Pleione Facts

Pleione is the seventh-brightest star in the Pleiades star cluster. It is located at around 392 light-years away from the Sun. Keep reading for comprehensive facts and information.

Pleione, designated as 28 Tauri, is a binary star located in the zodiacal constellation of Taurus, the celestial bull. Pleione is also among the nine brightest Pleiades stars.

Key Facts & Summary

  • Pleione is the seventh-brightest star in the Pleiades star cluster. It is located at around 392 light-years away from the Sun.
  • Pleione is a binary star, composed out of the primary star, Pleione, a bluish-white main-sequence star of spectral type B8IVpe, and a companion whose properties are uncertain.
  • The apparent magnitude of this star is 5.048 however, it is a Gamma Cassiopeiae variable star, exhibiting variations from magnitude 4.8 to 5.5.
  • These periodic changes are caused by two circumstellar disks that are positioned at different angles.
  • Pleione is classified as a Be star due to these traits, it is also a very fast-spinning star, having a rotational velocity of around 329 kilometers / 204.4 miles per second.
  • This speed is very close to the star’s breaking point.
  • Pleione is bigger than our Sun, having an estimated 3.4 solar masses, and 3.2 solar radii.
  • This star is approximately 190 times brighter than our Sun.
  • The radial velocity of Pleione has been estimated to be at 4.4 km / 2.7 mi per second.
  • Surface average temperatures on Pleione are around 12,000 K, much hotter than on our Sun.
  • The zodiacal constellation of Taurus, and the Pleiades open cluster, were known to the ancients.
  • The Pleiades cluster is very bright, though, it cannot be seen during May and June since the Sun blocks our view of the cluster in that period.
  • Though Pleione is a fifth magnitude star, it is difficult to observe it with the naked eye since the star is positioned in the sky very near to the brighter star, Atlas, making it almost indistinguishable.

The star, Pleione, is named after a character from Greek mythology, namely, the wife of the Titan Atlas. Pleione was an Oceanic nymph, one of the three thousand daughters of the Titans Oceanus and Tethys.

Pleione’s husband, the Titan Atlas, was later condemned to carry the heavens on his shoulders after he was defeated by the gods, his wife, Pleione, would later give birth to the Hyades, the archer Hyas, and the Pleiades.

Both the names Pleione and Pleiade derive from Greek and roughly translate to “to sail”, hence the reason why Pleione is sometimes referred to as the “sailing queen”, and the Pleiades as the “sailing ones”.

Another variant for the name origin for Pleione might also translate to “plenty” or “many”, while the Pleiades may come from a different Greek word that would translate to “doves”.

The reference to doves might suit well the myth since Zeus, the supreme Greek god, transformed the sisters into doves to protect them from Orion.

Formation

Pleione, along with its neighboring stars in the Pleiades cluster, formed between 75 and 150 million years ago. This open cluster is among the closest star clusters to Earth.

All the stars in the Pleiades cluster have a common origin, they formed through a gigantic molecular cloud of dust and gas. Gravity pulled the swirling gas and dust together and formed the Pleiades cluster.

The Pleiades cluster is overall dominated by very hot blue and luminous stars.

Distance, Size, and Mass

Pleione is located at around 392 light-years / 120 parsecs away from Earth. It is the smallest of the Pleiades stars, but still bigger than our Sun.

Pleione has 3.2 solar radii, or 320% of the Sun’s radius, and 3.4 solar masses, or 340% of our Sun’s mass. Based upon its radius, Pleione is around six times bigger than our Sun.

Other Characteristics

Pleione is a bluish-white main-sequence star of spectral type B0IVpe (indicating a subgiant), or a B8Vne (indicating a hydrogen fusing dwarf), depending upon the source.

The suffix “pe” is an indicator of a peculiarity in emission lines, referring to emissions that come from the circumstellar disks of material expelled by the star.

The “ne” indicates a fast-spinning star classified as a Be star, that displays emission lines in its spectrum, suggesting the presence of an equatorial disk of gas.

Pleione is classified as a Be star and a Gamma Cassiopeiae variable, and it has the variable star designation BU Tauri along with the Flamsteed designation 28 Tauri.

Gamma Cassiopeiae variables are stars that exhibit brightness variations by about a magnitude over several decades. The variations are caused by shell features that appear in their spectra.

In the case of Pleione, it exhibits periodic changes due to two circumstellar disks positioned at different angles, and thus its brightness varies from magnitude 4.8 to 5.5.

Pleione also has a fast rotation speed, around 329 kilometers / 204.4 miles per second. This is quite close to its breakup velocity ( at 390 km).

Pleione is spinning faster even than Regulus ( 318 km ), and Achernar (250 km). Because of this high-speed rotation, Pleione has strong stellar winds, and it is losing mass at a high rate. Pleione turns on its axis once every 11.8 hours, while our Sun at 25.3 days, for comparison.

Pleione is approximately 190 times brighter than our Sun, while its surface average temperatures were recorded at around 12,000 K, twice the temperatures of our Sun.

Stellar System

Pleione is a single-lined spectroscopic binary star. This was discovered in 1996. The angular diameter between the two stars is 0.2 arcseconds – 24 AU.

The stars have an orbital period of 218 days. Though much is known about the primary star, Pleione, its companion remains a mystery. However, Pleione is a special star nonetheless.

This is because of the presence of a double-disk structure with disks positioned at different angles, surrounding Pleione, a unique feature among known stars.

Location

Pleione is located in the zodiacal constellation of Taurus, the celestial bull. It is the seventh-brightest star of the famous Pleiades open cluster. The Constellation of Taurus is also home to another great open cluster named Hyades.

This constellation is among the largest in the night sky, and also one of the most prominent of the northern constellations occupying an area of 797 square degrees.

The constellation of Taurus, apart from the two mentioned clusters, also has many interesting stars such as Aldebaran, Elnath, and also other fascinating deep-sky objects such as the Crab Nebula, Crystal Ball  Nebula, merging galaxies and many more open clusters.

These celestial objects are best observed and studied during January.

Pleiades Member

Pleione is the seventh-brightest star of the Pleiades open cluster. From October to April, these stars can be observed and studied, however, May and June are not suitable for observation since the cluster is too close to the Sun.

The Pleiades open cluster is among the closest star clusters to Earth, and one of the brightest in our vicinity. Though the cluster is very bright and easy to find, you may also draw an imaginary line from the stars of Orion’s Belt – AlnitakAlnilam, and Mintaka  – past Aldebaran – and find the cluster.

The Pleiades cluster is also known as Messier 45. The majority of the brightest and hottest stars here are of spectral class B, and they formed between 75 and 150 million years ago.

Most of them are far apart from each other, and at around 444 light-years away from us. The most documented and famous stars are all named after the mythological Seven Sisters and their parents from Greek mythology.

The nine stars are Alcyone, Asterope, Atlas, Electra, Celaeno, Maia, Merope, Taygeta, and Pleione. The mythological story depicts the sisters as they caught the eye of Orion, a giant huntsman. Atlas, being condemned for his battles against the gods, was condemned to carry the heavens on his shoulders while Orion, the giant, pursued his daughters. 

However, the Greek god Zeus stepped in and transformed the sisters into doves, and then into stars to console their father. Even so, Orion, the giant, is still pursuing the Pleiades sisters across the sky, represented by the Orion constellation.

The Future

Alcyone will continue to exist for many millions of years however, the Pleides star cluster has been studied closely and many computer simulations predict a grim future. 

Most simulations suggest that the cluster will continue to survive for 250 million years before it will start to disperse due to gravitational interactions with its galactic neighborhood.

Did you know?

  • Among the nine brightest stars in the Pleiades cluster, Pleione, among with Asterope, are the only ones still on the main-sequence, fusing hydrogen in their cores.
  • Atlas and Pleione are less than 5 arcminutes apart, however, Pleione is more difficult to oberve with the naked eye since it is fainter.
  • The Pleiades star cluster is believed to have been formed from a compact configuration that resembled the Orion Nebula.
  • Many cultures throughout the world knew of the Pleiades cluster since ancient times. One of the earliest depictions of the Pleiades cluster and its stars resides in the Nebra sky disk – a Bronze Age artifact dating to 1.6000 BCE, uncovered in Germany.
  • Many famous and ancient texts mention the cluster, such as Homer’s Illiad and Odyssey, Hesiod’s Works and Days, the Bible, the ancient Egyptian Calendar of Lucky and Unlucky Days, and the Japanese Kojiki – An Account of Ancient Matters – the 8th-century chronicle of myths, oral traditions, and legends.
  • The Pleiades are mentioned in the Kojiki as the Mutsuraboshi – translating to “six stars.” In modern Japan, the cluster is now known as Subaru – the same name used by the famous automobile company that depicts the six brightest stars in their logo.
  • One of the first telescopic observations conducted on the Pleiades was during the 1610s. Galileo Galilei observed the bright stars and the cluster and it is noted that he may well be the first to have done so.

Sources:

  1. Wikipedia
  2. Star-facts
  3. Britannica 

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