Thursday, November 19, 2015

Lyra - Aladfar η Lyrae Blue subgiant

Alcyone, Pleiades, is a typical blue giant
NASA, ESA, AURA/Caltech, Palomar Observatoryderivative work:
Roberto Segnali all'Indiano - Pleiades_large.jpg. Licensed under Public Domain via Commons

Eta Lyrae is a blue subgiant with nearly similar metal abundance to Sun. The star belongs to spectral class B2.5IV and has apparent magnitude of +4.40.  It is approximately 1390 light years from Earth.

The originally Arabic name Aladfar الأظفر al-’uz̧fur means "the talons (of the swooping eagle)" with Arab astronomers association of Lyra with an eagle.

Blue giants
Blue giant Bellatrix compared to Algol B, the Sun, a red dwarf, and some planets
Image by User:84user, User:Paul Stansifer and others
Licensed under GPLv2 via Commons
Blue giant is a hot star with a luminosity class of III (giant) or II (bright giant). In the standard Hertzsprung–Russell diagram, these stars lie above and to the right of the main sequence.

The name is applied to a wide variety of different types of stars with a moderate increase in size and luminosity compared to main-sequence stars of the same mass or temperature, and are hot enough to be called blue, meaning spectral class O, B, and sometimes early A.

Stars found in the blue giant region of the HR diagram can be in very different stages of their lives, but all are evolved stars that have largely exhausted their core hydrogen supplies.

Blue giants have temperatures from around 10,000 K upwards, ZAMS masses greater than about twice the Sun (M☉), and absolute magnitudes around 0 or brighter. These stars are only 5–10 times the radius of the Sun (R☉), compared to red giants which are up to 100 R☉.

Blue giants are much rarer than red giants, because they only develop from more massive and less common stars, and because they have short lives in the blue giant stage.

Hertzsprung–Russell diagram
by User:Rursus. Licensed under CC BY-SA 3.0 via Commons

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