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Observations and reduction

Long-slit spectra in the range 3600-8000 ÅÅ were obtained during three runs. The spectra were centered on a star-like object at $\approx 3\arcsec$ to the west and $\approx 4\arcsec$ to the south of the galaxy center. The spectrograph SP-124 at the Nasmyth-1 focus of the 6 m telescope with UAGS camera and Photometrix CCD PM1024 ( $24\times24$$\mu$m pixel size) was used for the observations. The spatial scale along the slit was equal to $0.4\arcsec$/pixel, the slit length was about $40\arcsec$, and a slit width of $2\arcsec$ was used. Gratings with 300 and 600 grooves/mm were used, resulting in a spectral resolution of approximately 12 and 6 Å (FWHM). Series of bias images were obtained twice -- at the beginning and at the end of every night. Dark current and flat field were usually accumulated at the end of the night. At least two standard stars from the list of spectrophotometric standards (Massey and Strobel, 1988) were observed every night. A He-Ne-Ar lamp was used for wavelength calibration.

 

Table 1: Dates and instrumentation set-up for spectroscopic observations

Date (UT)	April 6.914	April 19.774	April 24.783
	1998	1998	1998
Dispers.	2.4	2.4	4.6
(Å/pixel)
Resol. (Å)	6	6	12
Spectr. range	3700-6100	3700-7400	3600-8000
(ÅÅ)
Expos. time	300	300	600
(s)

In Table1 the instrumental set-ups are presented for spectral observations of SN1998bv and the galaxy HS1035+4758. The spectroscopic data were reduced using the context LONG from the MIDAS software package. The reduction of the original two-dimensional CCD data included the standard steps such as bias and dark subtraction, flat-fielding, cosmic-ray removal. After wavelength mapping, the night sky background subtraction was performed. 1D spectra were extracted by adding some consecutive CCD rows centered on the object intensity peak along the slit. Then corrections for atmospheric extinction and flux calibration were applied. For the flux calibration we used the mean response curve obtained from the observations of standard stars.