The distance to the supernova remnant CTB 87 and the radial velocity of the perseus arm toward l=75°, derived from H I and CO observations

We present the results of an analysis of H I data from the Canadian Galactic Plane Survey and new CO observations in the direction of the radio-bright, filled-center supernova remnant (SNR) CTB 87. Our CO (1-0) and CO (3-2) data reveal evidence for associated molecular material surrounding parts of CTB 87 at a systemic velocity of v(LSR) approximate to -58 km s(-1). There is no evidence of interacting H I or the existence of a stellar wind bubble around the SNR. This indicates a supernova explosion of Type II and a B2 or later type progenitor star. We established a new distance of 6.1+/-0.9 kpc based on the extinction-distance relation introduced by Foster & Routledge, which agrees with a location within the Perseus spiral arm. Our result contradicts previous distance estimates based on H I absorption measurements, which indicated a distance of about 12 kpc, using a. at rotation curve. This discrepancy arises from a significant shift of the radial velocities in the direction of CTB 87 due to a spiral shock. The new distance reduces the derived physical size and the luminosity of CTB 87 by factors of 2 and 4, respectively. The properties of this plerionic SNR are then more similar to those of the other SNRs of its kind except the Crab Nebula, which is an exceptionally luminous object.