We serendipitously find a new nearby Low Surface Brightness ( LSB ) galaxy from SDSS database .
We estimate oxygen abundance of its H ii region SDSS J121811.0+465501.2 from electron temperature , as well as for another H ii region , SDSS J135440.5+535309.6 , located in irregular LSB galaxy UGC 8837 .
These two extragalactic H ii regions were classified as stars in the SDSS-DR4 database , and were found occasionally by us in the automatic recognition and classification on stellar spectra .
Their optical spectra show obvious emission lines , i.e. , strong [ O iii ] \lambda \lambda 4959 , 5007 , Balmer emission lines , but very weak [ N ii ] \lambda \lambda 6548,6583 and [ S ii ] \lambda \lambda 6317,6731 , which could indicate that they are metal-poor star-forming regions .
The derived oxygen abundances of the two objects are 12+log ( O/H ) \sim 7.88 \pm 0.30 and 7.70 \pm 0.30 , respectively .
The host of the H ii region SDSS J121811.0+465501.2 is identified as a new nearly edge-on LSB disc galaxy ( almost without bulge ) with the B -band central surface brightness \mu _ { 0 } ( B ) as 23.68 mag arcsec ^ { -2 } and inclination angle as \sim 75 degree by using the GIM2D software to analyze its g - and r - band images independently .
It is a nearby dwarf galaxy with redshift z \sim 0.00157 , disk scale-length \sim 0.40 kpc and B -band absolute magnitude M _ { B } \sim - 13.51 mag .
The very low oxygen abundances of these two objects confirm the low metallicities of LSB galaxies .