Download Mass Determinations in Binary Systems

Mass Determinations in Binary
Systems
• Complications
– Inclination: orbital plane not
necessarily perpendicular to line of
sight.
– Projection of ellipse is another
ellipse with different eccentricity.
Inclination angle can be inferred by
such that projected foci are
consistent with actual foci.
Spectroscopic Binaries
• Can’t resolve starts spatially
but can observe Doppler
shift of
emission/asbsorption lines.
• Use Doppler shift to determine projected velocities
• For small eccentricities:
Extrasolar Planets
• Treat like single-line spectroscopic binary
– suppose you can’t detect the spectra of the faint
star (or planet) in a binary system, so vr2 isn’t
measurable. Then you can’t determine both
masses, but if you know one you can determine
the other.
– For extrasolar planets, the mass of the star is
known from is spectral type
Doppler Shift of Stellar Wobbles
• Motion of Sun due to Planets:
Kepler NASA mission (Occultations)