# Total radiation flux from a star

I'm looking around the net to find good resources on how to compute total radiation flux from a given star at a given orbiting distance.

Ideally I'd like to get not just the $W/m^2$ of the star, but also the expected high-energy particles, EM, thermal, solar wind pressure.. well, the works.

Everywhere I looked they seem to compute these values for our Sun and at 1AU, then I'm left to wonder how this relates to stellar mass, composition type, luminosity, distances, etc.

In the end, I'm trying to quantify a sort of habitability range around a given star. Much in the way of saying: well, given this blue-hypergiant you could get close to about $40$ $AU$ before you get toasted in your puny spacecraft. Or, habitable planets could exist between $100$ AU and $120$ AU.etc..

I would have thought this would have been more common around sf projects, but radiation seems to go unnoticed in most sf themes.

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## 2 Answers

Stars are (ironically) pretty good approximations to black bodies, so if you know their surface temperature and surface area you can calculate the radiation emitted using the Stefan-Boltzmann law.

This only applies to electromagnetic radiation. I don't know how you'd calculate the intensity of the stellar wind. However whether you'd get toasted or not is mainly down to the EM radiation.

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To get the expected level of stellar wind, would depend strongly on what kind of a star it has. For example the "wind" around a pulsar is significantly different to the sun, which would be significantly different to a hotter/colder star. This boils down to the differences in emission, or rather at what electromagnetic frequencies the peak emission occurs.

The amount of wind will also depend on the magnetic field of the star in question, which is again a model dependent thing. So unless you have a model for the type of star involved, I don't think you can get very reliable numbers on this.

But as John Rennie points out (answer to the same question), given the surface temperature of a star, one could calculate the radiation emitted. That will give you a fairly good estimate of how 'toasted' you'll be near a star, since stellar winds are usually plasma, which will kill you if they could get to you, but assuming you're protected they won't change the temperature of your surroundings too much.

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