2 Observations and data reduction

The observations of SBS 0335-052 were carried out on January 9, 2000 on the Keck II telescope with the low-resolution imaging spectrograph (LRIS) (Oke et al. 1995), using the 300 groove mm^-1 grating which provides a dispersion 2.52 Å pixel^-1 and a spectral resolution of about 8 Å in first order. The slit was 1 $^{\prime\prime}$$\times$180 $^{\prime\prime}$, centered on the brightest H II region and oriented along the major axis with a position angle PA = -30$^\circ$. No binning along the spatial axis has been done, yielding a spatial sampling of 0 $.\!\!^{\prime\prime}$2 pixel^-1. The total exposure time was 60 min, broken into four 15 min exposures. All exposures were taken at an airmass of 1.1. The seeing was 0 $.\!\!^{\prime\prime}$9. Wavelength calibration was provided by Hg-Ne-Ar comparison lamp spectra obtained after each exposure. Two spectrophotometric standard stars, Feige 34 and HZ 44, were observed for flux calibration. The data reduction was made with the IRAF software package. The two-dimensional spectra were bias-subtracted and flat-field corrected. Cosmic-ray removal, wavelength calibration, night sky background subtraction, correction for atmospheric extinction and absolute flux calibration were then performed.

For the analysis of spatial distribution of the brightest emission lines we also use the Keck spectrum of SBS 0335-052 obtained earlier by Izotov et al. (1999) at a position angle of 80$^\circ$.

A distance of 54 Mpc to SBS 0335-052 is adopted throughout this paper (Izotov et al. 1997). At this distance, 1 $^{\prime\prime}$ corresponds to 260 pc.

The spectrum of the brightest region in a 1 $^{\prime\prime}$$\times$2 $.\!\!^{\prime\prime}$2 aperture with secure and tentative line identifications (see below) is shown in Fig. 1. The measured S/N is of the order of 100. Extinction-corrected fluxes of the emission lines normalized to the flux of 10 $^{-4}\times I$(H$\beta$) are shown in Table 1.

   

Table 1: Extinction-corrected fluxes of the emission lines in the brightest region.

$\lambda_{0}$(Å) Ion	$\lambda_{\rm obs}^{\rm a}$	I($\lambda$)$^{\rm b}$			$\lambda_{0}$(Å) Ion	$\lambda_{\rm obs}^{\rm a}$	I($\lambda$)$^{\rm b}$			$\lambda_{0}$(Å) Ion	$\lambda_{\rm obs}^{\rm a}$	I($\lambda$)$^{\rm b}$
3727 [O II]	3728	2136			4815 [Fe II]	4814	9			5876 He I	5875	1043
3750 H12	3751	393			4861 H$\beta$	4861	10000			?	5917	4
3771 H11	3771	471			4907 [Fe IV]?	4904	22			?	5932	3
3798 H10	3798	597			4922 He I	4922	94			5958 Si II	5957	8
3820 He I	3820	75			4959 [O III]	4959	10663			5979 Si II	5978	8
3835 H9	3836	798			5007 [O III]	5007	32271			?	5999	3
3868 [Ne III]	3869	2349			5085 [Fe III]	5080	6			6046 O I	6044	5
3889 H8 + He I	3890	1741			?	5097	3			6074 He II	6075	3
3926 He I	3927	27			5112 [Fe II]	5112	6			?	6085	2
?	3943	31			5146 [Fe VI]	5149	15			6102 He II	6100	4
3968 [Ne III] + H7	3969	2478			5159 [Fe II], [Fe VII]	5160	15			?	6150	4
4009 He I	4009	11			5176 [Fe VI]	5181	7			6170 He II	6169	2
4026 He I	4027	137			5199 [N I]	5198	33			?	6270	3
4068-76 [S II]	4071	44			?	5214	3			6300 [O I]	6300	87
4101 H$\delta$	4102	2604			?	5235	5			6312 [S III]	6311	51
4121 He I	4122	16			?	5244	2			6347 Si II	6346	8
4144 He I	4145	20			5262 [Fe II]	5259	7			6363 [O I]	6363	32
4169 He I	4168	11			5271 [Fe III]	5270	242			6407 He II	6407	4
4227 [Fe V]	4228	36			?	5309	6			?	6455	9
4287 [Fe II]	4288	18			5335 [Fe VI]	5336	6			6563 H$\alpha$	6562	27366
?	4314	12			?	5351	2			6678 He I	6677	260
4340 H$\gamma$	4341	4753			?	5369	4			6717 [S II]	6716	197
4363 [O III]	4364	1089			?	5390	2			6731 [S II]	6731	166
4388 He I	4389	43			5411 He II	5412	13			7002 O I	7002	13
4415 [Fe II]	4416	12			5424 [Fe VI]	5424	2			?	7038	5
?	4434	10			?	5436	2			7065 He I	7065	427
4452 [Fe II]	4453	6			5485 [Fe VI]	5482	2			7136 [Ar III]	7135	212
4471 He I	4472	344			?	5501	5			7171 [Ar IV]	7170	7
4511 N III	4509	7			5517 [Cl III]	5517	13			?	7195	2
4565 Si III	4566	10			5538 [Cl III]	5537	10			?	7210	2
?	4581	8			?	5552	5			?	7224	2
4603-20 N V?, N III?	4609	32			?	5580	3			7237 [Ar IV]	7237	3
4640 N III	4641	13			?	5595	4			7254 O I	7254	10
4658 [Fe III]	4659	43			?	5608	3			7263 [Ar IV]	7264	5
4686 He II	4686	221			5639 [Fe VI]	5638	3			7281 He I	7280	52
4711 [Ar IV]+He I	4712	182			5677 [Fe VI]	5678	7			7298 He I	7295	5
4740 [Ar IV]	4741	104			?	5698	2			7320 [O II]	7319	60
4755 [Fe III]	4757	7			5721 [Fe VII]	5721	10			7330 [O II]	7330	28

$^{\rm a}\lambda_{\rm obs}$ = $\lambda_{\rm measured}$/(1+z), where $\lambda_{\rm measured}$ is the measured wavelength
of the emission line, z = 0.0135 is the redshift of SBS 0335-052.
$^{\rm b}$ I($\lambda$) is normalized to the flux of 10 $^{-4}\times I$(H$\beta$).