dynamical parallax

dynamical parallax

An iterative method used to determine the distance and the mass of a visual binary star, usually from measurements of the orbital period (P years) and apparent mean orbital size (l ″) and an estimate of the mass of the two stars (M ₁ + M ₂ solar masses). The approximate semimajor axis (a AU) of the orbit is calculated from Kepler's third law: (M ₁ + M ₂ )P ² = a ³

The ratio of a /l gives an estimate of the distance of the binary. If the apparent magnitude is known, the absolute magnitude can be deduced from the distance modulus and a more accurate value of total mass is hence obtained using the mass-luminosity relation. The process is repeated as necessary using the corrected mass estimates, an inaccurate estimate in mass leading to a much smaller error in distance.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

dynamical parallax

[dī¦nam·ə·kəl ′par·ə‚laks]

(astronomy)

A parallax of binary stars that is computed from the sum of the masses of the binary system.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.