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Type of Tau Ceti and Toliman



 
 
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  #1  
Old February 20th 21, 10:20 PM posted to sci.astro.research
Jos Bergervoet
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Posts: 126
Default Type of Tau Ceti and Toliman

Why is Tau Ceti a G-type star and Toliman (Alpha Cen B) a K-type?

In terms of mass, Tau Ceti is actually the lighter one (78% of the
Sun's mass vs. 90% for Toliman.) So you'd expect the opposite..

https://en.wikipedia.org/wiki/Tau_Ceti
https://en.wikipedia.org/wiki/Alpha_...pha_Centauri_B

--
Jos

[[Mod. note -- One plausible reason is that stars change in spectral
type as they age. Wikipedia gives Tau Ceti's age as 5.8 Gyr, Alpha Cen B
as 5.3 Gyr. The two stars also have somewhat different metallicities
(which affect spectral types).
-- jt]]
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  #2  
Old February 21st 21, 12:45 AM posted to sci.astro.research
Phillip Helbig
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Posts: 38
Default Type of Tau Ceti and Toliman

In article , Jos Bergervoet
writes:

Why is Tau Ceti a G-type star and Toliman (Alpha Cen B) a K-type?

In terms of mass, Tau Ceti is actually the lighter one (78% of the
Sun's mass vs. 90% for Toliman.) So you'd expect the opposite..

https://en.wikipedia.org/wiki/Tau_Ceti
https://en.wikipedia.org/wiki/Alpha_...pha_Centauri_B


Note that Tau Ceti is G8, while the Sun is G2. After G comes K, so the
difference between G8 and K isn't that large. There are different
metallicities, and also Tau Ceti is a single star, so there is a
different history.

In this case, both are main-sequence stars. However, the spectral type
itself says little about the mass; red giants and red dwarfs, for
example, can have the same spectral class (but different luminosity
classes).
 




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