Dynamical parallax
Distance to visual binaries via orbital and brightness data.
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Dynamical parallax is a method for estimating the distance to a visual binary star system. It is notable because it allows astronomers to derive a distance without relying on direct trigonometric parallax measurements, using instead the observed orbital motion and brightness of the stars.
Quick Facts
- Accuracy
- within 5%
- Method basis
- Newton's generalisation of Kepler's Third Law and the mass–luminosity relation
- Iterative process
- repeated many times
- Initial mass estimate
- usually as the mass of the Sun
Facts from the source article.
Background
The technique begins by observing the angular semi-major axis of the binary's orbit and the apparent brightness of the stars. Using Newton's generalisation of Kepler's Third Law, which relates total mass, orbital period, and semi-major axis, together with the mass–luminosity relation, the distance can be determined. The masses of the two stars are initially estimated, typically as the mass of the Sun. Then, using Kepler's laws, the physical separation between the stars is calculated.
From this separation and the observed angular size, a preliminary distance from Earth is found. With that distance and the apparent magnitudes, the luminosities are computed, and the mass–luminosity relation yields revised masses. These new masses are used to recalculate the separation, and the process is iterated many times until convergence, achieving accuracies within 5%.
More in Binary and Multiple Stars
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Dynamical parallax (CC BY-SA 4.0).
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