Emission line core in sunspots

[spossatamente]

What makes the core of some chromospheric lines such as the transition at 8542 A of the infrared Ca II triplet appear in emission in the dark umbra of sunspots?

 

[andrew s 1905]

The emission is from the chromosphere and can be seen in contrast against the strong absorption from the cooler photosphere of the spot.

A similar thing is now happening in Rho Cas where emission from a shell of material is showing in emission within some absorption lines as the stars photosphere cools.

Regards Andrew

 

[andrew s 1905]

In addition there is enhanced chromospheric heating above the sunspots due to the concentration of magnetic flux enhancing the emission.
Regards Andrew