"Sie erscheinen regelmäßig, wenn auch nur einmal jährlich."

Translation: They come out frequently, if only once per year.

[Soglio]

What happened to the auch? Shouldn't this translate ". . . if also only once a year"?

[bl1zl3er]

wenn auch nur = if only
Just different ways to say things in different languages.

[karenskywalker]

I thought this one would be more natural "they come out regularly, even if only once a year". But duolingo just rejected it.