Check the source where you saw "white dwarf 458" — it might be:
: Games Workshop stopped selling individual digital White Dwarf issues as standalone EPUBs/PDFs around 2020; they are now primarily accessible via the Vault. white dwarf 458 pdf
Up to 50% of white dwarfs show heavy elements in their otherwise pure hydrogen/helium atmospheres. This pollution comes from shredded asteroids or comets. The "458" PDF might include high-resolution UV spectroscopy from or FUSE , revealing calcium, magnesium, or iron absorption lines. Check the source where you saw "white dwarf
The number "458" suggests a sequential catalog entry. Several major white dwarf databases use such numeration: white dwarf 458 pdf