Was SN 1961V a Genuine Supernova?

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Session 19 -- Supernovae and SNRs
Oral presentation, Monday, 2:30-4:00, Zellerbach Auditorium Room

[19.03] Was SN 1961V a Genuine Supernova?

G.C.Bower, A.V.Filippenko, L.C.Ho, G.S.Stringfellow (UCB), R.W.Goodrich (Caltech), A.C.Porter (NOAO)

Analysis of new and old ground-based observations led Goodrich et al. (1989, ApJ, 342, 908) to postulate that the unique Type V (or peculiar Type II) supernova 1961V in NGC 1058 was not a genuine supernova (the explosion of a massive star at the end of its life). Instead, it was the super-outburst of a luminous blue variable --- an exaggerated $\eta$ Carinae-type outburst of a very massive, evolved star near the end of core hydrogen burning. The long plateau in the light curve following outburst, at nearly the same brightness as the pre-outburst star, suggests that the progenitor survived the outburst and was seen for more than four years afterward. It eventually faded only because of the formation of optically thick dust in the ejecta. Goodrich et al. (1989) predicted that the present visual brightness of the star should be near 27 mag, but possibly as bright as 23 mag if the wind phase is still active.

To test this hypothesis, we have obtained $V$, $R$, and $I$ CCD images of the site of SN 1961V with the Wide Field Camera aboard the Hubble Space Telescope. We find a cluster of faint ($V \approx 24$ mag), blue stars around the general location of the supernova, consistent with the detection of an H~II region in the ground-based spectra. We also see a very faint ($V \approx 25$ mag), much redder (in $V-I$) star barely resolved from one of the blue stars. To within the accuracy of the HST absolute coordinates ($\sim 0.5-1$ arcsec), the red star is coincident with the known position of SN 1961V. Moreover, it is anomalously bright in $R$, consistent with the presence of broad H$\alpha$ emission at the position of SN 1961V in the long-slit, ground-based spectrum.

Thus, we believe that we have identified the ``progenitor'' of SN 1961V thirty years after outburst; it is now a very red star due to an envelope of dust. SN 1961V was therefore probably not a genuine supernova. Optical HST images having considerably higher signal-to-noise ratios, infrared images, and superior spectra showing the object's continuum are needed to verify our conclusion.

This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by AURA, Inc., under NASA contract NAS5-26555. Financial support was provided by NASA through Grant GO-2590.01-87A from STScI.

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