**Table 7:** Main parameters of DDO 68 and I Zw 18
Parameter	DDO 68¹	I Zw 18
Type	Im/BCD	BCD
$B_{\rm tot}$	14.60	16.12²
$(B-V)_{\rm tot}$	0.17	0.11²
$(V-R)_{\rm tot}$	0.17³	0.12²
$V_{\rm Hel}$ (km s^-1)	502	751⁴
D (Mpc)	6.5³	15⁸
E(B-V)⁵	0.018	0.032
M_B⁰	-14.33	-14.89
Angular size ( $^{\prime \prime }$ ) $^{\ddag }$	103 $\times$ 38³	23 $\times$ 13²
Optical size (kpc)	3.2 $\times$ 1.2³	1.5 $\times$ 0.8
12+ $\log$ (O/H)	7.21	7.17^6,7
H $\alpha$ flux^*	1.73³	3.52⁹
H I flux^**	26.7	2.97⁴
W₅₀ (km s^-1)	78	49⁴
W₂₀ (km s^-1)	85	84⁴
M(H I) (10⁸ $M_{\odot}$ )	2.6	1.6
M(H I)/L_B^***	1.85	1.29

$B_{\rm tot}$ - total blue magnitude; M_B⁰ - absolute blue mag. L_B - total blue luminosity. ^* Units of 10^-13 erg s^-1; ^** Units of Jy km s^-1; ^*** in units of (M/L_B) $_{\odot}$ . $^{\ddag }$ $a \times b$ at the surface brightness $\mu_{B}=25$ mag arcsec^-2.
References: ¹ DDO 68 parameters without reference are from Karachentsev et al. (2004); ² Papaderos et al. (2002); ³ this paper; ⁴ van Zee et al. (1998; ⁵ Schlegel et al. (1998); ⁶ Izotov et al. (1999); ⁷ Kniazev et al. (2003); ⁸ Izotov & Thuan (2004); ⁹ Gil de Paz et al. (2003).

Source LaTeX | All tables | In the text

	1 Introduction
	2 Observations and reduction
	3 Results
	4 Discussion and conclusions
	References