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THE TYPE la SUPERNOVA 1986G IN NGC 5128: OPTICAL PHOTOMETRY AND SPECTRA

M. M. PHILLIPS, A. C. PHILLIPS, S. R. HEATHCOTE, V. M. BLANCO, D. GEISLER, D. HAMILTON, N. B. SUNTZEFF, F. J. JABLONSKI, J. E. STEINER, A. P. COWLEY, P. SCHMIDTKE, S. WYCKOFF, J. B. HUTCHINGS, J. TONRY, M. A. STRAUSS, J. R. THORSTENSEN, W. HONEY, J. MAZA, M. T. RUIZ, A. U. LANDOLT, A. UOMOTO, R. M. RICH, J. E. GRINDLAY, H. COHN, H. A. SMITH, J. H. LUTZ, R. J. LAVERY and A. SAHA
Publications of the Astronomical Society of the Pacific
Vol. 99, No. 617 (July 1987), pp. 592-605
Stable URL: http://www.jstor.org/stable/40678969
Page Count: 14
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
THE TYPE la SUPERNOVA 1986G IN NGC 5128: OPTICAL PHOTOMETRY AND SPECTRA
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Abstract

Optical light curves and spectra of the Type la supernova 1986G in NGC 5128 (Centaurus A) are presented. SN 1986G was discovered approximately one week before maximum light. The initial rate of decline of the B light curve was remarkably fast and characteristic of the infrequently observed Pskovskii photometric class β = 12. Although the spectral evolution closely resembled that of the more common "slower" photometric classes of Type Ia supernovae, subtle differences in the maximum-light spectra were detected. The expansion velocity of the photosphere of SN 1986G decreased rapidly at early phases, suggesting that the outer-envelope density gradient was less steep than in supernovae with smaller values of β. SN 1986G appears to have been heavily obscured (E(B -V) = 0.90 ± 0.10) by the dust lane of NGC 5128. This circumstance accounts for the strong interstellar-absorption lines of Ca II H and K and Na ID observed in the spectra as well as for several weaker absorption features that we identify with the diffuse interstellar bands. SN 1986G provides graphic confirmation of the existence of intrinsic differences in the optical light curves and spectroscopic properties of Type la supernovae. Consequently, these objects must be used with considerable caution as cosmological standard candles. On the basis of the very close resemblance of SN 1986G to SN 1971 I in NGC 5055, we derive a relative distance of D NGC 5128 /D NGC 5055 = 0.39 ± 0.04. Further distance estimates are hampered due to the lack of other well-observed Type la supernovae with β = 12.

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