Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.sao.ru/precise/Laboratory/Publications/2000/0822_AA_v0/node11.html
Дата изменения: Sat Mar 11 12:16:53 2000
Дата индексирования: Sat Sep 11 21:00:09 2010
Кодировка:
Поисковые слова: astro-ph

Chemical abundances

The results from the chemical abundance determination are presented in Table 3. For the sake of comparison, we also show the data for the other two low metallicity galaxies SBS 0335-052 and I Zw 18. A two-zone photoionized H II region has been assumed; the electron temperature for the high-ionization region has been obtained from the [O III] $\lambda$4363/($\lambda$4959+5007) ratio using a five-level atom model (Izotov & Thuan [1999]) and for the low-ionization region by using the empirical relation between both electron temperatures (Izotov, Thuan & Lipovetsky [1997b]). The electron density was derived from the [S II]$\lambda$6717,6731 ratio. Abundances have been calculated following Izotov, Thuan & Lipovetsky ([1994], [1997b]).

The oxygen abundance in HS 0822+3542 is slightly higher than in the other two galaxies. This galaxy is, therefore, one more object filling the gap between the metallicity of I Zw 18 and those for the bulk of BCGs. The comparison of the data on element abundances in HS 0822+3542 with the abundance ratios from Izotov & Thuan ([1999]) shows that all data for HS 0822+3542 agree with the derived average values for the sample of low-metallicity BCGs. The largest deviation occurs in the N/O ratio. But if we take into account the large uncertainty in the flux of [N II] $\lambda$6583 emission line blended with H$\alpha$, the N/O is consistent with the expected value for this kind of galaxies.

We thus conclude that the measured ratios of heavy element abundances to that of oxygen in HS 0822+3542 follow the same relation as in all metal-poor BCGs. In particular, nitrogen is likely synthesized in massive stars that also produce oxygen, neon and sulfur, as proposed by Izotov & Thuan ([1999]).

We note, that low measured value of C(H$\beta$)=0.005$\pm$0.04, transfered to a 2$\sigma$ upper limit: C(H$\beta$) < 0.085, equivalent to E(B-V) = 0.68 C(H$\beta$)