Electra (star)

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Electra
M45map.jpg
Electra's location (right center) in the Pleiades.
Observation data
Epoch J2000      Equinox J2000
Constellation Taurus
Right ascension 03h 44m 52.5373s[1]
Declination +24° 06′ 48.021″[1]
Apparent magnitude (V) 3.705[2]
Characteristics
Spectral type B6 IIIe[3]
U−B color index -0.40[4]
B−V color index -0.12[4]
Astrometry
Radial velocity (Rv) +10.9[5] km/s
Proper motion (μ) RA: 21.55[1] mas/yr
Dec.: -44.92[1] mas/yr
Parallax (π) 5.72 ± 1.05[6] mas
Distance approx. 600 ly
(approx. 170 pc)
Details
Surface gravity (log g) 3.412 ± 0.047[7] cgs
Temperature 13,484 ± 293[7] K
Rotation v sin i = 181 km/s[7]
Age 1.15 × 108[8] years
Other designations
17 Tauri, BD+23 507, FK5 136, GC 4477, HD 23302, HIP 17499, HR 1142, SAO 76131.
Database references
SIMBAD data

Electra, also designated 17 Tauri, is a blue-white giant star in the constellation of Taurus. The star is one of the nine brightest stars in the Pleiades open star cluster (M45). The most visible stars in this group are named for the Seven Sisters of Greek mythology.

Properties[edit]

The star has an apparent brightness of 3.72, the third-brightest of the stars in the group. Electra belongs to the spectral class B6 IIIe and is approximately 370 light-years from the Sun.[6] Electra is one of the four Pleiades stars that is classed as a giant; one that is starting to expand as the internal hydrogen fuel in the core is exhausted.

The projected rotational velocity of this star is 181 km/s, making it a fast rotator. This is the velocity component of the star's equatorial rotation along the line of sight to the Earth. The estimated inclination of the star's pole is 46.8° ± 1.6, giving it a true equatorial rotational velocity of 320 ± 18 km/s. The rapid rotation rate of this star flattens the poles and stretch the equator. This makes the surface gravity of the star non-uniform and causes temperature variation. This effect is known as gravity darkening, because it results in a variation of radiation by latitude. The rapid rotation extends the life span of the star by increasing the core density and reducing the radiation output.[7]

This is classified as a Be star, which is a B-type star with prominent emission lines of hydrogen in its spectrum.[3] The Be stars have a rotation rate that is 1.5–2 times the rotation of normal B-type stars. This high rate of rotation may allow mass loss during even minor prominences.[9] Changes in the radial velocity measurements indicate that this star may have a companion, which would make Electra a spectroscopic binary.[10][11]

Infrared observations of this star showed an excess level of radiation equal to about 0.5 magnitudes. This emission is probably from a gaseous disk created by radiation-driven mass loss and rapid rotation of the star. These disks are created by an ejection of material roughly every ten years, which then settles into the equatorial plane about the star. However, the bright nebulosity that surrounds this star makes the observation uncertain.[12]

Electra is periodically occulted by the Moon and occasionally by other planets in the Solar System. The last planetary occultation took place on May 9, 1841, when it was occulted by Venus.[citation needed]

Nomenclature[edit]

17 Tauri is the star's Flamsteed designation.

It bore the traditional name Electra.[13] Electra was one of the Pleiades sisters in Greek mythology. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars. The WGSN approved the name Electra for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[15]

Military namesakes[edit]

USS Electra (1843) and USS Electra (AK-21/AKA-4), both of United States Navy.

References[edit]

  1. ^ a b c d Perryman, M. A. C.; et al. (1997), "The Hipparcos Catalogue", Astronomy & Astrophysics, 323: L49–L52, Bibcode:1997A&A...323L..49P 
  2. ^ "NAME ELECTRA – Be Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2009-09-04. 
  3. ^ a b Grady, C. A.; Bjorkman, K. S.; Snow, T. P.; Sonneborn, George; Shore, Steven N.; Barker, Paul K. (April 1989). "Highly ionized stellar winds in Be stars. II - Winds in B6-B9.5e stars". Astrophysical Journal, Part 1. 339: 403–419. Bibcode:1989ApJ...339..403G. doi:10.1086/167306. 
  4. ^ a b Johnson, H. L.; Iriarte, B.; Mitchell, R. I.; Wisniewskj, W. Z. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99). Bibcode:1966CoLPL...4...99J. 
  5. ^ Pearce, J. A.; Hill, G. (1975). "A spectroscopic investigation of the Pleiades". Publications of the Dominion Astrophysical Observatory. 14 (14): 319–343. Bibcode:1975PDAO...14..319P. 
  6. ^ a b Makarov, Valeri V. (December 2002). "Computing the Parallax of the Pleiades from the Hipparcos Intermediate Astrometry Data: An Alternative Approach". The Astronomical Journal. 124 (6): 3299–3304. Bibcode:2002AJ....124.3299M. doi:10.1086/344683. 
  7. ^ a b c d Frémat, Y.; Zorec, J.; Hubert, A.-M.; Floquet, M. (September 2005). "Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars". Astronomy and Astrophysics. 440 (1): 305–320. arXiv:astro-ph/0503381Freely accessible. Bibcode:2005A&A...440..305F. doi:10.1051/0004-6361:20042229. 
  8. ^ Basri G.; Marcy G. W.; Graham J. R. (1996). "Lithium in Brown Dwarf Candidates: The Mass and Age of the Faintest Pleiades Stars". Astrophysical Journal. 458: 600–609. Bibcode:1996ApJ...458..600B. doi:10.1086/176842. 
  9. ^ Zorec, J.; Frémat, Y.; Cidale, L. (October 2005). "On the evolutionary status of Be stars. I. Field Be stars near the Sun". Astronomy and Astrophysics. 441 (1): 235–248. arXiv:astro-ph/0509119Freely accessible. Bibcode:2005A&A...441..235Z. doi:10.1051/0004-6361:20053051. 
  10. ^ Abt, Helmut A.; Barnes, Ronnie C.; Biggs, Eleanor S.; Osmer, Patrick S. (November 1965). "The Frequency of Spectroscopic Binaries in the Pleiades". Astrophysical Journal. 142: 1604–1615. Bibcode:1965ApJ...142.1604A. doi:10.1086/148440. 
  11. ^ Pearce, J. A.; Hill, Graham (1971). "Four Suspected Spectroscopic Binaries in the Pleiades". Publications of the Astronomical Society of the Pacific. 83 (494): 493–495. Bibcode:1971PASP...83..493P. doi:10.1086/129161. 
  12. ^ Gorlova, Nadya; Rieke, George H.; Muzerolle, James; Stauffer, John R.; Siegler, Nick; Young, Erick T.; Stansberry, John H. (October 2006). "Spitzer 24 μm Survey of Debris Disks in the Pleiades". The Astrophysical Journal. 649 (2): 1028–1042. arXiv:astro-ph/0606039Freely accessible. Bibcode:2006ApJ...649.1028G. doi:10.1086/506373. 
  13. ^ Allen, Richard Hinckley (1899). Star-names and their meanings. G. E. Stechert. p. 406. Retrieved 2009-10-10. 
  14. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  15. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016. 

External links[edit]