Optical observations of Dwingeloo 1, a nearby barred spiral galaxy behind the Milky Way

We present new optical observations of the nearby barred spiral galaxy Dwingeloo 1 (Dw1) obtained with the Isaac Newton, William Herschel and Wise telescopes. Dw1 lies at Galactic coordinates (l=138.degrees 52, b=-0.degrees 11) and it is heavily obscured by dust and gas in the Milky Way. We infer that Dw1 is of morphological type SBb or SBc (T=4), has an inclination i approximate to 50 degrees, a position angle PA approximate to 110 degrees, and a recession velocity relative to the Milky Way V-MW=256+/-9 km s(-1). The measured total apparent magnitudes of Dw1 are V=14.0+/-0.5, R=12.2+/-0.2 and I=10.7+/-0.2. The extinction estimate towards Dw1 is highly uncertain. The extinction in the B band, derived from Galactic H I column density measurements, is A(B) approximate to 5.8. Estimated from Galactic 100-mu m emission, the extinction is A(B) approximate to 4.3, while the reddened colours of Dw1 yield an estimate of A(B) approximate to 10.4. Assuming A(B)=-5.8, Tully-Fisher relations in the I and R bands lead to a distance estimate for Dw1 of D approximate to 300 km s(-1). However, for the derived range of extinction estimates 4.3 less than or similar to A(B) less than or similar to 10.4, the distance varies from 100 to 500 km s(-1). We also report the detection of numerous H II regions associated with Dw1, and present data from the Infrared Astronomical Satellite (IRAS) archive.