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Дата изменения: Fri Mar 5 20:13:59 1999
Дата индексирования: Sat Sep 11 21:07:20 2010
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Поисковые слова: южная атлантическая аномалия

Results and Discussion

In Figures 2 and 3 we show the 6m telescope spectra of blue compact galaxies HS 1013+3809 and HS 1442+4250, in which typical high excitation HII-region narrow emission lines are seen. They are H$\beta$ $\lambda$4861, [OIII] $\lambda\lambda$4959,5007 and $\lambda$4363, several lines of HeI, [NeIII] and [ArIV] for both spectra and H$\alpha$ $\lambda$6562, [NII] $\lambda\lambda$6548,6584 and [SII] $\lambda\lambda$6716,6731 Å for red part of HS 1442+4250. We postpone more detailed analysis of these spectra in conjunction with other observational data to forthcoming paper. In here we use only the observed intensities of important hydrogen and oxygen lines to derive the oxygen abundance in both BCGs. They are presented in Table 1, as well as those corrected for extinction and underlying Balmer absorptions (Izotov et al. 1997a). All intensities of lines are given relative to H$\beta$, along with the equivalent width of H$\beta$ line EW(H$\beta$), the observed H$\beta$ flux F(H$\beta$), the extinction coefficient C(H$\beta$) and observed redshift. To derive T_e in regions of OIII and OII and oxygen abundance, we followed the algorithms also described in Izotov et al. (1997a). To estimate electron density N_e(SII) in HS 1442+4250 the intensity ratio of [SII] lines $\lambda\lambda$6716 and 6731 Å was used as usual. Since the observed ratio the value N_e= 10 cm^-3 was used (Aller 1984) for this object. For HS 1013+3809 the typical for BCGs value N_e= 10 cm^-3 was adopted as well.

The BCG's absolute blue magnitudes presented in Table 1 are calculated with the KUG and UGC catalogs' apparent B-magnitudes and measured heliocentric velocities. The Galaxy extinction correction is not applied since it is very small in comparison with apparent magnitude uncertainties. For so nearby galaxies to get higher precision estimate of their distance the Virgo flow correction and the motion relative to Local group is necessary to take into account (e.g. Kraan-Korteweg, 1986). This correction $\Delta V$ = 354 km s^-1 was calculated for HS 1013+3809 and $\Delta V$ = 202 km s^-1 for HS 1442+4250. The Hubble constant was adopted as 75 km s^-1 Mpc^-1.

Well known Wolf-Rayet features are seen in the spectrum of HS 1442+4250, what makes it interesting for study evolution of massive stars in this galaxy on the time-scale of few Myr (Izotov et al. 1997b).

The morphology of these two galaxies is very different. While HS 1013+3809 looks very symmetric and very compact, with intense star formation burst taking place in its very center, HS 1442+4250 is well elongated, resembling edge-on disk. Strong star formation burst in SW knot is well outside the center of symmetry of this elongated configuration. Another fainter knot from the opposite side of this "disk" is well seen on DSS image, but its spectrum is not yet obtained. This different morphology and relative positions of star formation regions indicate possible different mechanisms of bursting star formation in gas-rich low-mass galaxies.