Download Observing binaries with Gaia

Observing binaries with GAIA:
large gains after much effort...
Staffan Söderhjelm
Lund Observatory
Pros and cons...
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• 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
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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)
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Binary statistics (age/place resolved)
Binary origin and evolution
Individual stellar parameters
Extrasolar planets (masses and orbits)
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