Hi Suzy & all,
Quote:
Originally Posted by Suzy
Interesting Rob  , I've been wondering why E.Carina shows up yellow where as infact it is a LBV. |
The LBV phenomenon is currently believed to be an evolutionary stage most if not all really massive stars (ie >70-odd solar-masses) pass through -- the "B" part here can be a bit midleading because they're not always blue and their spectrum is in a state of frequent flux as is their colour/temprature. They sometimes show A and F type spectra and also the rare Ofpe/WN9type spectral type. These unstable stars are shedding mass at very high rates and are almost always surrounded by small planetary-type nebulae that have been ejected in outbursts over a period (like the Homunculus surrounding Eta Carinae).
It is a stage these super-stars pass through to loose mass and their outer-layers before they end up as stripped-down Wolf-Rayet stars which ultimately expire either as Type Ib or Ic (stripped-core collapse) "collapsar" supernovae.
These two types of supernovae (particularly Ic) are thought to produce the deadly, highly focused bi-polar "long" gamma-ray bursts that originate when the core collapses directly to a singularity. If one of these bad-boys goes off <100,000ly away and is pointing it pole
exactly at you; find somewhere quiet to lie down, say your prayers and put a paper-bag over your head -- you're cooked.
Sometimes as LBVs they don't/can't hang around long enough to eject their outer envelopes of Hydrogen and Helium to become Wolf-Rayets and instead undergo core-collapse to become Type II supernovae, or as another alternative possibly end as an exotic pair-instability supernova that disrupts the entire star. This last scenario is only reserved for the absolute top-shelf mega-boys (ie >120 solar-masses) that leaves behind no remnant (ie no neutron star/singularity).
It looks a bit like heavy-going, but there is a good, meaty explanation about the LBV evolutionary stage here:
http://www.peripatus.gen.nz/Astronomy/LumBluVar.html
as a matter of pure trivia, it mentions the LBV hypergiant AG Carinae (which has the exotic Ofpe/WN9 type spectra) quite a bit. I've a soft-spot for this star as it is (when in outburst) the most distant naked-eye star in our sky at almost 20,000ly. To put that in context, the overwhelming majority (probably > 95%) of naked-eye stars are closer to the Sun than 2,000ly.
Hope it helps.
Best,
Les D
