We present ALMA Band 6 (1.3 mm) observations of Fomalhaut and its debris
disk. Since the system is relatively close at 7.7 pc, it has been the
target of numerous studies at multiple wavelengths, and can serve as a
test-bed for debris disk evolution models and planet-disk interactions.
Outstanding issues that need to be resolved to properly characterize the
debris include tightening constraints on the spectral index in the
submm/mm regime and determining whether there is indeed excess over the
stellar emission, indicating the presence of an inner debris disk or ring.
These ALMA 1.3 mm observations provide the highest resolution observations
to date of the mm grains the outer ring. Tight constraints are placed on
the geometry of the disk and on the mm-wavelength spectral index. We
explore fitting the debris disk model in the image plane in addition to
the standard method of fitting the visibilities. The results are compared
and potential advantages/disadvantages of each approach are discussed.
The central emission detected is indistinguishable from a point source,
with 0.90 mJy being the best fit flux of the host star for Fomalhaut
itself. This implies that any inner debris component must contribute
little to the total central emission. Moreover, the stellar flux is less
than 70% of that predicted by extrapolating a blackbody from the
constrained photosphere temperature and just over 70% of the flux if
extrapolating from the far infrared. This behavior is similar to that seen
in the Sun for submm/mm wavelengths, but more pronounced. Currently,
insufficient data exists to properly constrain the degree to which stellar
atmospheres affect the observed flux in the submm/mm regime. This result
is part of an ongoing larger project focused on measuring the emission
from stellar atmospheres at submm/mm wavelengths which directly impact
inferred excesses for debris disk studies.