View Full Version : RCW120

2010-May-15, 07:10 AM
How bright, in visible light, is the central star (O8V) of RC120W? And what is its mass?

How long does it take for the massive protostar to reach main sequence? And when it does, how bright shall it be?

Messier Tidy Upper
2010-May-15, 03:55 PM
Meissa or Lambda Orionis is an O8 V (dwarf or main-sequence ie. fusing hydrogen at its core) so RCW120's central star will be similar in brightness to it in absolute terms.

See Kaler's stars Meissa page : http://stars.astro.illinois.edu/sow/meissa.html & for compasrion with other O type stars : http://stars.astro.illinois.edu/sow/class.html with links to the O7.5 V class Regor A and quite a lot of O9 V stars.

From that link Kaler - the expert in this area - notes :

From its distance of 1000 light years, we find the hot, bright component to radiate 65,000 times more energy than our Sun (including its ultraviolet radiation), ... With an immense mass nearly 25 times that of the Sun, explosion is almost certain to be the fate of Meissa's brighter component.

The brighter component there being, I presume, the O8 star - a B0 type companion is also present. Meissa is a third magnitue (medium brightness roughly) star.

I'm not sure how far off the RC120W cluster (?) is so can't guess at how bright it may appear in our sky however I would expect its absolute magnitude (intrinsic brightness rather than apparent mag or how bright we see it) would be very high around minus five or so. (For comparison Venus at its brightest is about mag. minus four and a half.)

Afraid I'm not at all sure how long it will take for this star to reach the main-sequence - can't even venture a guess there, sorry.