[edit]The Pleiades Cluster in infrared with Electra at the very top of the frame
Electra has an apparent brightness of 3.72, the third-brightest of the stars in the group. It belongs to the spectral class B6 IIIe and is approximately 400 light-years from the Sun.[1] The Pleiades cluster is thought to be 444 light-years away. A number of papers have reported Electra to be a multiple star, but these have been contradictory and never confirmed.[13]
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.[10]
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.[8] Changes in the radial velocity measurements indicate that this star may have a companion, which would make Electra a spectroscopic binary.[14][15] However, follow-up studies including interferometry have failed to confirm any companion star(s), so it is likely a single star.[16]
Alight curve for Electra, adapted from White et al. (2017)[17]
Electra may be a variable star, and it appears in the New Catalogue of Suspected Variable Stars as NSV 15755.
Low amplitude variability of the brightness of Electra was detected by Kepler/K2, and Fourier analysis of the star's light curve shows several periods of oscillation, the strongest being 1.107 and 1.165 days.[17] The International Variable Star Index classifies it as a slowly pulsating B star.[18]
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.[19]
^Ducati, J. R (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
^ abGrady, 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.
^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: 99–110. Bibcode:1966CoLPL...4...99J.
^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.
^Harmanec, P (2000). "Physical Properties and Evolutionary Stage of Be Stars". The be Phenomenon in Early-Type Stars. 214: 13. Bibcode:2000ASPC..214...13H.
^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. S2CID121363965.
^"NSV 15755". The International Variable Star Index. AAVSO. Retrieved 8 October 2022.
^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. S2CID17227369.
