[Avodah] Rav Moshe Shternbuch: Do Adopted Children Sit ShivaFor Their Step Parents?

[Poppers, Michael]

> From http://revach.net/article.php?id=1529 <
A timely post, given the beginning of P'Emor. 

> He adds that this is a Mitzva not a Chiyuv. <
A Kohein can be m'tamei for his q'rovim (presumably, if he's adopted, he cannot be m'tamei for the parents who adopted him, much less for their biological children) -- is he m'chuyav to?

Separate but related Q: precisely what aspects of shiv'a _are_ considered a chiyuv rather than a "mitzva" or widespread minhag?  The chiyuv q'riyah (again, something I imagine RMS would at least say is not a chiyuv for an adopted child and may say he cannot perform [am I allowed to tear my clothing for a dear uncle or grandparent?]) occurs prior to shiv'a, so it's not part of the Q.  Thanks. 

All the best from 
-- Michael Poppers via BB pager