I thought I would outline a bit about what a dilaton is, along with the other scalar field the axion. The graviton on the closed string has two directions of oscillation, x and y. These correspond to the creation and annihilation operators
a^μ_n, (a^μ_n)^† --- > x-direction
b^μ_n, (b^μ_n)^† --- > y-direction
and we can construct a general spin or m = 1 polarization state with (a^μ_n)^† + i(b^μ_n)^†, and a m = -1 state with (a^μ_n)^† - i(b^μ_n)^†. This polarization pertains to the string parameter space. This is not the graviton state, but the composition of two of these with mode matching n and -n, due to Noether's theorem for equal left and right moving quanta, such as
((a^μ_n)^† + i(b^μ_n)^†)((a^ν_{-n})^† + i(b^ν_{-n})^†),
gives a spin 2 field corresponding to a curvature.
The graviton is massless. This means that a spin = 2 boson can't be placed in a reference frame where the projection of that spin onto the momentum vector is zero. In other words the graviton can't be put in a frame where where the particle is at rest. The same holds for the photon. However, with the graviton I can compose the two polarization states into a field
((a^μ_n)^† + i(b^μ_n)^†)((a^ν_{-n})^† - i(b^ν_{-n})^†),
which as a composition of m = 1 and m = -1 polarization states means this has a spin of zero. This particle state is a scalar state and is the dilaton field. The other field with spin = 0
((a^μ_n)^† - i(b^μ_n)^†)((a^ν_{-n})^† + i(b^ν_{-n})^†),
is the axion field. The axion field is involved with the CP symmetry of the strong interaction.
It is possible to construct a spin = 1 particle state. For the entire bulk in 10 dimensions there can be other dimensions beyond μ = 0, 1, 2, 3, there are others a = 5, 6, 7, 8, 9, 10. So we can have a graviton of the form
((a^μ_n)^† + i(b^μ_n)^†)((a^5_{-n})^† + i(b^5_{-n})^†).
If we curl up that fifth dimension in a Calabi-Yau space (say a circle if we consider only this additional dimension) the closed string becomes an open string with the raising and lower operators (a^μ_n)^† + i(b^μ_n)^† and a^μ_n + ib^μ_n, and this funny operator for this internal space, which in the case of only one additional fifth dimension is a photon or a gauge vector boson
