Yes, this star could certainly have been an angel. It also could have been the Shekina [sic?] Glory of the Lord. It is also possible that it was a star in the normal sense that was supernaturally moved and placed. Whatever the nature of the star, it certainly was an unusual event created by God for specifically this event.
It definitely wasn't St. Elmo's fire, because he wasn't cannonized until years later. ;)
BTW, good use of commentaries!
Luke 2:4 And Joseph also went up from Galilee, out of the city of Nazareth, into Judaea, unto the city of David, which is called Bethlehem; (because he was of the house and lineage of David)
My 8-year-old perceives that it was a star of David.