Double star
In
This occurs because the pair either forms a
Since the beginning of the 1780s, both professional and amateur double star observers have telescopically measured the distances and angles between double stars to determine the relative motions of the pairs.
The following are three types of paired stars:
- Optical doubles are unrelated stars that appear close together through chance alignment with Earth.
- Visual binaries are gravitationally bound stars that are separately visible with a telescope.
- Non-visual binaries are stars whose binary status was deduced through more esoteric means, such as occultation (eclipsing binaries), spectroscopy (spectroscopic binaries), or anomalies in proper motion (astrometric binaries).
Improvements in telescopes can shift previously non-visual binaries into visual binaries, as happened with Polaris A in 2006.[5] It is only the inability to telescopically observe two separate stars that distinguishes non-visual and visual binaries.
History
The unrelated categories of optical doubles and true binaries are lumped together for historical and practical reasons. When Mizar was found to be a binary, it was quite difficult to determine whether a double star was a binary system or only an optical double. Improved telescopes, spectroscopy,[10] and photography are the basic tools used to make the distinction. After it was determined to be a visual binary, Mizar's components were found to be spectroscopic binaries themselves.[11]
Observation of double stars
Observation of visual double stars by visual measurement will yield the separation, or angular distance, between the two component stars in the sky and the position angle. The position angle specifies the direction in which the stars are separated and is defined as the bearing from the brighter component to the fainter, where north is 0°.[13] These measurements are called measures. In the measures of a visual binary, the position angle will change progressively and the separation between the two stars will oscillate between maximum and minimum values. Plotting the measures in the plane will produce an ellipse. This is the apparent orbit, the projection of the orbit of the two stars onto the celestial sphere; the true orbit can be computed from it.[14] Although it is expected that the majority of catalogued visual doubles are visual binaries,[15] orbits have been computed for only a few thousand of the over 100,000 known visual double stars.[16][17]
Distinction between binary stars and other double stars
Confirmation of a visual double star as a binary star can be achieved by observing the relative motion of the components. If the motion is part of an
Designations
Some bright visual double stars have a
Apart from these pairs, the components of a double star are generally denoted by the letters A (for the brighter, primary, star) and B (for the fainter, secondary, star) appended to the designation, of whatever sort, of the double star. For example, the components of
Discoverer | Traditional code | WDS code |
---|---|---|
Brisbane Observatory
|
Brs0 | BSO |
S. W. Burnham
|
β | BU |
James Dunlop | Δ | DUN |
William Herschel | H I, II, etc. | H 1, 2, etc. |
N. Lacaille
|
Lac | LCL |
F. G. W. Struve
|
Σ | STF |
Struve Appendix Catalogue I | Σ I | STFA |
Struve Appendix Catalogue II | Σ II | STFB |
Otto Struve | OΣ | STT |
Pulkova Appendix Catalogue | OΣΣ | STTA |
Visual doubles are also designated by an abbreviation for the name of their discoverer followed by a catalogue number unique to that observer. For example, the pair α Centauri AB was discovered by Father Richaud in 1689, and so is designated RHD 1.
The Washington Double Star Catalog, a large database of double and multiple stars, contains over 100,000 entries,[16] each of which gives measures for the separation of two components. Each double star forms one entry in the catalog; multiple stars with n components will be represented by entries in the catalog for n−1 pairs, each giving the separation of one component of the multiple star from another. Codes such as AC are used to denote which components are being measured—in this case, component C relative to component A. This may be altered to a form such as AB-D to indicate the separation of a component from a close pair of components (in this case, component D relative to the pair AB.) Codes such as Aa may also be used to denote a component which is being measured relative to another component, A in this case.[22] Discoverer designations are also listed; however, traditional discoverer abbreviations such as Δ and Σ have been encoded into a string of uppercase Roman letters, so that, for example, Δ65 has become DUN 65 and Σ2451 has become STF 2451. Further examples of this are shown in the adjacent table.[20][23]
Examples
Visual binaries
- Acrux
- Capella
- p Eridani
- Polaris
- Procyon
- Sirius
- Alpha Centauri system (AB) and Proxima Centauri (thus α Cen C): Actually a three-star system
Optical doubles
- Alpha1 and Alpha2 Capricorni
- Theta Muscae and Theta Muscae B
- Eta1 and Eta2 Coronae Australis
- Kappa1 and Kappa2 Coronae Australis
- Winnecke 4 (Messier 40)
- Polaris and Gamma Cephei, twin polar stars; Precession predicts Gamma Cephei should return to prominence by the year 3000.[25]
Uncertain
- Castor system (Aa/Ab/Ba/Bb) and YY Geminorum (thus Castor Ca/Cb) is generally considered a physical system
- Mizarsystem (Aa/Ab/Ba/Bb) and Alcor (itself a binary, thus Mizar Ca/Cb, though generally not considered physical until 2009)
References
- ^ a b c Aitken, R. G. (1964). The Binary Stars. New York: Dover. p. 1.
- ^ ISBN 90-277-0885-1.
- S2CID 6052794.
- ISBN 90-277-0885-1.
- ^ "Artist's Concept of Polaris System - Annotated". HubbleSite. Space Telescope Science Institute.
- ^ A New View of Mizar Archived 2008-03-07 at the Wayback Machine, Leos Ondra, accessed on line May 26, 2007.
- ^ Aitken, Robert G. (1935). The Binary Stars. New York: McGraw-Hill. p. 1.
- Bibcode:1954AJ.....59...61S.
- ^ The Binary Stars, Robert Grant Aitken, New York: Dover, 1964, p. 260.
- ^ Fraunhofer, 1814
- ^ Pickering, 1889
- ^ "Masquerading as a double star". ESA/Hubble Picture of the Week. Retrieved 25 March 2013.
- ISBN 1-85233-558-0.
- ISBN 1-85233-558-0.
- ISBN 90-277-0885-1.
- ^ a b "Introduction and Growth of the WDS", The Washington Double Star Catalog Archived 2008-09-17 at the Wayback Machine, Brian D. Mason, Gary L. Wycoff, and William I. Hartkopf, Astrometry Department, United States Naval Observatory, accessed on line August 20, 2008.
- ^ Sixth Catalog of Orbits of Visual Binary Stars Archived 2009-04-12 at the Wayback Machine, William I. Hartkopf and Brian D. Mason, United States Naval Observatory, accessed on line August 20, 2008.
- ISBN 90-277-0885-1.
- ISBN 90-277-0885-1.
- ^ ISBN 1-85233-558-0.
- ^ Entry 14396-6050, discoverer code RHD 1AB,The Washington Double Star Catalog Archived 2012-07-08 at archive.today, United States Naval Observatory. Accessed on line August 20, 2008.
- ^ Format of the current WDS Archived April 12, 2008, at the Wayback Machine, Washington Double Star Catalog, United States Naval Observatory. Accessed on line August 26, 2008.
- ^ References and discoverer codes, The Washington Double Star Catalog Archived 2008-04-13 at the Wayback Machine, United States Naval Observatory. Accessed on line August 20, 2008.
- ^ "ALMA Finds Double Star with Weird and Wild Planet-forming Discs". ESO Press Release. Retrieved 1 August 2014.
- ISBN 978-0-399-57953-0, First edition.