THE RINGED, WARPED AND ISOLATED GALAXY NGC-6015

We have studied the neutral hydrogen component of the ringed and unbar red Scd galaxy NGC 6015 with the Westerbork telescope at a resolution of 13.6 '' x 15.4 '' (alpha x delta) and a velocity resolution of 33 k m s(-1). These data have been supplemented with CCD-BVRI surface photo metry and optical spectroscopy. The study of the stellar and HI gas co mponent of NGC 6015 shows that its structure changes from small to lar ge radii. In the inner 60 '' there is a blue two armed spiral structur e, previously measured by Elmegreen and Elmegreen. In the following 30 '' the pattern changes to a flocculent one. At 90 '' two pseudoarms s tart, the outer parts winding in a blue pseudoring 153 ''.1 x 56 ''.1 in size. About 41% of the HI emission is concentrated in this ring. Th e extent of the HI gas is about twice that of the optical emission, an d an analysis of the HI distribution and velocity field indicates that NGC 6015 is warped tit radii larger than 170 ''. In the inner parts t he velocity field can be modelled well by normal circular rotation in a disk of the same extent as the optical one. Assuming, as is known to be the case for barred galaxies, that the outer pseudoring is at the outer Lindblad resonance, we derive a value for the pattern speed of 2 6.5 km s(-1) kpc(-1) The expected locations for the other resonances t hen follow from the combined optical/HI rotation curve, and in particu lar we find that the end of the inner spiral structure is located at t he ultraharmonic (4:1) resonance, in agreement with the result found b y Patsis et al. for Sb and Sc type galaxies.