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.

Electra, also cataloged as 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 cluster. The most visible stars in this group are named for the Seven Sisters of Greek mythology.

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 our solar system. The last planetary occultation took place on May 9, 1841, when it was occulted by Venus.[citation needed]

Electra in Military[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/0503381. 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/0509119. 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/0606039. Bibcode:2006ApJ...649.1028G. doi:10.1086/506373. 

External links[edit]