2 Observations and data reduction

The sample presented in this paper is a part of a sample of starburst galaxies selected from the Markarian catalog. Galaxies with m_v brighter than $14\hbox{$.\!\!^{\rm m}$}5$ and angular sizes greater than 30$^{\prime\prime}$ were selected. No consideration was made for any particular morphological type and the sample is unbiased towards the morphology of the galaxy. In this paper, results based on the photometric studies of ten galaxies from the sample are presented. These ten galaxies are listed in Table 1, along with their coordinates, morphological types, distances (H₀ = 75 km s^-1 Mpc^-1 has been adopted throughout), total exposure times in each band, the derived ellipticity, inclination and position angle.

The observations were made at the Cassegrain focus of the 1.2 m Gurushikhar telescope employing a thinned back illuminated Tektronix 1024$\times$1024 CCD chip. The observations were carried out under photometric conditions with typical seeing of 1.5$^{\prime\prime}$. Binning of 2$\times$2 was employed before recording the images to increase the signal-to-noise ratio of the measurements and keeping in mind the data storage requirements. The final resolution was $0\hbox{$.\!\!^{\prime\prime}$}634$/pixel which is sufficient to sample the PSF appropriately. The field of view provided by the chip was 5$\hbox{$.\mkern-4mu^\prime$}2\times$5$\hbox{$.\mkern-4mu^\prime$}$2. Broad band Johnson's B and V and Kron-Cousin's R and I filters were used. About 3-4 exposures were taken in each of the photometric bands. The galaxy Mrk 87 was observed during two runs as the signal in the B band was found to be inadequate after the first observing run. Twilight flats were taken and median filtered to construct the master flats. The data was reduced using IRAF on the IBM-6000 RISC system at PRL, Ahmedabad. Standard procedures of bias subtraction, flat-fielding and cosmic ray removal were done on the raw images. For the photometric calibrations of the BVRI images, stars from Landolt ([1992]) were observed. The photometry of the standard stars was carried out using the DAOPHOT task in IRAF. Twenty standard stars from Landolt having $8\hbox{$.\!\!^{\rm m}$}0 < V< 15\hbox{$.\!\!^{\rm m}$}0$ and -0.20<B-V< +1.00 were observed. Instrumental magnitudes were converted to standard magnitudes using the following equations obtained after a least squares fitting.

$$\begin{eqnarray} (B-V) & =& (b-v)-0.48 \nonumber\\ (V-R) &=& 1.05(v-r)-0.18+0.05(B-V) \nonumber\\ (R-I) &=& 0.94(r-i)+0.36+0.04(V-R) \nonumber\end{eqnarray}$$

where lower cases denote instrumental values and upper cases correspond to the standard values. All the magnitudes and colours presented in this paper are in the B and V Johnson's and R and I Kron Cousin's system which is similar to the one used by Landolt to obtain the magnitudes and colours for the standard stars in his catalogue. Corrections for airmass were applied using the coefficients obtained from the transformation equations. The typical errors in the transformed magnitudes are 0.03 in B, 0.03 in V, 0.02 in R and 0.04 in I. The galaxy images were shifted and co-added to improve the signal-to-noise ratio. The sky background was computed from the mode of the histogram of the image. The field of view was large enough compared to the program galaxies so that the histograms were sky dominated. The galaxy images were sky subtracted and subsequently scaled for 1 second exposure.