What do I do as a person who davens ashkenaz when I am in a Sefardi shul for tachanun? Should I do what they doing? Or what my Minhag is? If I do what my minhag is should I say the י״ג מידות with them??
R’ S. >Z Auerbach zt”l said that when a eperson davens in a minyan that is differant that his minhag, whatever is said out loud, like kiddusha, etc. he should say like the shul. However the parts that are said quietly, such as Shemona Esrei, that he can say like his personal minhag. Therefore you should say the י״ג מידות with them.