A New Faint Type I[CLC]a[/CLC] Supernova: SN 1997[CLC]cn[/CLC] in NGC 5490

Observations of the recent SN 1991bg in the elliptical galaxy NGC 5490 showthat this objects closely resembles, both photometrically andspectroscopically, the faint SNIa 1991bg. The two objects have similar light curves, which do not show secondary maximain the near IR as normal type Ia supernovae. The host galaxy, NGC5490, lies inthe Hubble flow. Adopting for SN1997cn a reddening E(B-V)=0, the absolutemagnitude is faint: MV = -17.98 using Ho=65 and MV = -17.40 using Ho=85 km/(sMpc). The latter value is in close agreement with the absolute magnitude of SN1991bg on the SBF--PNLF--TF distance scale. The photospheric spectra of the twoSNe show the same peculiarities, the deep TiII trough between 4000 and 4500A,the strong CaII IR triplet, the narrow absorption at about 5700A and the slowexpansion velocity. In analogy to SN 1991bg the observed spectrum of SN1997cnhas been successfully modeled by scaling down the W7 model by a factor of 2,assuming a rise time to B maximum of 18 days, a photospheric velocity and aneffective temperature low compared to normal SNIa. The influence of thedistance scale adopted on the input parameters of the best fit model is alsodiscussed. These data demonstrate that peculiar SNIa like SN 1991bg are notonce--in--a--lifetime events and that deep SN searches can be contaminated byunderluminous SN Ia in a fairly large volume.Comment: accepted for Astron.; J. 6 figure