  The invariant subalgebra H^+ of the Heisenberg vertex algebra H under its
automorphism group Z/2Z was shown by Dong-Nagatomo to be a W-algebra of type
W(2,4). Similarly, the rank n Heisenberg vertex algebra H(n) has the orthogonal
group O(n) as its automorphism group, and we conjecture that H(n)^{O(n)} is a
W-algebra of type W(2,4,6,...,n^2+3n). We prove our conjecture for n=2 and n=3,
and we show that this conjecture implies that H(n)^G is strongly finitely
generated for any reductive group G\subset O(n).
