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lpzho
2011-Dec-17, 04:26 AM
Hello,

I've read that Herbig Ae stars can have solar masses more than three times the sun's, but that main sequence stars of that mass are spectral type B. Does that mean the big Herbig Aes will turn blue when they hit the main sequence?

Is the temperature of pre-main-sequence stars generally lower than when they're fusing hydrogen. I've read its roughly the same.

And whats the high-end of a Herbig Ae masswise?

antoniseb
2011-Dec-17, 09:24 AM
Let me start by welcoming you. You are asking a good fairly detailed stellar astronomy question. I have a feeling that the specifics as far as answers go are fuzzy right now. Herbig Ae/Be stars are from 2 to 8 solar masses (roughly). Below 2, and we call the T Tauri stars. Where the mass boundary between an Be and an Ae is I don't know, and there are only a few such stars known that aren't obscured by gas and dust.

My understanding is that the total energy per second being released by one of these things is significantly higher than their main sequence energy, but concerning temperature, that depends on the radius of the outermost opaque surface, and I don't know how that relates to the eventual main-sequence radius.

It is likely that someone more knowledgeable about this specific class of new stars will give a more detailed response later.

PraedSt
2011-Dec-17, 08:09 PM
Welcome to BAUT Ipzho. I'm not an astronomer, so take the following with a pinch of salt.

I presume an Herbig Ae is thought to evolve into an A-type main sequence star, and an Herbig Ae into a B-type. So blue-white and blue respectively.
If you could provide a link to where you read "temperatures are roughly the same", that would great, because right now I can't see how a pre-main sequence star could have a temperature similar to what it will have once it becomes a star.

lpzho
2011-Dec-18, 02:47 AM
Thanks for the replies.


I presume an Herbig Ae is thought to evolve into an A-type main sequence star, and an Herbig Ae into a B-type. So blue-white and blue respectively.
If you could provide a link to where you read "temperatures are roughly the same", that would great, because right now I can't see how a pre-main sequence star could have a temperature similar to what it will have once it becomes a star.


Pardon, I believe I remembered wrong. I probably mistook luminosity for temperature. It seems they maintain their luminosity across the Henyey track to the main sequence but increase in temperature.

I thought the A in Ae meant its current spectral type and not its future. It was at cornell's website here (http://arxiv.org/abs/1105.0759) where it says some HAes have over 3 solar masses, which ought to make it spectral type B in the main sequence stage.

I guess the Henyey tracks answer my question as to color change. Probably should have done more research prior to posting.

PraedSt
2011-Dec-18, 08:05 AM
I thought the A in Ae meant its current spectral type and not its future. It was at cornell's website here (http://arxiv.org/abs/1105.0759) where it says some HAes have over 3 solar masses, which ought to make it spectral type B in the main sequence stage.The A and B do mean current spectral type. As they move along the Henyey track they increase in temperature (get bluer), but usually not enough to jump classifications. So an Ae usually ends up as an A and a Be usually ends up as a B. However, as temperature is continuous and classifications are artificial buckets, I suppose its quite possible for an upper Ae to end up as a lower B.

lpzho
2011-Dec-18, 07:16 PM
Yes, its a continuum. I guess any visible color difference would depend on how early it breaks out of its dust cloud and can be seen, how early you're looking, and how long its time as a PMS star is. That could vary greatly I suppose. A big Ae probably wouldn't be out and about too long.

George
2011-Dec-19, 03:57 AM
You won't see any saturated blue stars since these hotter stars are close to blackbody radiators. The spectral photon flux for these hotter stars will always have a strong flux distrubition for the entire visible spectrum, so a rich blue color will be white-washed with the addition of all the other colors.

Interestingly, after making a Excel spreadsheet for Planck distributions, I kept entering higher and higher temperatures to the point where the spectral energy distribution would match approximately our blue sky distribution. This temperature happens to be about the same temperature as the Sun's core, so if you could simply spread open the outer zones of the Sun, and reduce the intensity somehow to a normal photopic level for the eye, then it would appear very blue. [The 'yellow' surface color of the Sun, BTW, would not distort your blue color view of the core since the photosphere "ain't yeller".]