The Magellanic Irregular Galaxy DDO 50
The Magellanic irregular galaxy, DDO 50 (= Ho II = A 813+70 = VII Zw 223 = Arp 268), is usually assumed to be a member of the M 81 group. De Vaucouleurs (1979) has derived the distance modulus of the galaxy, μ o = 27.79, from magnitudes of the brightest blue supergiants and brightest red variable given by Sandage and Tammann (1974). The estimated absolute magnitude of the galaxy, M T = −17.04, is close to that of the SMC. We have used B and V plates to obtain a colour-magnitude diagram for this galaxy. We have also obtained further estimates of the distance modulus: first, from measurements of the sizes of H II rings in the galaxy from a deep Hα plate, and second, from a comparison of the luminosity function of the brightest blue stars with the corresponding luminosity function for the SMC.
KeywordsLuminosity Function Distance Modulus Versus Plate Distance Indicator Field Star
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