Rate of period change $\dot{P}$ for a Cepheid is shown to be a parameter that is capable of indicating the instability strip crossing mode for individual objects, and, in conjunction with light amplitude, likely location within the instability strip. Observed rates of period change in over 200 Milky Way Cepheids are demonstrated to be in general agreement with predictions from stellar evolutionary models, although the sample also displays features that are inconsistent with some published models and indicative of the importance of additional factors not fully incorporated in models to date.Comment: Published in PASP (March 2006); TeX source & figures now provide

We use UCAC4 proper motions and WISE W 1-band apparent magnitudes intensitymean for almost 400 field RR Lyrae variables to determine the parameters of the velocity distribution of Galactic RR Lyrae population and constrain the zero points of the metallicity-< M V > relation and those of the period-metallicity-< M Ks >-band and period-metallicity-< M W 1 >-band luminosity relations via statistical parallax. We find the mean velocities of the halo-and thick-disc RR Lyrae populations in the solar neighbourhood to be (U 0 (Halo), V 0 (Halo), W 0 (Halo)) = (−7 ± 9, −214 ± 10, −10 ± 6) km s −1 and (U 0 (Disc), V 0 (Disc), W 0 (Disc)) = (−13 ± 7, −37 ± 6, −17 ±4) km s −1 , respectively, and the corresponding components of the velocity-dispersion ellipsoids, (σV R (Halo), σV φ (Halo), σV θ (Halo)) = (153 ± 9, 101 ± 6, 96 ± 5) km s −1 and (σV R (Disc), σV φ (Disc), σV θ (Disc)) = (46 ± 7, 37 ± 5, 27 ± 4) km s −1 , respectively. The fraction of thick-disc stars is estimated at 0.22 ± 0.03. The corrected IR periodmetallicity-luminosity relations are < M Ks > = -0.769 +0.088 · [Fe/H]-2.33 · log P F and < M W 1 > = -0.825 + 0.088· [Fe/H] -2.33 · log P F , and the optical metallicityluminosity relation, [Fe/H]-< M V >, is < M V > = +1.094 + 0.232· [Fe/H], with a standard error of ± 0.089, implying an LMC distance modulus of 18.32 ± 0.09, a solar Galactocentric distance of 7.73 ± 0.36 kpc, and the M31 and M33 distance moduli of DM M31 = 24.24 ± 0.09 (D = 705 ± 30 kpc) and DM M33 = 24.36 ± 0.09 (D = 745 ± 31 kpc), respectively. Extragalactic distances calibrated with our RR Lyrae star luminosity scale imply a Hubble constant of ∼80 km/s/Mpc. Our results suggest marginal prograde rotation for the population of halo RR Lyraes in the Milky Way. c 2013 RAS

Abstract. We report a new version of the catalogue of distances and light-curve parameters for Galactic classical Cepheids. The catalogue lists amplitudes, magnitudes at maximum light, and intensity means for 455 stars in BV RI filters of the Johnson system and (RI) C filters of the Cron-Cousins system. The distances are based on our new multicolour set of PL relations and on our Cepheidbased solution for interstellar extinction law parameters and are referred to an LMC distance modulus of 18.25.

ABSTRACT. The evolutionary changes in pulsation period for the Cepheid Polaris are reinvestigated using archival observational material (radial velocities, photometry, and eye observations) over the interval 1844 to the present, including new photometry for the star obtained in [2003][2004]. The star's pulsation period increased at a rate of 4.5 s yr Ϫ1 during that interval, with the exception of a brief hiatus between 1963 and 1966, when it suddenly decreased, possibly as a result of a brief reduction in average stellar radius amounting to Ϫ0.055%. At roughly the same time, the pulsation amplitude of Polaris underwent a marked change. Prior to 1963 the V amplitude was in excess of about 0.1 mag, possibly decreasing at a rate of 0.019 mag century Ϫ1 . Following the hiatus of 1963-1966, the pulsation amplitude underwent a sharp decline and now appears to be erratic on a cycle-to-cycle basis, always smaller than 0.05 mag. The rapid rate of period increase for Polaris is consistent with a first crossing of the Cepheid instability strip, while the hiatus of 1963-1966 and sudden decrease in pulsation amplitude thereafter suggest that the star may have left the instability strip for first crossers at that time, leaving it near the center of the instability strip for Cepheids in higher crossing modes.