A kinematic check of the distance scale of Galactic Cepheids

Sammanfattning: A selection of well known period luminosity relations for cepheid variables are studied under the assumption that cepheid variables have a mean vertical velocity of zero in the galactic plane. Proper motion data from Hipparcos and Thyco-2 catalogues are coupled with the distances obtained from applying the period luminosity relations on a database of known classical cepheids to calculate the velocities of the cepheids. A statistical analysis is performed on the velocities to identify the best sample of cepheids to perform the kinematic check on. Two samples are found depending on whether the period luminosity relation has a colour term or not. Examining the samples leads to rejecting one sample and the other sample shows that in order to agree with the above assumption the solar vertical velocity is unlikely to be around the conventional 7 km/s, but has to be lowered to around 6.5 km/s or less; or the period luminosity relations have to be corrected on the order of -0.2 mag, i.e.\ a little brighter than previously assumed. It is further argued that the correction to the period luminosity relations is more in agreement with other studies than lowering the solar velocity.