  Transits of exoplanets observed in the near-UV have been used to study the
scattering properties of their atmospheres and possible star-planet
interactions. We observed the primary transits of 15 exoplanets (CoRoT-1b,
GJ436b, HAT-P-1b, HAT-P-13b, HAT-P-16b, HAT-P-22b, TrES-2b, TrES-4b, WASP-1b,
WASP-12b, WASP-33b, WASP-36b, WASP-44b, WASP-48b, and WASP-77Ab) in the near-UV
and several optical photometric bands to update their planetary parameters,
ephemerides, search for a wavelength dependence in their transit depths to
constrain their atmospheres, and determine if asymmetries are visible in their
light curves. Here we present the first ground-based near-UV light curves for
12 of the targets (CoRoT-1b, GJ436b, HAT-P-1b, HAT-P-13b, HAT-P-22b, TrES-2b,
TrES-4b, WASP-1b, WASP-33b, WASP-36b, WASP-48b, and WASP-77Ab). We find that
none of the near-UV transits exhibit any non-spherical asymmetries, this result
is consistent with recent theoretical predictions by Ben-Jaffel et al. and
Turner et al. The multi-wavelength photometry indicates a constant transit
depth from near-UV to optical wavelengths in 10 targets (suggestive of clouds),
and a varying transit depth with wavelength in 5 targets (hinting at Rayleigh
or aerosol scattering in their atmospheres). We also present the first
detection of a smaller near-UV transit depth than that measured in the optical
in WASP-1b and a possible opacity source that can cause such radius variations
is currently unknown. WASP-36b also exhibits a smaller near-UV transit depth at
2.6$\sigma$. Further observations are encouraged to confirm the transit depth
variations seen in this study.
