Disc of quiet and active Proxima

[snorkack]

TL;DR Summary

Looks of Proxima Centauri as viewed from Proxima b

The radius of Proxima is quoted as 0,1542 solar.
The distance of Proxima b is quoted as 0,04857 AU.
It follows that the angular size of Proxima from b is 3,175 times angular size of Sun from Earth, plus correction to small angle approximation. Since Sun averages 32 minutes, Proxima is about 102 minutes from b.

The angular area of Proxima from b is about 10,1 times that of Sun.
Bolometric luminosity of Proxima is about 1,7 thousandths of Sun, and thus b gets about 72 % of bolometric heating of Earth. Therefore the bolometric surface brightness of quiet Proxima is 14 times smaller than that of Sun.

Visual luminosity of quiet Proxima is 49,2 millionth of Sun, and thus b gets about 2,1% illumination of Earth. Therefore the visual surface brightness of quiet Proxima is 500 times smaller than that of Sun.

Proxima, however, has been observed to flare to 65 times its quiet visual brightness.
Is this isotropic? When Proxima flares, does the whole sphere, thus the whole disc, brighten simultaneously and uniformly?

If not, what are the flares like?

Does the colour index of Proxima remain constant in flares?
How does the surface luminosity and colour index of flares compare to quiet Proxima? To Sun?
What is the shape of a flare? Round, or different?

When a flare is seen against the limb of Proxima, does the limb stay circular?
Also, what are reasonable estimates for radius of Proxima d?

 

[lippyka]

It is not possible to accurately estimate the radius of Proxima d without more information. However, it is likely to be much smaller than Proxima b due to its distance and the fact that it is a failed star, or brown dwarf. Depending on its mass and composition, it could have a radius anywhere between 0.1 and 0.3 solar radii.