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Unformatted text preview: 67 Laboratory 10 Measuring the Properties of Binary Stars Materials Used: Spectral data from the eclipsing binary star system JR-M 60; an Excel spreadsheet with system parameters, a light curve, velocity curves and spectral data; a Hertzsprung-Russell diagram. Objectives: To study methods for determining the various properties of stars in binary systems. Discussion: Measuring the physical properties of stars is an area of great interest in astronomy. Stars are the most numerous and important large objects in the Universe. Because of the great distances from us to all stars (except our own) it is only possible for us to observe and measure their properties from afar by indirect methods. Binary systems systems containing two stars that orbit around the same center of mass - are of considerable importance in the realm of stellar measurements. Because binary stars orbit each other their combined masses may be easily determined. All that is necessary to determine the mass of a binary system is to measure the period and semimajor axis of the system. If the orbital velocities of the individual stars are determined from spectral data (or some other means) the individual masses of the stars may then be computed with relative ease. The sizes, surface temperatures and luminosities of the individual stars and the distance of the system from us follow. Binary stars are quite common and their abundance allows astronomers to classify a wide variety of stars based on the study of binary systems. A fundamental precept of astronomy is that what seems easy to accomplish in theory is almost invariably more difficult in practice and stellar measurements are no exception to this rule. Even the properties of stars in binary systems are not determined without fairly sophisticated methods. In this procedure we will concentrate on a particularly useful type of binary system known as an eclipsing binary . Eclipsing binaries are relatively rare (only a few thousand are known) but lend themselves to analysis due to their simple geometry and alignment with respect to our viewing angle. Eclipsing binaries consist of two stars that are relatively close to each other so much so that they often appear as a single point of light to observers on Earth. An eclipsing binary may, in fact, first appear to be a single variable star. Exceptionally large changes in apparent magnitude and cyclic Doppler shift data are indicative of a pair of closely spaced stars. Eclipsing binaries orbit in a plane nearly parallel to our line of sight and the brightness of the system changes periodically as the stars pass in front of each other. This variation in the brightness may be used to plot a light curve a graph of brightness vs. orbital position for the system....
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This note was uploaded on 01/16/2012 for the course PHYS 153 taught by Professor Hackwrth,m during the Spring '08 term at Idaho State University.
- Spring '08