As to what species in particular, I can only readily identify the showiest of them all, the New England Aster, shown here:
In the same field I found this specimen...
... and this one that is similar, but obviously not the same.
In our woods we have lots of these, which I believe to be White Wood Aster.
It seems to change color from white and yellow to pink and purple with age.
If anyone out there knows of a good guide to asters, I'd love to hear about it!