Orbits of Double Stars from Long Baseline Optical Interferometry
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**Session 86 -- Double Stars**
*Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)*

## [86.04] Orbits of Double Stars from Long Baseline Optical Interferometry

*C.A.Hummel, J.T.Armstrong (USRA)*
The spectroscopic binary observing program of the Mark III Optical
Interferometer has produced six published orbits and twenty preliminary
orbits. The mean precision is 0.3\% for measurements of $\sin i$ and
0.7\% for measurements of the semimajor axis $a$. These orbits represent
more than half of the systems with detected nightly visibility variations
in excess of about 20\%, corresponding to a pair of unresolved components
with a magnitude difference of not more than 2.4 magnitudes. By the same
criterion, we detected indications of multiplicity in about half of the
stars we had selected from catalogs of spectroscopic binaries with predicted
major axes between 3 mas and 40 mas, $m_{\rm V} < 5$, $\delta > -10^\circ$,
and for which we had obtained a sufficient amount of data.

We describe our data analysis, which features direct
fitting of the orbital elements and component parameters to the measured
visibilities, as well as our uncertainty analysis based on Monte Carlo
simulations.

We present results on some of the binaries, notably a very high precision
orbit of Capella with the component diameters determined, and sub-10-mas
angular scale orbits of $\beta$ Aurigae, $\pi$ Andromedae, $\theta$ Aquilae,
$\beta$ and $\delta$ Trianguli. We discuss some of the results in terms of
stellar evolution theory.

**Friday
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