Gaspard Duchêne (UC Berkeley, Obs. Grenoble) © NASA/JPL/Caltech

© LucasFilm Ltd. They must exist!

 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 Kepler 16

 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…

 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?

 ~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)

 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 that can be most affected by a companion SMA

 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

 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

 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

 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

 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

 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 , R out =400AU Spitzer SMA

 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) circumbinaryTaurus submm FIR cont [OI]63 line Herschel

 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

 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

 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…

 Known debris disks have few companions in the AU range (bias?) © Tim Pyle – SSC/NASA Trilling et al. (2006) Rodriguez & Zuckerman (2012) 113 AFGK stars 63 AF stars IRAS / ISO Spitzer

 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

 To complement the Herschel observations, we are gathering a catalog of stellar companions  Literature/catalog searches  Lick Adaptive Optics survey (200+ targets) D. Rodriguez et al. (in prep)

 Debris disks are less frequent in binaries  13.7% vs 22.6 % for the whole sample  Companions in the AU are particularly disruptive (true for all spectral types) D. Rodriguez et al. (in prep) Herschel

 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

 Most planets are found around primaries  Exceptions: 16 Cyg B, HD 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=0.4 Raghavan et al. (2006) planetcompanion

 ~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)

 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)

 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)

 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

 Wide binaries (separations beyond ~ AU) have little influence on the overall process  Almost half of all solar-type binaries!  Despite truncation, only the inner AU matter, provided enough mass is accumulated early on

 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? ??

 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

Normal process Quasi-normal process A different process, affecting ~25% of all solar-type stars (disk fragmentation?) Raghavan et al. (2010) © NASA/JPL/Caltech © LucasFilm Ltd. © Tim Jones – McDonald Obs.