No. Aasimar is not a celestial in 5e. They look like people.Even though they come from a celestial being or have been blessed by one, aasimar still looks like a human. That's it for D&D 5e's celestial creatures. They are one type of monster that makes up the different creatures in your game. They are great allies or enemies because they naturally show how they are aligned. But there aren't that many official celestial creatures, and the conjure celestial spell gives you even less choice. Last thing: if you want more celestial creatures, just change the creature type of another monster. Nothing is stopping a dungeon master from taking a goblin and saying, "This is now a celestial creature." Not even a thing. As a DM, that's your right.