Gaia Unresolved
Can we build a data-driven model of the binary fraction and binary mass ratio distribution for stars? Use the unresolved binaries from Gaia to infer the fraction and mass ratio distribution for the field.
How
- detect as displacements from the stellar main sequence in the Color vs Absolute Magnitude diagram (CMD)
- use stellar models to convert CMD (B-V, M_V) to mass & mass ratio (M_1, q)
- unless @ixkael, @andersdot, and @davidwhogg think it can be done w/o stellar models...
- model fraction of binary stars (f) and mass ratio distribution (q) as function of primary mass (M_1)
- try to do it independent of star formation history (SFH)!
- can we do it independent of the initial mass function (IMF)?
My thinking is calibrated on this figure from Hurley & Tout (1998)
Assumptions
- Stars are either singles or doubles
- all stars are main sequence (dwarfs)
Thoughts
- Binaries with mass ratios closer to q=1 are of course easier to detect
- need to model as fraction of binaries and single stars at each mass
- We should see the equal-mass (parallel) main sequence in Gaia field data, as is seen in many Open Clusters at ~0.75 mag brighter
- Cheesy: Can we find any sign of a THIRD main sequence from equal-mass tripples (~1.2 mag brigher)?
AstroHackWeek Results
1) I can make this figure with isochrones, and it overlaps Gaia data nicely! 2) there might be some evidence for triple stars above the double-star main sequence 3) doing some basic plots of "caustics" that result from distributions of triple-star masses...