1 Introduction

Extremely metal-deficient gas-rich galaxies (commonly taken as objects with an ionized gas metallicity $Z \lesssim 1/20~Z_{\odot}$) have received much attention recently. The discovery of an unusually low metallicity of the ionized gas in the blue compact galaxy (BCG) I Zw 18 (Mkn 116) (Searle & Sargent 1972) led to the claim that such objects can be considered as the best candidates for truly local young galaxies. However, the search for similar galaxies conducted by several groups (e.g., Sargent & Kunth 1986; Terlevich et al. 1991) has failed to find a large population with such extremely low metallicities. In their review, Kunth & Östlin (2000) summarize and discuss many problems related to very metal-poor galaxies and they present a compilation of all the known gas-rich galaxies with $Z \lesssim 1/20~Z_{\odot}$. From the analysis of the ratios of C/O and N/O abundances Izotov & Thuan (1999) suggested that the lowest metallicity blue compact galaxies should experience their first episode of star formation (SF) and therefore the hypothesis of youth for these galaxies needs to be carefully studied. In any case the properties of such galaxies best approximate those of young low-mass galaxies formed at the epoch of galaxy formation.

Therefore, very metal-poor galaxies in the Local Universe attract much attention, and multiwavelength studies of such objects have been performed to better identify their nature. However not all such galaxies found in the early studies as very metal-deficient (Kunth & Östlin  2000) have spectroscopic data of sufficient quality for an accurate determination of the metallicity. Since detailed studies of individual galaxies require significant effort and observational time, thus, one should be confident about the very low metallicity of the selected galaxies.

In Paper I (Kniazev et al. 2001a) we reported a revision of 3 BCGs from the list of Kunth & Östlin (2000). For one, the low metallicity value was confirmed while the other two showed an underestimation of 0.4 dex. In this paper we present high S/N spectroscopy of two more BCGs (UM 408 and A 1228+12) from the list by Kunth & Östlin (2000), for which the metallicity determination raised some concerns, and one galaxy (UM 151) from the work by Telles (1996). All these galaxies were claimed as $Z \sim 1/20~Z_{\odot}$ objects based on the results of earlier spectroscopy. As a result of the previous and present work the number of extremely metal-deficient BCGs from the Kunth & Östlin list has decreased by $\sim$20%. The remaining objects are in fact representative of very metal-deficient BCGs and deserve detailed multiwavelength studies.