SN 1998bp in NGC 6495

(vsnet-alert 1736)

Dear all,

Yet another (potentially) bright SN has been discovered. Because the peculiarity is reported, it is worth monitoring further!

Acoording to IAUC 6890 and 6891, SN 1998bp has been discovered by English amateur astronomer M. Armstrong on Apr. 29.074. The location of the new star is R.A. = 17h54m50s.71, Decl. = +18o19'49".3 (2000.0), which coincidents to about 15" north from the center of the host galaxy NGC 6495. Another astrometry given by A. Sugie, Dynic Astronomical Observatory, shows that the end figures of the position is 50s.72, 50".2. Reported CCD magnitudes are: Mar. 20.283, >16.7: Apr. 29.074, 14.8: 29.135, 14.7: 30.54, 14.9-15.1(V).

Spectroscopy has performed by ESO group and Harvard group: they report that SN 1998bp is of type Ia around the maximum, but peculiar. ESO group mentioned that 635 nm (at rest) Si II feature is weak and many lines show P-Cyg profile. The color is rather red than normal SNe Ia, despite it seems not be reddened by scattering. Harvard group mentioned that the ratio of the deepness of Si II features (615 nm and 580 nm), which is thought to be an indicator of the intrinsic brightness of SNe Ia, is nearly equal to that of sub-luminous SN Ia 1991bg. However, the bluer region of the spectrum of SN 1998bp does not resemble that of 1991bg.

The host galaxy NGC 6495 is a elliptical one. Its recession velocity is estimated by ESO group and catalogued in some references.

CfA-redshift     3208 km s-1
Di Nella et al.  3127         (A.Ap.Suppl, 113, 151 (1995))
ESO group        4500

These three indicate that NGC 6495 is not so near as Virgo cluster; it looks like about three or four times further than Virgo. Typical SNe Ia at this distance would expected to glow at 14.5-15.0 mag on maximum. Compared with the reported magnitudes, it is not likely that SN 1998bp is especially sub-luminous as 1991bg, as Dr. Taichi Kato noted.

Followup photometry and spectroscopy is strongly encouraged. Particularly, because the decline rate after the maximum is thought to be another indicator of the luminosities of SNeIa, it is very important to develop the light curve.

Sincerely Yours,
Hitoshi Yamaoka, Kyushu Univ., Japan

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