If you're spellcasting in a non-magical aura (lets say a faerie aura) but it happens in calm unstressed conditions, can you do so with a simple die (as spellcasting in calm conditions is normally done) and not suffer the chance of the extra botch dice from the aura.
The rule stating a simple die for spellcasting in calm conditions is found in page 81, while the rule stating extra botch dice for aura is found in page 183 of the ars magica 5 rulebook.
Read on on page 81. "in a calm situation there are no botch dice, even if the maga is in a strange aura"
I'd say yes, but you still suffer the realm penalty to your casting total.
You took that quote out of context, the complete sentence says:
"If the maga has mastered the spell, the die is always a stress die, but in a calm situation there are no botch dice, even if the maga is in a strange aura"
There are two possible interpretations of that sentense
Interpretation 1: The sentense deals only with mastered formulaic magic, which is not the case here, so the sentence can be ignored completely
Interpretation 2: Why is it necessary to specify that there are no botch dice in a calm situation even in a strange aura, unless there would have been botch dice, had the spell not been mastered
I should have stated that we were dealing with formularic spellcasting of a non-mastered spell...
Non-mastered formulaic spells cast in calm conditions are not stress rolls and thus do not incur botches. The rule is there to indicate that switching to stress rolls without risk of botch is a bonus that comes with mastery.
You reroll on a one, but do not check for botches at all on a zero, even though "ordinary" stress rolls require you to account for botch dice from the aura and the like. In ArM4, you had the "quality die" (rerolled on a one, zero is ten, no botches), but it has been removed in ArM5, to simplify the rules, I guess.
As a flavour as opposed to rules issue, a strange Aura is precisely that...strange.
I'd always say that you gain no more botch dice then 1 basic plus aura, unless the spell was mastered when it would be reduced by the mastery level (and gold cord and cautious sorceror etc).
The reason for this is that i'd say different quirks of the aura could catch a magus off guard and skew his magic accordingly.