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For refcode 1996MNRAS.278..111P:
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Copyright by Royal Astronomical Society. 1996MNRAS.278..111P The type Ia supernova 1994D in NGC 4526: the early phases F. Patat, S. Benetti, E. Cappellaro, I. J. Danziger, M. Della Valle, P. A. Mazzali, and M. Turatto ESO, Karl-Schwarrschild Strasse 2, D-85748 Garching bei Munchen, Germany ESO, Alonso de Cordova 3107 Vitacura, Casilla 10001, Santiago 19 Chile Dipartimento di Astronomia, Universita di Padova, vicolo dell'Osservatorio 5, I-35122 Padova, Italy Osservatorio Astronomico, Via dell'Osservatorio 5, I-35122 Padova, Italy Osservatorio Astronomico, Via G.B. Tiepolo, 11, I-34131 Trieste, Italy Accepted 1995 July 26. Received 1995 July 12; in original form 1995 March 24 ABSTRACT The type Ia supernova SN 1994D in NGC 4526 was extensively observed as a target of opportunity at ESO. In this paper, we present and discuss the UBVRI photometry and the spectra collected during this campaign from 11 days before maximum to about two months afterwards. Several absorption components of the Na I D lines arising in our Galaxy, in NGC 4526 and in high-velocity clouds located in between have been identified in a high-resolution spectrum. The total amount of reddening related to these features has been estimated as E(B - V) = 0.06. The light curve shapes are similar, but not identical, to those of SN 1992A. The onset of the secondary maximum in the J band occurs around day + 20. The SN reached at maximum B = 11.84 and showed a distinctly blue colour [(B- V)= -0.08]. 5N 1994D is therefore the bluest SN Ia observed to date. SN 1994D appears to depart from the previously reported correlation between maximum brightness and rate of decay. The implications of this for the absolute magnitudes and colour dispersion of type Ia SNe are discussed. The spectroscopic evolution of SN 1994D followed that of standard objects like SN 1992A. The excellent time coverage allowed us to show a sudden break in the decline rate of the expansion velocity deduced from the Si II {lambda}6355 line at around day -6, probably indicating that after this phase this strong feature originates well above the photosphere. Finally, physical parameters and line identifications have been obtained modelling the day - 4 spectrum by means of a spectrum synthesis code. Overall, the spectrum is successfully fitted as a normal SN Ia, although the very blue colour cannot be reproduced. The observed weakness of the Co II absorption around 3350 A and its possible bearing on the amount of radioactive Ni produced during the explosion are discussed. Key words: supernovae: general - supernovae: individual: SN 1994D - supernova remnants.
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