Fig. 1

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RGB image of Holmberg II with HE red, YE green, and IE blue. Foreground extinction has been corrected and sky subtracted as described in the text (Sect. 4.1). In the top panel, the full FoV of 0.7 × 0.7 is shown, while the bottom panel displays the inner 6’ × 6 ’ region corresponding to the white box in the upper panel. In the lower panel, to the east, there is an extensive north-south chain of H II regions (e.g., Hodge et al. 1994) that harbors the ultraluminous X-ray source Ho II ULX-1 (e.g., Zezas et al. 1999; Kaaret et al. 2004), visible as a triangular-shaped blue H II region at α = 08:19:28.98, δ = +70:42:19.3 (J2000). Also visible as a blue circular structure to the north of the H II-region chain is an artifact dichroic ghost (see also Sect. 6, Fig. 15).
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