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Electra (star)
Encyclopedia
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. 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 , giving it a true equatorial rotational velocity of . 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.
This is classified as a Be star
, which is a B-type star with prominent emission lines of hydrogen
in its spectrum. 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. Changes in the radial velocity
measurements indicate that this star may have a companion, which would make Electra a spectroscopic binary.
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.
Electra is periodically occulted
by the Moon
and occasionally by other planet
s in our solar system. The last planetary occultation took place on May 9, 1841, when it was occulted by Venus.
, both of United States
Navy
.
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Taurus
Taurus (constellation)
Taurus is one of the constellations of the zodiac. Its name is a Latin word meaning 'bull', and its astrological symbol is a stylized bull's head:...
. The star is one of the nine brightest stars in the Pleiades
Pleiades (star cluster)
In astronomy, the Pleiades, or Seven Sisters , is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky...
open cluster
Open cluster
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...
. The most visible stars in this group are named for the Seven Sisters
Pleiades (Greek mythology)
The Pleiades , companions of Artemis, were the seven daughters of the titan Atlas and the sea-nymph Pleione born on Mount Cyllene. They are the sisters of Calypso, Hyas, the Hyades, and the Hesperides...
of Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
.
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. 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
Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface....
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 , giving it a true equatorial rotational velocity of . 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
Gravity darkening
Gravity darkening, also referred to as Gravity Brightening, is an astronomical phenomenon where a star rotates so rapidly that it has a detectably oblate spheroid shape, such as in Regulus in the Leo constellation....
, 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.
This is classified as a Be star
Be star
A Be star is a B-type star with prominent emission lines of hydrogen in its spectrum. The designation is combined by the spectral class, B, and the lowercase e denoting emission in the spectral classification system. Line emission from other atomic ions might be present as well, but is typically...
, which is a B-type star with prominent emission lines of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
in its spectrum. 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. Changes in the radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
measurements indicate that this star may have a companion, which would make Electra a spectroscopic binary.
Infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
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.
Electra is periodically occulted
Occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...
by the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
and occasionally by other planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s in our solar system. The last planetary occultation took place on May 9, 1841, when it was occulted by Venus.
Electra in Military
USS Electra (1843) and USS Electra (AK-21/AKA-4)USS Electra (AKA-4)
USS Electra was an Arcturus-class attack cargo ship named after Electra, a star in the Pleiades star cluster in the constellation Taurus. She served as a commissioned ship for seven years....
, both of United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
.