Optical and UV studies of type Ia supernovae SN 2009ig and SN 2012cg

We present an extensive optical–ultraviolet photometry and analysis of a series of optical spectra of type Ia supernovae SN 2009ig and SN 2012cg. The observations range from −15 to +185 d for SN 2009ig and from −14 to 316 d for SN 2012cg, with respect to maximum light in B band. Both SN 2009ig and SN 2012cg exhibit similar properties. They have similar decline rate parameter (Δm15(B)true = 0.92 ± 0.04 for SN 2009ig and 0.93 ± 0.06 for SN 2012cg) and B band peak absolute magnitude (−19.45 ± 0.40 mag for SN 2009ig and −19.50 ± 0.31 mag for SN 2012cg). Their early spectra show high-velocity features in Si ii and Ca ii lines. The strong Fe iii, Si iii, and weak Si ii λ5972 line during pre-maximum phase are indicative of hot photosphere. The post-maximum velocity evolution shows a plateau like phase with velocities ∼13 000 km s−1 for SN 2009ig and ∼10 000 km s−1 for SN 2012cg. Both events show spectral evolution similar to normal SNe Ia and fall in LVG and Core Normal subgroup. Both have smaller strength ratio [$\cal R$(Si ii) = 0.17 for SN 2009ig and 0.20 for SN 2012cg] consistent with smaller Δm15(B). Peak bolometric luminosities ($\log L_\text{bol}^\text{max}$) of these events are estimated as 43.17 ± 0.16 and 43.24 ± 0.11 erg s−1 suggesting that 0.60 ± 0.20 M⊙ of 56Ni was synthesized in the explosion of SN 2009ig and 0.72 ± 0.31 M⊙ in SN 2012cg.