spectroscopic binary

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Related to spectroscopic binary: eclipsing binary

spectroscopic binary:

see binary starbinary star
or binary system,
pair of stars that are held together by their mutual gravitational attraction and revolve about their common center of mass. In 1650 Riccioli made the first binary system discovery, that of the middle star in the Big Dipper's handle, Zeta
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Doppler shifts of spectral lines at various orbital positions of spectroscopic binaryclick for a larger image
Doppler shifts of spectral lines at various orbital positions of spectroscopic binary

spectroscopic binary

(spek-trŏ-skop -ik) A binary star in which the orbital motions of the components give rise to detectable variations in radial velocity, revealed by changes in Doppler shift in their spectral lines (see illustration). Because a binary star is more likely to be detected spectroscopically if its orbital period is relatively short and the orbital velocities are relatively high, most spectroscopic binaries are close binaries (see binary star). Spectroscopic detection is not possible if the orbital plane lies at right angles to the line of sight.

When the components are nearly equal in brightness both spectra are visible and the spectral lines appear double for most of each orbital period, coinciding only when the stars are moving at right angles to the line of sight. Such a system is called a double-lined spectroscopic binary. Comparison of the Doppler shifts in the component spectra gives the relative velocities and hence the relative masses of the two stars:

v 1 /v 2 = M 2 /M 1

The individual masses cannot be determined unless the inclination of the orbital plane to the line of sight is known (see eclipsing binary).

The presence of a comparatively faint component is revealed only by its gravitational effect on the motion of the brighter star. Invisible components of low mass are rarely detected because doppler shifts corresponding to orbital speeds of less than about 2 km s–1 are obscured by observational errors. See also mass function.

Spectroscopic Binary


a binary star whose component stars are so close together that they cannot be seen separately with even the most powerful telescopes. A spectroscopic binary can be distinguished from a single star only by observing periodic shifts or doubling of the binary’s spectral lines. This shift or doubling is caused by the Doppler effect, which results from the orbital motion of the component stars.

References in periodicals archive ?
Later, the fainter member of the Mizar double was also found to be a spectroscopic binary, as were well-known stars like Polaris, Spica, Capella, and Algol.
In fact Mizar's brighter component was the first spectroscopic binary discovered (in 1889, at Harvard College Observatory).
A popular misconception, repeated even in the Hipparcos catalog, is that Alcor is a spectroscopic binary, like each of the components of Mizar.
The components of this bright pair are individually magnitude 4.7 and 4.8, but it turns out that each is itself a spectroscopic binary. So when we gaze tonight at 3.9-magnitude Pi Lupi, some 500 light-years distant, we are looking at the combined light of a quadruple system.
On the other hand, as Massey and his colleagues note in the February 1st Astrophysical Journal, the 6.4-magnitude spectroscopic binary HD 92740 in Carina remains a strong contender, as it contains a Wolf-Rayet star with 55 [+ or -] 7 solar masses --a number that has enough wiggle room to perhaps set a record of its own one day.
[Alpha.sup.1] itself turns out to be a spectroscopic binary.
The Hyades star occulted by Nephele is a spectroscopic binary, so the disappearance and reappearance will likely occur in steps.

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