Tamara - From Hebrew tamar "palm" or "bitter taste". The others interpret it as ficus carica. It is in use since Middle Ages. The form Tamara that comes from Russian is more spread.
Pogosyan - Poghossian, Pogossyan, Poghosyan, Poghosian, Pogosyan, etc., is an Armenian surname.
The Western Armenian equivalent is Boghossyan.