We present elemental abundances for multiple HII regions in Leo A and GR 8 obtained from long slit optical spectroscopy of these two nearby low luminosity dwarf irregular galaxies .
As expected from their luminosities , and in agreement with previous observations , the derived oxygen abundances are extremely low in both galaxies .
High signal-to-noise ratio observations of a planetary nebula in Leo A yield 12 + log ( O/H ) = 7.30 \pm 0.05 ; “ semi-empirical ” calculations of the oxygen abundance in four HII regions in Leo A indicate 12 + log ( O/H ) = 7.38 \pm 0.10 .
These results confirm that Leo A has one of the lowest ISM metal abundances of known nearby galaxies .
Based on results from two HII regions with high signal-to-noise measurements of the weak [ O III ] \lambda 4363 line , the mean oxygen abundance of GR 8 is 12 + log ( O/H ) = 7.65 \pm 0.06 ; using “ empirical ” and “ semi-empirical ” methods , similar abundances are derived for 6 other GR 8 HII regions .
Similar to previous results in other low metallicity galaxies , the mean log ( N/O ) = - 1.53 \pm 0.09 for Leo A and - 1.51 \pm 0.07 for GR 8 .
There is no evidence of significant variations in either O/H or N/O in the HII regions .
The metallicity-luminosity relation for nearby ( D < 5 Mpc ) dwarf irregular galaxies with measured oxygen abundances has a mean correlation of 12 + log ( O/H ) = 5.67 - 0.151 M _ { B } with a dispersion in oxygen about the relationship of \sigma = 0.21 .
These observations confirm that gas-rich low luminosity galaxies have extremely low elemental abundances in the ionized gas-phase of their interstellar media .
Although Leo A has one of the lowest metal abundances of known nearby galaxies , detection of tracers of an older stellar population ( RR Lyrae variable stars , horizontal branch stars , a well populated red giant branch ) indicate that it is not a newly formed galaxy as has been proposed for some other similarly low metallicity star forming galaxies .