Observing binaries with GAIA: large gains after much effort'''

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Observing binaries with GAIA large gains after
much effort...

• Staffan Söderhjelm
• Lund Observatory

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Pros and cons...

• Millions of binaries of all kinds
• Complete statistics near sun
• Partial statistics over large parts of the Galaxy
• Orbits and masses

• Increased size of sampling windows
• Greatly complicated reductions
• Orbital p.m. bias in the galactic dynamics
• Photometric bias from unresolved binaries

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Most stars are binary/multipleMost stars look
single
because

• a-distribution is very wide (10-2 105 a.u.)
• q-distribution peaks at low q (Msec/Mpr ltlt 1)
• evolution makes a lot of wds

Observationally, a typical star has a
companion, but with dm gt 5-10. It will be easily
discovered by GAIA if the period is less than 30
years, but not if it is above 100 years.
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Census of binaries

• Huge numbers (107-8 resolved, 107 astrometric,
  106-7 eclipsing, 106 spectroscopic), but still
  most undetected...
• Non-uniform sampling at different distances
  (resolved/unresolved, magnitude-effects)
• Possibilities to check statistics in different
  parts of the Galaxy, not only solar neighborhood

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Orbit determinations

• (1-10 yr) resolved bin gt indiv. masses
• astrometric bin gt m23/(m1m2)2 (1-ß/µ)3
  (incl. extrasolar planets and BD, ß0)
• eclipsing bin gt low-prec masses and radii
• SB1astrometric gt m23/(m1m2)2 , (ß/µ)
• SB1ecl gt m23/(m1m2)2 , ß
• SB2ecl gt masses and radii

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Common problemdetermination of periods

• few epochs, aliasing
• astrometric signal very non-explicit
  (RV and/or photometry simpler)
• too many objects for manual intervention

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Design problems for resolved binaries

• Binaries need larger sampling windows gt Conflict
  between more faint singles or better data for
  secondaries
• Optimal strategy needs to be simple but not
  simplistic...
• Realistic Galaxy models needed

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Design problems for unresolved binaries

• Systematic astrometry errors due to mean color
  PSF instead of correct individual ones?
• MBP filter optimization needs to consider
  binaries
• RV/MBP pixels much larger gt worse overlap
• Influence of variability (VIM-doubles)
• Realistic Galaxy models needed

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Some critical issues 2002-2004

• Effects of the GAIA-2 design!
• Detection algortithm
• Sampling windows/obs strategy
• Spatial resolution for MBP/Spectro
• Binarity effects in the MBP filter selections
• SB-observing with different Spectro designs
• Galaxy model with realistic doubles
• Binaries/multiples in reduction prototype
• Database principles (what is a multiple system?)

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Development of reduction methods

• Resolved doubles (how to get a priori positions?)
• Period-finding (for resolved, astrometric,
  eclipsing binaries)
• Resolved binary orbits (mass-determination)
• Astrometric binary orbits (with or without RV)
• Extrasolar planet orbits
• Eclipsing binaries/planetary transits
• Plus a never-ending list of special cases...

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Scientific issues(guide to priorities)

• Binary statistics (age/place resolved)
• Binary origin and evolution
• Individual stellar parameters
• Extrasolar planets (masses and orbits)
• ....