiple stars and …
Protoplanetary disks (initial conditions)
Debris disks (early stages)
Planetary systems (mature systems)
Back to the big picture
Debris disks in binaries
Binaries among known debris disks: 15-25% Mannings & Barlow (1998), Plavchan et al. (2009)
But binary surveys incomplete, especially for A stars
“If anything, stars in binary systems show less excess emission” (Rieke et al. 2005)
Detection rate in binaries ~ 33%, slightly higher than among singles (Trilling et al. 2007)
Situation needs clarification…
Debris disks: separation trend
Known debris disks have few companions in the 1-100 AU range (bias?) © Tim Pyle – SSC/NASA
Trilling et al. (2006)Rodriguez & Zuckerman (2012)
113 AFGK stars 63 AF stars
IRAS / ISO
Spitzer
Debris disks: the Herschel view
An unbiased volume-limited survey is needed to draw a robust statistical picture
➜ DEBRIS survey (PI: Brenda Matthews) ~450 targets, A through M stars (~90 per
Sp.T. class) Unbiased sample Uniform observing strategy
Debris disks: the Herschel view To complement the Herschel
observations, we are gathering a catalog of stellar companions Literature/catalog searches Lick Adaptive Optics survey (200+
targets)
D. Rodriguezet al. (in prep)
Debris disks: the Herschel view Debris disks are less frequent in
binaries 13.7% vs 22.6 % for the whole sample
Companions in the 1-1000 AU are particularly disruptive (true for all spectral types)
D. Rodriguezet al. (in prep)
Herschel
Outline
The basics of stellar multiplicity and
disks Multiple stars and …
Protoplanetary disks (initial conditions)
Debris disks (early stages)
Planetary systems (mature systems)
Back to the big picture
Exoplanets in binaries
Most planets are found around primaries Exceptions: 16 Cyg B, HD 178911 B but few searches around (lower mass)
companions A handful of planets in triple systems
Usually (A-b) – (B-C) Extreme case: γ Cep
Planet: a=2 AU, e=0.2 Comp: a=20 AU, e=0.4Raghavan et al. (2006)
planet companion
Exoplanets: multiplicity
~33% of known exoplanet hosts are
binaries Slightly lower rate than among singles But severe negative selection bias!
Possible deficit of planets
if separation ≤ 100 AU Better statistics w/ Kepler?Eggenberger et al. (2009)
Exoplanets: finer dependencies
Early studies suggested a peculiar trend Close-in planets in binaries are more
massive No trend in larger sample (nor with
e)However …
Zucker & Mazeh (2002)
From Exoplanet Encyclopedia and Mugrauer & Neuhauser (2009)
Exoplanets: finer dependencies
Planets in wide systems are indistinguishable from those around single stars
Planets in tight binaries always have high mass No influence of other orbital elements (P, e)
Duchêne (2010)
Outline
The basics of stellar multiplicity and
disks Multiple stars and …
Protoplanetary disks (initial conditions)
Debris disks (early stages)
Planetary systems (mature systems)
Back to the big picture
Planet formation in binaries
Wide binaries (separations beyond ~50-100 AU) have little influence on the overall process Almost half of all solar-type binaries! Despite truncation, only the inner 10-30 AU
matter, provided enough mass is accumulated early on
Planet formation in binaries
Truncation by tighter binaries is severe, but does not prevent planet formation altogether Many disks disappear early on (or never
form?) Few debris disks are found Planets are always of high mass
A different path to form planets?
??
Planet formation in binaries
Planets are common in tight binaries (< 1-2 AU) Protoplanetary disks offer sound initial
conditions
Debris disks show that planetesimals formed from these disks
An “almost normal” formation process
Planet formation in binaries
Normalprocess
Quasi-normalprocess
A different process, affecting ~25% of all solar-type stars (disk fragmentation?)
Raghavan et al. (2010)
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