L. N. Berdnikov

Rate of Period Change as a Diagnostic of Cepheid Properties

ABSTRACT The rate of period change \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

An Unusual Brightening Of Eta Carinae

\dot{P}

The Period Changes of Polaris

\end{document} 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, the likely location of the object within the instability strip. The 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 disp...

RR Lyrae variables: visual and infrared luminosities, intrinsic colours and kinematics

HST/Space Telescope Imaging Spectrograph data show that the apparent near-UV, visual-wavelength, and near-IR brightness of η Car increased by a factor of two during 1998. Meanwhile its Homunculus ejecta nebula brightened by about 30%, the largest fluctuation of this type in the past 40 years. These developments were quite unexpected and are not easy to explain. Some dust has probably been destroyed, while the stars luminosity may have increased even though it was already close to the Eddington limit. Such a rapid luminosity change would be a truly remarkable phenomenon, not predicted by existing models.

On the crossing mode of the long-period Cepheid SV Vulpeculae

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 stars pulsation period increased at a rate of 4.5 s yr–1 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 –0.055%. 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–1. 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.

Hipparcos red stars in the HpVT2 and

We use UCAC4 proper motions and WISE W1-band apparent magnitudes intensity-mean 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- relation and those of the period-metallicity- -band and period-metallicity- -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 (U0(Halo), V0(Halo), W0(Halo)) = (-7 +/- 9, -214 +/- 10, -10 +/- 6) km/s and (U0(Disc), V0(Disc), W0(Disc)) =(-13 +/- 7, -37 +/- 6, -17 +/- 4) km/s, respectively, and the corresponding components of the velocity-dispersion ellipsoids, (sigma VR(Halo), sigma Vphi(Halo), sigma Vtheta(Halo)) = (153 +/- 9, 101 +/- 6, 96 +/- 5) km/s and (sigma VR(Disc), sigma Vphi(Disc), sigma Vtheta(Disc)) = (46 +/- 7, 37 +/- 5, 27 +/- 4) km/s, respectively. The fraction of thick-disc stars is estimated at 0.22 +/- 0.03. The corrected IR period-metallicity-luminosity relations are = -0.769 +0.088 [Fe/H]- 2.33 mathoprm log PF and = -0.825 + 0.088 [Fe/H] -2.33 mathoprm log PF, and the optical metallicity-luminosity relation, [Fe/H]- , is = +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.

V\!I_{\rm C}

The Cepheid SV Vul is demonstrated to be in the second crossing of the instability strip on the basis of its well- defined period decrease of −214.3 ± 5. 5s yr −1 . Recent arguments from its atmospheric abundance pattern that it is in the first crossing are not supported by the historical photometric data. Furthermore, an examination of atmospheric abundance patterns for other Cepheids in advanced strip crossing modes suggests that the presence of CNO-processed material in the atmospheres of intermediate-mass stars does not arise from red supergiant dredge-up phases but from meridional mixing during previous evolution as rapidly-rotating main-sequence B-type stars.

systems

For Hipparcos M, S, and C spectral type stars, we provide calibrated instantaneous (epoch) Cousins

Photoelectric observations of southern Cepheids in 2001

V-I

BINARY PROPERTIES FROM CEPHEID RADIAL VELOCITIES (CRaV)

color indices using newly derived