Maia (star)

Maia, designated 20 Tauri (abbreviated 20 Tau), is a star in the constellation of Taurus. It is a blue giant of spectral type B8 III, a chemically peculiar star, and the prototype of the Maia variable class of variable star.

Maia is the fourth-brightest star in the Pleiades open star cluster (Messier 45), after Alcyone, Atlas and Electra. It is surrounded by one of the brighter reflection nebulae within the Pleiades, designated NGC 1432 and sometimes called the Maia Nebula.

Nomenclature
The name Maia originates with the Μαῖα and Maia. Maia is one of the seven daughters of Atlas and Pleione in Greek mythology&mdash;stars which are also included in the Pleiades star cluster. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Maia for this star. It is now so entered in the IAU Catalog of Star Names.

20 Tauri is the star's Flamsteed designation. Although it is about the 15th brightest star in Taurus, Maia does not have a Bayer designation, but does have the Bright Star Catalogue designation HR 1149 and the Henry Draper Catalogue designation HD 23408. It has been listed as double star WDS J03458+2422; one companion is a 14th magnitude star nearly $2 '$ away that is probably an unrelated background object. The primary is listed as being double following observations of a lunar occultation, but later observations have failed to find any evidence of it being double.

Description
The distance to Maia has been measured by the Gaia spacecraft using the annual parallax method. In Gaia Data Release 2, the parallax is given as $9.479 mas$, corresponding to a distance of $106 pc$. The 2007 new Hipparcos reduction gives a statistically more accurate parallax of $8.51 mas$, indicating a distance of $118 pc$. Analysis of Gaia parallaxes for the whole Pleiades cluster give an average distance of $136.2 pc$, while VLBI measurements of multiple members give a distance of $136.2 pc$.

Maia's visual magnitude is 3.87, requiring darker skies to be seen. Its bolometric luminosity is 501 times solar, mostly in the ultraviolet, thus suggesting a radius that is 3.6 times that of the Sun and a mass that is 3.8 times solar. Interferometric measurements give an angular diameter of $0.436 mas$, suggesting a radius of assuming a distance of $113.5 pc$. These measurements also allow the effective temperature to be estimated at $14,700 K$.

Maia is a chemically peculiar star, meaning it has an unusual surface abundance of some elements as shown by its spectral lines. It is classified as a helium-weak star, but it also shows an excess of some elements including manganese.

Maia was thought to be a variable star by astronomer Otto Struve. He proposed a class of stars known as Maia variables, which included Gamma Ursae Minoris. Examination of the Hipparcos data for Maia and some others in the class found no evidence of variability. On the other hand, White et al. found low amplitude, but unambiguous, variability in Maia's brightness as seen by Kepler/K2, with a period of 10.3 days, which they attribute to the rotation of a starspot. Intense study of large numbers of stars suggest that 6.7% of stars with temperatures between $10,000 K$ and $18,000 K$ show rapid small-amplitude pulsations but are not members of other variable star classes. These are potentially Maia variables. Ironically, if the White et al. results are correct, Maia is a variable star, but not a Maia variable star.

Maia is surrounded by the Maia Nebula (also known as NGC 1432), a reflection nebula that is one of the brightest patches of nebulosity within the Pleiades star cluster. It is the only member of the New General Catalogue discovered photographically.

Mythology
Maia was the oldest of seven beautiful sisters known as the Pleiades. She was impregnated by Zeus, thereby conceiving Hermes, the messenger god. As Maia and the Pleiades are visible in the winter night sky along with the constellation Orion, the Greek myths tell of Maia and her sisters being pursued by the giant huntsman and turned into doves to preserve their safety.