Total radiation flux from a star

[Radu094]

Hi all !

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/m2 of the star, but also the expected high-energy radiation, thermal, solar wind pressure.. well, the works.

I understand I can basically use Stefan–Boltzmann (and then reverse square distance for attenuation) to get the W/m2, but I'm more interested in how different fusion processes will create different amounts of ionizing radiation, and specifically how different types of stars will create different types (and amounts) of radiation.

 

[qraal]

Hi all !

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/m2 of the star, but also the expected high-energy radiation, thermal, solar wind pressure.. well, the works.

I understand I can basically use Stefan–Boltzmann (and then reverse square distance for attenuation) to get the W/m2, but I'm more interested in how different fusion processes will create different amounts of ionizing radiation, and specifically how different types of stars will create different types (and amounts) of radiation.

Well for one thing we never see the ionizing radiation produced by nuclear fusion in the core because it's thermalized to the Quasi-Stefan Boltzmann spectrum as we see it emitted from the surface. The ionizing radiation emitted is produced by the Sun's magnetic fields as they throw off particles and explosively release magnetic energy. Not easy to predict.

 

[Radu094]

Hmm...enlightning! So the Stefan Boltzmann should account for most of the radiation coming out from a star?

How about estimating the magnetic field strength? I would assume that depends on the rotation of the star? Is there any current way of determining the rotation of observable stars? Or can we determine (estimate?) a rotation based on the known characteristics of a star? eg. I suppose a neutron star will rotate much faster,etc.

 

[Ken G]

Most of the Sun's ionizing radiation (the stuff that gives us sunburn) is fairly steady with time, the bursts of ionizing radiation associated with solar flares are somewhat infrequent and only important for the big flares. Still, one cannot just use a Planck spectrum at the Sun's surface temperature, because the situation in the ultraviolet is more complicated. I'm not sure if you could do any better than just resort to observations, and there's a wide range of different amounts of UV based on detailed factors about the star (like mass and age). One thing's clear, hotter stars than the Sun have more UV, and cooler stars have less, with the exception of "flare stars" that have a lot of flaring activity (like dMe stars, I'll bet they have even more UV than the Sun despite being much cooler, though I'm not sure about that). Basically, if you want UV, just say the star is either hot or very active, and if you don't, say the star is cool and inactive.

 

[Radu094]

Any way I can realistically quantify this given the specs for a star and a distance?
Something that wouldn't be pure guesswork?

I understand there will be a lot of fudge-factors and unknown constants but the general trend will suffice. Heck, even a general 2D diagram will do. I guess what I am asking is how is this ionizing radiation connected to stellar age, surface temp, mass,etc.

Or are there any resources available with enough observational data that I might try a silly regression algorithm ?