What happens when Superman goes near other types of stars like white dwarfs?
Superman LOVES white dwarfs! Especially when they're all furry.
OT, the effects of other suns on Superman has changed over the years (hence references to solar suits and blue stars=more power, etc.). Travelling at warp speeds, a Starfleet ship could get close to a yellow star to power up their token Kryptonian fairly quickly. There's also probably some way to recalibrate or modify the radiometric tranformer to emit a high-level microburst of solar readiation in the proper spectrograhic range, or some such technobabble.
A Kryptonian on your ship would be a huge tactical advantage for all the reasons that Superman is super.