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Observing binaries with GAIA: large gains after much effort... Staffan Söderhjelm Lund Observatory 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 Most stars are binary/multiple Most stars look single because -2 5 • a-distribution is very wide (10 – 10 a.u.) • q-distribution peaks at low q (Msec/Mpr << 1) • evolution makes a lot of wd:s Observationally, a ‘typical’ star has a companion, but with dm > 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. Census of binaries 7-8 7 • Huge numbers (10 resolved, 10 astrometric, 6-7 6 10 eclipsing, 10 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 Orbit determinations • (1-10 yr) resolved bin => indiv. masses • astrometric bin => m23/(m1+m2)2 (1-β/μ)3 (incl. extrasolar planets and BD, β=0) • eclipsing bin => low-prec masses and radii • SB1+astrometric => m23/(m1+m2)2 , (β/μ) • SB1+ecl => m23/(m1+m2)2 , β • SB2+ecl => masses and radii Common problem: determination of periods • few epochs, aliasing • astrometric signal very non-explicit (RV and/or photometry simpler) • too many objects for ‘manual’ intervention ‘Design’ problems for resolved binaries • Binaries need larger sampling windows => Conflict between ‘more faint singles’ or ‘better data for secondaries’ • ‘Optimal’ strategy needs to be simple but not simplistic... • Realistic Galaxy models needed ‘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 => worse overlap • Influence of variability (‘VIM’-doubles) • Realistic Galaxy models needed 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?) 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’... Scientific issues (guide to priorities) • • • • • Binary statistics (age/place resolved) Binary origin and evolution Individual stellar parameters Extrasolar planets (masses and orbits) + ....