West opens met 1♣, 1♦, 1♥, 1♠ or 1NT (15-17) respectively.
Each and every time your partner doubles and East passes.
What is your bid as South?

Partner's double is for take out when he doubles a suit. Only the double of 1NT is for penalties.

West opens 1♣.
Over partner North's double and East's pass, you bid 2♥. Don't forget to jump in this situation, if you have 8-11 HCP! After all, you may bid 1♥ on zero HCP, so partner will pass that bid, unless he has a lot of extra strength for his double (completely different from the situation where he opens 1♣ and you respond 1♥: that response shows 6 HCP or more and is forcing). You must give partner something to hold on to.
By the way, bidding 2♥ is much better than bidding 2♦, since a take-out double in principle shows interest in the majors.

West opens 1♦.
Over partner North's double and East's pass, you bid 2♥ as well, same reasoning as above.

West opens 1♥.
Over partner North's double and East's pass, you bid 1NT. You may bid 3♦ as well, 8-11 HCP with at least four diamonds, but 1NT is more practical. You prefer to play notrumps at a low level above diamonds at the three level (especially since you are not even certain that there is a diamond fit, perhaps partner has only three). You show 6-9 HCP and a heart guard. If partner has extra strength, you are heading towards 3NT.

West opens 1♠.
Over partner North's double and East's pass, you bid 3♥. Perhaps 3♥ sounds like extra length in hearts, but that is not true. A 2♥ bid would show 0-7 HCP, so 3♥ shows 8-11; only four hearts are required. The chance of finding a 4-4 fit in hearts is particularly big here: a player who doubles a major suit for take-out, usually has a four-card suit in the other major (and if not, he has extra strength).

West opens 1NT.
Over partner North's double and East's pass, you pass happily. 1NT is going down a lot. So EW had better run, if they have a fit (which is not very likely, since East has passed the double...).