  We compute an extensive set of early-time spectra of supernovae interacting
with circumstellar material using the radiative transfer code CMFGEN. Our
models are applicable to events observed from 1 to a few days after explosion.
Using these models, we constrain the progenitor and explosion properties of a
sample of 17 observed interacting supernovae at early-times. Because massive
stars have strong mass loss, these spectra provide valuable information about
supernova progenitors, such as mass-loss rates, wind velocities, and surface
abundances. We show that these events span a wide range of explosion and
progenitor properties, exhibiting supernova luminosities in the 1e8 to 1e12
Lsun range, temperatures from 10000 to 60000 K, progenitor mass-loss rates from
a few 1e-4 up to 1 Msun/yr, wind velocities from 100 to 800 km/s, and surface
abundances from solar-like to H-depleted. Our results suggest that many
progenitors of supernovae interacting with circumstellar material have
significantly increased mass-loss before explosion compared to what massive
stars show during the rest of their lifetimes. We also infer a lack of
correlation between surface abundances and mass-loss rates. This may point to
the pre-explosion mass-loss mechanism being independent of stellar mass. We
find that the majority of these events have CNO-processed surface abundances.
In the single star scenario this points to a preference towards high-mass RSGs
as progenitors of interacting SNe, while binary evolution could impact this
conclusion. Our models are publicly available and readily applicable to analyze
results from ongoing and future large scale surveys such as the Zwicky
Transient Factory.
