SIMBAD references

We present 6.5 m MMT spectrophotometry of 20 H II regions in 13 extremely metal-poor emission-line galaxies selected from Data Release 5 of the Sloan Digital Sky Survey to have [O III] λ4959/Hβ≲1 and [N II] λ6583/Hβ≲0.05. The electron-temperature-sensitive emission line [O III] λ4363 is detected in 13 H II regions, allowing a direct abundance determination. The oxygen abundance in the remaining H II regions is derived using a semiempirical method. The oxygen abundance of the galaxies in our sample ranges from 12+log(O/H)∼7.1 to ∼7.8, with 10 H II regions having an oxygen abundance lower than 7.5. The lowest oxygen abundances, 7.14±0.03 and 7.13±0.07, are found in two H II regions of the blue compact dwarf galaxy SDSS J0956+2849 (≡DDO 68), making it the second most metal-deficient emission-line galaxy known, after SBS 0335-052W.