  We present spectroscopic and photometric observations of SN1992ar, the more
distant SN in the Calan/Tololo Survey. We compare its spectrum with those of
nearby Type Ia and Ic SNe and conclude that the latter type is a better match
to SN 1992ar. Using K-corrections based on the spectra of well observed Type Ic
and Ia SNe we compute different possible rest frame light curves of SN 1992ar
and compare them with those of representative SNe of each type observed in the
nearby universe. From the photometry and the spectra, we are able to conclude
that SN 1992ar cannot be matched by any known example of a Type Ia SN. Even
though the data set collected is fairly complete (one spectrum and 10
photometric points), it is not possible to decide whether SN 1992ar was a fast
Type Ic SN, like SN 1994I, or a slow one, like SN 1983V. The absolute V
magnitudes at maximum implied by each of these possibilities are -19.2 and
-20.2, respectively. The latter would make SN 1992ar one of the brightest SNe
on record. SN 1992ar, hence, illustrates the problem of contamination faced by
the high z Type Ia SNe samples whose luminosity distances are used to determine
the cosmological parameters of the Universe. We present observational criteria
to distinguish the two SN types when the SiII 6355 line is redshifted out of
the sensitivity range of typical CCD detectors, and discuss the effect that
these luminous Type Ic SNe would have on the measured cosmological parameters,
if not removed from the High-z Type Ia SN samples.
