We present spectroscopic observations of the nearby dwarf galaxy AGC 198691 .
This object is part of the Survey of H I in Extremely Low-Mass Dwarfs ( SHIELD ) project , which is a multi-wavelength study of galaxies with H I masses in the range of 10 ^ { 6 } -10 ^ { 7.2 } M _ { \odot } discovered by the ALFALFA survey .
We have obtained spectra of the lone H ii region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph ( KOSMOS ) on the Mayall 4-m as well as with the Blue Channel spectrograph on the MMT 6.5-m telescope .
These observations enable the measurement of the temperature-sensitive [ O III ] \lambda 4363 line and hence the determination of a “ direct ” oxygen abundance for AGC 198691 .
We find this system to be an extremely metal-deficient ( XMD ) system with an oxygen abundance of 12+log ( O/H ) = 7.02 \pm 0.03 , making AGC 198691 the lowest-abundance star-forming galaxy known in the local universe .
Two of the five lowest-abundance galaxies known have been discovered by the ALFALFA blind H I survey ; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies .