We present spectroscopic and photometric observations of the peculiar Type II supernova ( SN ) 1998A .
The light curves and spectra closely resemble those of SN 1987A , suggesting that the SN 1998A progenitor exploded when it was a compact blue supergiant .
However , the comparison with SN 1987A also highlights some important differences : SN 1998A is more luminous and the spectra show bluer continua and larger expansion velocities at all epochs .
These observational properties indicate that the explosion of SN 1998A is more energetic than SN 1987A and more typical of SNe II .
Comparing the observational data to simulations , we deduce that the progenitor of SN 1998A was a massive star ( \sim 25 M _ { \odot } ) with a small pre–supernova radius ( \la 6 \times 10 ^ { 12 } cm ) .
The Ba II lines , unusually strong in SN 1987A and some faint II–P events , are almost normal in the case of SN 1998A , indicating that the temperature plays a key role in determining their strength .