1 Introduction

The term "starburst'' was first coined by Weedman ([1973]) to describe galaxies experiencing episodes of star formation that are too intense to be sustained over the lifetime of the galaxy. These bursts of star formation produce 10⁷-10⁹ $M_\odot$ of OB stars (Balzano [1983]) which are the dominant source of the galaxy's luminosity. Since OB stars emit copiously in the ultraviolet, many starburst galaxies were detected in Markarian et al. ([1979]) survey of uv-excess objects and references therein. These lists form one of the largest databases of optically selected starburst galaxies. Huchra ([1977]) conducted a detailed aperture photometric study of a large number of these galaxies. A spectrophotometric survey was conducted by Balzano ([1983]) wherein she studied the spectra of the nuclear regions in the starburst galaxies. Larson & Tinsley ([1978]) were the first to put forward the idea that "bursts of star formation" could be triggered by tidal forces in interacting galaxies. Combes et al. ([1990]) showed that in the presence of non-axisymmetric potentials like bars or companions, gravitational torques are capable of driving the gas in a galaxy into the central regions. This gas may pile-up at the ILR, if it is present or proceed right up to the nuclear region where it may fragment to form ring-shaped or nuclear starbursts. Interactions may also induce extranuclear starbursts as is seen in the H$\alpha$ imaging study of Garcia-Barreto et al. ([1996]).

Dynamical disturbances experienced by the galaxy are reflected in the morphology of the galaxy in the form of peculiar structures. Tidal tails, bridges, asymmetric outer envelopes are some manifestations of the perturbing processes (Combes [1987] and references therein). These disturbances are possible triggers of the starburst phenomenon. Interactions, mergers and the presence of a bar were proposed as the most likely triggers for the starburst. However, it has been observed that a few starburst galaxies show neither visible signs of disturbances in the form of peculiar morphologies nor the presence of a bar in their direct images. A detailed study of the underlying galaxy is especially important in such cases to probe the cause of the starburst. An inspection of the Markarian sample of starburst galaxies reveals that though the starburst phenomenon is predominantly found in spiral galaxies, it is not confined to spirals alone and the sample contains a large number of S0 and elliptical galaxies, in addition to the ones that show too peculiar a morphology to be classified properly. A morphological study of a sample of starburst galaxies through several spectral bands is expected to help shed some light on the conditions leading to the onset of a starburst and the environment of the underlying galaxies. The general structure of the underlying galaxy can be studied through techniques like ellipse fitting. This technique is especially useful in studying isophotal twists, the presence of bars, rings, shells, etc. in the galaxy. In recent years, studies conducted by Wozniak et al. ([1995]) and Jungwiert et al. ([1997]) on samples of spiral galaxies using this technique have been useful in detecting underlying structures like oval distortions, shells, rings and hitherto undetected bars. This technique can be used to study the starburst galaxies in a similar manner. The fine structure extracted from the isophotal analysis can be interpreted to give valuable information about the underlying galaxy and the nature of the disturbances experienced by it (Kenney et al. [1996]). In the present study, a sample of starburst galaxies was observed in BVRI bands and we present results on ten galaxies.

 

Table 1: Sample of starburst galaxies

• [$^{\mathrm{a}}$] Markarian catalogue (downloaded from CDS).