Arcturus

Arcturus is a red sun that has Maaldoria, also known as Slaver's Moon, in it's orbit.

History
Supergirl and Mon-El visited Maaldoria by accident when trying to find kidnap victims who turned out to have been abducted by alien slave traders. Due to Arcturus being a red sun, the duo lost their powers while on the world before Alex Danvers exploded a yellow sun grenade giving both of them their powers temporarily while on Maaldoria.