Friday, November 20, 2015

Lyra - Alathfar and spectral class A

Fomalhaut,(Alpha Piscis Austrini) is an A3 main-sequence star
"Heic0821f" by Davide De Martin
Licensed under Public Domain via Commons

Mu Lyrae (μ Lyr, μ Lyrae) is main-sequence dwarf star with apparent magnitude 5.12. It belongs to the spectral class A0IV.  Located around 439 light-years distant, it shines with a luminosity approximately 125 times that of the Sun and has a surface temperature of 8190 K.

The star has the traditional name Alathfar, from the Arabic الأظفر al-’uz̧fur "the talons (of the swooping eagle)", a name it shares with Eta Lyrae (usually spelled with d instead of th: Aladfar).

Let me repeat: luminosity of 125 times that of the Sun.

A-type stars 
These are among the more common naked eye stars and are white or bluish-white.

They have strong hydrogen lines, at a maximum by A0, and also lines of ionized metals (Fe II, Mg II, Si II) at a maximum at A5. The presence of Ca II lines is notably strengthening by this point.

About 1 in 160 (0.625%) of the main-sequence stars in the solar neighborhood are A-type stars.

Spectral standards:
  • A0Van: Gamma Ursae Majoris
  • A0Va: Vega
  • A0Ib: Eta Leonis
  • A0Ia: HD 21389
  • A2Ia: Deneb
  • A3Va: Fomalhaut

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