Planet formation and stellar multiplicity

Insights from recent surveysGaspard Duchêne(UC Berkeley, Obs. Grenoble)

© N

ASA

/JPL/

Calt

ech

Planets in multiple systems?

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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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