Photometric Study of Short Period Variable Stars

This thesis describes an attempt to discover short period variable stars in globular cluster M53 (NGC 5024) with the periods less than 0.2 days. To understand the nature of oscillation of short period variable stars, a detailed study was made on Delta Scuti type variable star SZ Lyn (HD 67390).First part of the study is focused on the identification of short period variables in crowded star field of the globular cluster M53 using BVR photometry. The 1.2 m reflector telescope at Mount Abu observatory in India was used for observations during the first half of 2013. In order to identify the short period variable stars, the temporal variations of light curves were determined in deci-magnitude scale. Point Spread Function (PSF) was used for deconvolving the contaminated faint stars with the bright sources in the dense globular cluster. The light curves of over 3000 stars in the field have been tested for the variability. Light curves of 21 stars with the periods between 0.02 and 0.2 days were detected as short period variable stars.The second part of the study is based on the observations of SZ Lyn, a large amplitude Delta Scuti type binary star, using 50 cm CDK telescope at Mount Abu. The CCD detector has a sensitivity to detect deci-maginitude scale short period variables in very short exposures. To understand the periodic variations of BVR color and the behavior of the oscillations, high time resolution BVR light curves were obtained and analyzed. The study stressed on the oscillations of SZ Lyn beyond the well observed main oscillation period of 0.120 days. The well resolved light curves clearly revealed the main pulsation periods of BVR bands and the presence of their harmonics. The main pulsation periods were determined as 0.120(+/-)0.003 days for B, 0.118(+/-)0.010 days for V and 0.118(+/-)0.002 days for R and there is no significant change of the periods with the color. Apart from the fundamental oscillation, two harmonics were also clearly detected in each band. In addition to the prominent fundamental mode of oscillation, low amplitude non-radial oscillation modes are also present in the light curves. The non-radial oscillations are characterized by oscillations in three orthogonal directions, n - radial mode, l - degree of the mode and m - azimuthal order. The degree of the mode, l for SZ Lyn was determined as l = 1. To the best of our knowledge this is the first time that a study on the oscillation modes of SZ Lyn is made.