Star formation in blue compact dwarf galaxies: Mkn 104 and I Zw 97

Two blue compact dwarf galaxies Mkn 104 and I Zw 97 are studied photometrically and spectroscopically. Mkn 104 is found to contain three distinct bright star forming regions, whereas I Zw 97 is found to contain three bright and two faint star forming regions. Medium resolution spectra of three bright H ii regions in the two galaxies were obtained. Estimation of oxygen abundance in these regions yields a value equal to log(O/H)+12 = 8.5 (Z = Z⊙/2.7). Star formation rates in these star forming regions are estimated. The highest star formation rate for I Zw 97 is found to be 0.04 M⊙yr −1 and for Mkn 104, it is 0.02 M⊙yr −1 . I Zw 97 is realized to be a cometary blue compact dwarf galaxy undergoing a strong burst of star formation. A U B vs V I colour-colour mixed population model is created using the Starburst99 evolutionary model curves. The spectrum of the bright star forming knot of I Zw 97 does not show any strong signature of an underlying relatively older stellar population, but the U B vs V I two colour diagram indicates a strong contribution of a � 500 Myr population. A spectrum of the central region of Mkn 104 gives a hint about the underlying old stellar population. The age of this underlying population using the U B vs V I two colour diagram is estimated to be � 500 Myr. Surface brightness profiles and colour profiles for these galaxies are presented. The surface brightness profile of both