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Дата изменения: Wed Jan 13 00:37:36 1999
Дата индексирования: Sat Sep 11 22:10:02 2010
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Поисковые слова: ngc 4736

First results from follow-up spectroscopy with the NOT

We report new recent results from the follow-up program carried out with NOT on May 27 to 30, 1998. Preliminary estimates of element abundances in the observed BCGs were obtained on results of lower S/N spectroscopy with 6m telescope, and they indicated extremely low metallicity for one galaxy, and probable very low metallicity for several others (Pustilnik et al. 1998). One of them was the host galaxy for the recent SN 1998bv outburst (Kniazev et al. 1998), and therefore was very interesting for metallicity determination. We obtained medium resolution spectroscopy with ALFOSC by using grisms number 6 and 7 in order to cover the full spectral range from 3700 to 7000 Å. Among the nine observed galaxies we present here the data obtained for 3 of them:

HS 0822+3542 is a very compact star-like system which appears to be an extremely low metallicity galaxy with oxygen abundance 1/30 of the solar value.

HS 1604+4127 seems to be a double system with two knots of star formation. The calculated metallicities for both knots are consistent with homogeneous chemical composition through the system and amount to 1/10 of solar.

HS 1035+4758 is the more extended system of the Irregular type and we present in the next section also the analysis of the Supernova detected in the galaxy. The metallicity has been estimated using empirical methods and all agree with an average of 1/4 of solar.

The most relevant physical parameters for the galaxies are presented in Table 1. It is worthwhile to notice that they are good representative of the kind low luminosity and low metallicity galaxies which normally are being detected in objective prism surveys (see Masegosa et al. 1994, Izotov & Thuan 1998).

 

 

Table: Physical parameters for the targets.

	HS0822+3542	HS1604+4127A	HS1604+4127B	HS1035+4758
te	1.80	1.34	1.26	0.96
O+	0.2e-5	0.2e-4	0.35e-4	0.52e-4
O++	0.26e-4	0.77e-4	0.75e-4	0.13e-4
12 + Log(O/H)	7.45	7.99	8.04	8.26
Ne++	0.34e-5	0.11e-4	0.17e-4	-
12 + Log(Ne/H)	6.56	7.14	7.39	-
W$_{\beta}$	269	195	220	24
Log F $_{H_{\beta}}$	-14.02	-14.23	-14.66	-14.72
z	0.002	0.007	0.007	0.005
MB	-11.50	-13.83	-13.83	-15.83*

^* Distance modulus has been corrected by using a Virgo flow model.

The quality of the data can be judged from Figure 1, where we presented the blue spectra for the observed galaxies.