UCM 1612 + 1308 : a newly identified Blue Compact Galaxy ?

UCM1612+1308 is a new emission-line galaxy identified in the context of the Universidad Complutense de Madrid (UCM) survey. This object was classified as Blue Compact Galaxy (BCG) from photometric data. A detailed spectroscopic study fromnewoptical observations is presented now.The physical conditions and chemical composition are derived. The ionic abundances yield to a metallicity of 0.23 ± 0.01 Z and a very low nitrogen to oxygen abundances ratio, log (N/O) = −1.74± 0.07, supporting a primary nucleosynthesis origin for the nitrogen. The same value has been obtained for the sulfur to oxygen ratio. The comparison of the helium abundance with the oxygen and nitrogen abundances evidences a quickly enrichment of oxygen produced by massive stars. The ionizing cluster has been analyzed yielding a relatively low ionization parameter, log Ū = −3, total number of stars, logN∗ = 6.18, stellar mass, logM∗ = 5.71M , and gas mass logMg = 7.42M . A lower limit of the dust mass, logMdust = 5.65M , has been obtained from the IRAS fluxes. The observed data and derived parameters, when interpreted with the evolutionary synthesis models by Leitherer & Heckman (1995), point out to an instantaneous burst with an age of log t = 6.7 yr.