  The cosmological origin of carbon, the fourth most abundant element in the
Universe, is not well known and matter of heavy debate. We investigate the
behavior of C/O to O/H in order to constrain the production mechanism of
carbon. We measured emission-line intensities in a spectral range from 1600 to
10000 \AA\ on Space Telescope Imaging Spectrograph (STIS) long-slit spectra of
18 starburst galaxies in the local Universe. We determined chemical abundances
through traditional nebular analysis and we used a Markov Chain Monte Carlo
(MCMC) method to determine where our carbon and oxygen abundances lie in the
parameter space. We conclude that our C and O abundance measurements are
sensible. We analyzed the behavior of our sample in the [C/O] vs. [O/H] diagram
with respect to other objects such as DLAs, neutral ISM measurements, and disk
and halo stars, finding that each type of object seems to be located in a
specific region of the diagram. Our sample shows a steeper C/O vs. O/H slope
with respect to other samples, suggesting that massive stars contribute more to
the production of C than N at higher metallicities, only for objects where
massive stars are numerous; otherwise intermediate-mass stars dominate the C
and N production.
