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. 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

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

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Observing binaries with gaia large gains after much effort

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

Pros and cons...

+


Most stars are binary multiple most stars look single

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 << 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

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


Orbit determinations

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

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

‘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

‘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

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

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

Scientific issues(guide to priorities)

  • Binary statistics (age/place resolved)

  • Binary origin and evolution

  • Individual stellar parameters

  • Extrasolar planets (masses and orbits)

  • + ....


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