  The nature of the low-lying electronic states in carotenoids has been debated
for decades. We use excitation-dependent transient absorption spectroscopy and
comparison with published results on \b{eta}-carotene to demonstrate that the
so-called S* feature in astaxanthin, echinenone and spheroidenone spectra is
due to an impurity in the sample. Excitation at the absorption band-edge
results in a transient absorption spectrum dominated by the pure S1
photo-induced absorption, with no contribution from impurities (S*). We find
that this S1 absorption resembles the triplet excited-state absorption
spectrum, shifted by ~200meV. To explain this, we suggest that the individual
triplets that make up the dominant triplet-pair (TT) configuration of 2A$_g^-$
contribute strongly to the S1 absorption band. Comparison with recent
literature on molecular polycrystalline films which undergo singlet fission
suggests the shift could be related to the binding energy of the triplet pair
state. These findings have implications for understanding triplet-pair states
in organic semiconductors and the excitation-energy dependence of singlet
fission in carotenoid aggregates and biological systems.
