Orientation parameters of the Cepheid system in the Galaxy

Based on the distribution of long-period Cepheids, we have redetermined the orientation parameters of their principal plane in the Galaxy. Based on 299 Cepheids with heliocentric distances r < 20 kpc and pulsation periods P a parts per thousand yen 5(d), we have found the directions of the three principal axes of the position ellipsoid: L (1) = 281.0A degrees +/- 0.1A degrees, B (1) = -1.9A degrees +/- 0.1A degrees; L (2) = 11.0A degrees +/- 0.7A degrees, B (2) = 0.2A degrees +/- 0.1A degrees; and L (3) = 275.9A degrees +/- 0.7A degrees, B (3) = 88.1A degrees +/- 0.1A degrees. Thus, the line of nodes l (Omega) = L (3) + 90A degrees = 5.9A degrees is very close to the direction to the Galactic center; the Cepheid symmetry plane is inclined to the Galactic plane approximately by -2A degrees in the direction of the first axis (L (1)). The direction of the line of nodes found from old Cepheids (P < 5(d)) differs significantly and is l (Omega) = 298A degrees. The elevation of the Sun above the Galactic plane has been estimated from 365 closer stars (r < 4 kpc) without any constraint on the pulsation period to be h (aS (TM)) = 23 +/- 5 kpc.