Zeta Geminorum
 Location of ζ Geminoru (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Gemini |
| Right ascension | 07h 04m 06.53079s[1] |
| Declination | +20° 34′ 13.0739″[1] |
| Apparent magnitude (V) | 3.93 (3.68 to 4.16)[2] |
| Characteristics | |
| Spectral type | G0Ibv[3] (F7Ib to G3Ib)[4] |
| U−B color index | +0.55[5] |
| B−V color index | 0.88[5] |
| Variable type | Classical Cepheid |
| Astrometry | |
| Radial velocity (Rv) | +6.7[6] km/s |
| Proper motion (μ) | RA: –7.29[1] mas/yr Dec.: –0.41[1] mas/yr |
| Parallax (π) | 2.37 ± 0.30[1] mas |
| Distance | approx. 1400 ly (approx. 420 pc) |
| Details | |
| Radius | (65.24 ± 0.20) ± 4.17[7] R☉ |
| Surface gravity (log g) | 1.9[8] |
| Temperature | 5,260–5,780[4] K |
| Metallicity [Fe/H] | 0.16[8] dex |
| Rotational velocity (v sin i) | 19[9] km/s |
| Other designations | |
Zeta Geminorum (ζ Gem, ζ Geminorum) is a star in the zodiac constellation Gemini. It is located on the outstretched left 'leg' of the twin Pollux. This star has the traditional name Mekbuda, which comes from ancient Arabic where it and the star Mebsuta (Epsilon Geminorum) were the paws of a lion. Mekbuda comes from a phrase meaning the lion's folded paw.[10]
In Chinese, 井宿 (Jǐng Su), meaning Well (asterism), refers to an asterism consisting of ζ Geminorum, μ Geminorum, γ Geminorum, ν Geminorum, ξ Geminorum, ε Geminorum, 36 Geminorum and λ Geminorum.[11] Consequently, ζ Geminorum itself is known as 井宿七 (Jǐng Su qī, English: the Seventh Star of Well.)[12]
[edit] Observation history
In 1825, German astronomer Julius Schmidt discovered that this star varies in brightness with a period of about 10 days,[10] although it had been suspected of variability as early as 1790.[13] In 1899, American astronomer W. W. Campbell announced that Zeta Geminorum has a variable radial velocity.[14] (This variation was independently discovered by Russian astronomer Aristarkh Belopolsky, published in 1901.)[13] Based on his observations, Campbell later published orbital elements for the binary. However, he found that the curve departed from a keplerian orbit and even suggested that it was a triple star system in order to explain the irregularities.[15] The periodic variation in radial velocity was subsequently explained as the result of radial pulsations that occur in a class of variable stars known as Cepheid variables—named after Delta Cephei.[13]
The periodicity of the star is itself variable, a trend first noted by German astronomer Paul Guthnick in 1920, who suspected that the period change was the result of an orbiting companion. In 1930, Danish astronomer Axel Nielsen suggested that the change was instead the result in a steady decrease of about 3.6 seconds per year in the period.[16]
[edit] Properties
This star is a Classical Cepheid variable that undergoes regular, periodic variation in luminosity because of radial pulsations. In the V band, the apparent magnitude varies between a high of 3.68 and a low of 4.16 (with a mean of 3.93) over a period of 10.148 days.[2] This period of variation is decreasing at the rate of 3.1 seconds per year, or 0.085 seconds per cycle.[16] It has a nominal stellar classification of G0 Ibv,[3] with the luminosity class of Ib indicating that this is an intermediate luminous supergiant. The 'v' suffix means that it has variable spectral features, with the actual classification changing between F7Ib and G3Ib over the course of a pulsation cycle. Likewise the effective temperature of the outer envelope varies between 5,780 K and 5,260 K,[4] while the radius varies from 61 to 69 times the Sun's radius.[7]
There is no evidence of a stellar companion to Zeta Geminorum.[16] Based upon parallax measurements, this star is located at a distance of about 1,400 light-years (420 parsecs) from Earth.[1]
[edit] References
- ^ a b c d e f van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
- ^ a b Klagyivik, P.; Szabados, L. (September 2009), "Observational studies of Cepheid amplitudes. I. Period-amplitude relationships for Galactic Cepheids and interrelation of amplitudes", Astronomy and Astrophysics 504 (3): 959–972, Bibcode 2009A&A...504..959K, doi:10.1051/0004-6361/200811464
- ^ a b c "V* zet Gem -- Classical Cepheid (delta Cep type)", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Zeta+Geminorum, retrieved 2012-01-01
- ^ a b c Kervella, P. et al. (March 2001), The angular diameter and distance of the Cepheid ζ Geminorum, 367, pp. 876–883, Bibcode 2001A&A...367..876K
- ^ a b Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Observatory, Bibcode 1978ppch.book.....N
- ^ Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, Bibcode 1999VeARI..35....1W
- ^ a b Groenewegen, M. A. T. (November 2007), "The projection factor, period-radius relation, and surface-brightness colour relation in classical cepheids", Astronomy and Astrophysics 474 (3): 975–981, Bibcode 2007A&A...474..975G, doi:10.1051/0004-6361:20078225
- ^ a b Mallik, Sushma V. (October 1998), "Chromospheric activity in cool stars and the lithium abundance", Astronomy and Astrophysics 338: 623–636, Bibcode 1998A&A...338..623M
- ^ Uesugi, Akira; Fukuda, Ichiro (1970), "Catalogue of rotational velocities of the stars", Contributions from the Institute of Astrophysics and Kwasan Observatory (University of Kyoto), Bibcode 1970crvs.book.....U
- ^ a b Allen, Richard Hinckley (1899), [books.google.com/books?id=5xQuAAAAIAAJ&pg=PA235 Star-names and their meanings], G. E. Stechert, p. 235, books.google.com/books?id=5xQuAAAAIAAJ&pg=PA235
- ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ^ a b c Henroteau, F. (1925), "A study of zeta Geminorum, I.", Publications of the Dominion Observatory Ottawa 9: 105–116, Bibcode 1925PDO.....9..105H
- ^ Campbell, W. W. (February 1899), "The variable velocity of zeta Geminorum in the line of sight.", Astrophysical Journal 9: 86, Bibcode 1899ApJ.....9...86C, doi:10.1086/140556
- ^ Campbell, W. W. (January 1901), "The motion of zeta Geminorum in the line of sight", Astrophysical Journal 13: 90–97, Bibcode 1901ApJ....13...90C, doi:10.1086/140792
- ^ a b c Abt, Helmut A.; Levy, Saul G. (March 1974), "Period Variation of the Cepheid Zeta Geminorum", Astrophysical Journal 188: L75, Bibcode 1974ApJ...188L..75A, doi:10.1086/181436
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