2 Observations

2.1 Sample selection

Firstly all galaxies have been selected to be parent galaxies of historical supernovae. Many host multiple SN events. Second, echoes, if present, would be resolved with high resolution imaging using the Hubble Space Telescope instrumentation, i.e. their angular size would be $\ge {0.1}$ arcsec on the long distance scale (i.e., for a low value of the Hubble's constant). This resulted in a total sample of (North & South) 172 galaxies, 211 supernovae. Due to time, visibility and weather constraints, of these we observed 38 galaxies, hosting 64 supernovae. Furthermore, for some, their distance is already well determined by means of normal Type Ia supernovae and Cepheid variable stars (e.g. NGC 5253, IC 4182), thus they are are already tied to traditional methods of distance determinations and can be used for comparisons between different methods. Priority was given to such galaxies and to galaxies hosting multiple events. In other regards, our resulting sample is unbiassed and representative of the larger sample.

2.2 Observing runs

The data presented in this paper were obtained in three observing runs: one at the 1 m Jacobus Kapteyn Telescope (JKT) in La Palma, Canary Islands, in October 1994 and two with EFOSC, at the 3.6 m Cassegrain telescope at the European Southern Observatory, La Silla, Chile, respectively in March and May 1995 (see Tables 1a and 1b). In all runs B, V and R images were taken for each target. Seventeen galaxies were observed with the 1 m JKT and a further 26 with the 3.6 m telescope of ESO. All galaxies are listed, in order of increasing Right Ascension, in Tables 1a and 1b, respectively for the JKT and the ESO runs. Both tables are structured as follows: the galaxy name (NGC, UGC, IC, M) is given in the first column, Right Ascension and declination follow, then the morphological Type of the galaxy is listed in Col. 4. The supernova(e) is (are) given in the fifth column, followed by their offset with respect to the nucleus of the galaxy (unless otherwise noted); finally host galaxy recession velocity, date of observation, exposure times in B, V and R, respectively, are given (from Col. 8 through 11). In Table 1b a letter "p'' next to the exposure time indicates that polarization measurements were also taken. The polarization results will be presented elsewhere. The B and V bands are in the Johnson system, the R in the Cousins.

  

Table 1: a) ^a All coordinates are from the revised Shapley-Ames catalog, unless otherwise noted (3RC=Third Reference Catalog); ^b galaxy morphological type from the Asiago Catalog; ^c offset of the supernova in respect to the nucleus of the galaxy as given in the Asiago Catalog (units: arcsec); ^d recession velocity from the Asiago Catalog (units: km s^-1); ^e observation date in format year/month/date; ^f number of exposures taken in each band and exposure times in seconds; ^g two different fields were taken in order to observe all supernovae; ^h offset (in arcsec) in respect to a nearby star (Porter 1993). An asterisk next to the galaxy name indicates that no R magnitudes were found in the literature. In these cases to calibrate in R we assumed a V-R appropriate to the morphological type of the galaxy, using the relations given by Buta & Williams (1995; their Table 6 and Fig. 3)

 

Table 1: b) ^a All coordinates are from the revised Shapley-Ames catalog, unless otherwise noted (3RC=Third Reference Catalog); ^b galaxy morphological type from the Asiago Catalog; ^c offset of the supernova in respect to the nucleus of the galaxy as given in the Asiago Catalog (units: arcsec); ^d recession velocity from the Asiago Catalog (units: km s^-1); ^e observation date in format year/month/date; ^f number of exposures taken in each band and exposure times in seconds; the letter "p'' indicates that polarimetry was done; ^g lost one exposure and then repeated; ^h offset (in arcsec) in respect to a nearby star (Porter 1993); ⁱ astrometric positions of SNe 1923A and 1957D from Pennington et al. (1982); radio positions of SNe 1950B and 1983N from Weiler et al. (1986). An asterisk next to the galaxy name indicates that no R magnitudes were found in the literature. In these cases to calibrate in R we assumed a V-R appropriate to the morphological type of the galaxy, using the relations given by Buta & Williams (1995; their Table 6 and Fig. 3)

For the JKT observations, only imaging observations were performed. A TeK4 CCD detector was used. This is a high-resolution chip with $\rm {1024} \times {1024}$ pixels corresponding to a $\rm {0.33}~ arcsec ~pixel^{-1}$ image scale. The CCD was used with a gain corresponding to $\rm {0.78}$ electrons per CCD analog-to-digital unit (adu), and the readout noise estimated from the variance of intensity values in the overscan region was measured to be $\rm \sim {4.7}$ electrons. Seeing was measured to be $\sim 1\hbox{$.\!\!^{\prime\prime}$}5$ FWHM typically. Bias (zero-exposures) and flat field frames were taken at the beginning and end of each observing night.

For the ESO observations, both imaging and imaging polarization observations were obtained. We mounted four optical-quality polarizing filters utilizing HN38 Polaroid and anti-reflection coated $\rm Mg{F_2}$ substrates at position angles $\rm 0^\circ$ $\rm {45}^\circ$ $\rm {90}^\circ$$\rm {135}^\circ$ in the first filter wheel to be encountered by the light beam after passing through the aperture plate. The ESO CCD No. 26 was used as the detector. This is a high resolution TeK detector with $\rm {512} \times {512}$ pixels corresponding to a $\rm {0.61} ~arcsec ~pixel^{-1}$ image scale. The CCD was used with a gain corresponding to $\rm {3.8}$ electrons per CCD adu, and the readout noise estimated from the variance of intensity values in the overscan region was measured to be $\rm \sim {8.1}$ electrons. The CCD saturates at $\rm \sim {30~000}$ electrons. Seeing was measured to be $\sim 2''$ FWHM typically. Bias frames were taken at the beginning and end of each observing night and flat field exposures of the dome interior were also obtained.