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KP Cyg: An Unusual Metal-Rich RR Lyr Type Star of Long Period
We present the results of a detailedspectroscopic study of the long-period (P=0.856 days) RR Lyrae star, KPCyg. We derived abundances of many chemical elements including the lightspecies, iron-group elements and elements of the s-processes. Most RRLyrae stars with periods longer than 0.7 days are metal-deficientobjects. Surprisingly, our results show that KP Cyg is very metal rich([Fe/H]=+0.18±0.23). By comparison with a number of short-period(P=1˜6 days), metal-rich CWB stars, we suggest that KP Cyg may bea very short-period CWB star (BL Her star) rather than an RR Lyrae star.As seen in some CWB stars, KP Cyg shows strong excesses of carbon andnitrogen in its atmosphere. This indicates that the surface of KP Cyghas been polluted by material that has undergone helium burning (toenhance carbon) and proton capture (to transform carbon into nitrogen).We also note that UY CrB, whose period is 0.929 days, also shows anenhancement of C and N, and that two carbon Cepheids of short period,V553 Cen and RT TrA, show similar excesses of carbon and nitrogen.
| The Chemical Compositions of the Type II Cepheids-The BL Herculis and W Virginis Variables
Abundance analyses from high-resolution optical spectra are presentedfor 19 type II Cepheids in the Galactic field. The sample includes bothshort-period (BL Her) and long-period (W Vir) stars. This is the firstextensive abundance analysis of these variables. The C, N, and Oabundances with similar spreads for the BL Her and W Vir show evidencefor an atmosphere contaminated with 3α process and CN-cyclingproducts. A notable anomaly of the BL Her stars is an overabundance ofNa by a factor of about 5 relative to their presumed initial abundances.This overabundance is not seen in the W Vir stars. The abundanceanomalies running from mild to extreme in W Vir stars but not seen inthe BL Her stars are attributed to dust-gas separation that provides anatmosphere deficient in elements of high condensation temperature,notably, Al, Ca, Sc, Ti, and s-process elements. Such anomalies havepreviously been seen among RV Tau stars which represent a long-periodextension of the variability enjoyed by the type II Cepheids. Commentsare offered on how the contrasting abundance anomalies of BL Her and WVir stars may be explained in terms of the stars' evolution from theblue horizontal branch.
| Photometry of Type II Cepheids. III. The Intermediate-Period Stars
We present 741 new photometric observations for 22 Cepheids with periodsbetween 3 and 8 days. Many of the stars are probable type II Cepheids,but we have included some type I Cepheids for comparison. The shapes andstability of the shapes of the light curves, the stability of theperiods, and the scatter of individual data points are discussed.Although none of these proves to be a reliable discriminator betweentype I and type II Cepheids, they do permit the identification ofseveral unusual stars.
| The Spectra of Type II Cepheids. II. The Hα Line in Intermediate-Period Stars
We present 98 Hα profiles for 21 pulsating variable stars withperiods from 3 to 8 days. The strength, depth, and shape of Hαvary throughout the cycles of the stars in a way consistent with thetemperature changes. Otherwise, they are quite uniform among all thestars, with a single exception. In FM Del, Hα is weaker and has asmaller central depth than in the other stars. This and the wavelengthshifts of the core are attributed to incipient emission. Thedifferential velocity of Hα relative to the metal lines is lessthan 25 km s-1 for all the stars except QY Cyg, FM Del, andEF Tau. We suggest that this indicates that only these stars are type IICepheids despite the large distances of some of the others from theGalactic plane.Based in part on observations obtained with the Apache Point Observatory3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Fourier Analysis of Hipparcos Photometry of Cepheid Variables
Fourier parameters have been computed for 240 field Cepheids observed bythe Hipparcos satellite. We have identified three new PopulationIovertone Cepheids: V411Lac, V898 Cen and V572 Aql. We have comparedFourier progressions of Population I and Population II Cepheids. Thepossibility of using Fourier parameters to distinguish between the twotypes is discussed.
| UVBY beta Photometric Data and Fourier Coefficients for Galactic Population I and Population II Cepheids
Photometric data in the uvby beta system are presented for a sample of98 Population I Cepheids and seven W Virginis or Population II Cepheids.The importance of the Fourier decomposition technique in the study ofthe structure of pulsating stars is stressed. Mean values and Fourierdecomposition coefficients for the V, b - y, m1, and c1 variations arecalculated. Also, mean values of H beta are provided. New times ofmaximum V light are reported for the majority of the stars in thesample. Significant shifts of the light and color curves were found insome Cepheids; these are explained by their period variations. Thesestars are highlighted in the text.
| Spectroscopic survey of field Type II Cepheids
A sample of relatively bright, short- and intermediate-period (P=1-10d)Type II Cepheids in the Galactic field have been observedspectroscopically with an intermediate-resolution(lambda/Deltalambda=11000) spectrograph. The wavelength region was6500-6700A, including the Hα line and some photospheric ironlines. The signal-to-noise ratio (S/N) was usually between 50 and 100,depending on weather conditions and the brightness of target stars.Radial velocities were determined by cross-correlating the Cepheidspectra with those of selected IAU velocity standard stars having F-Gspectral types. The internal error of the velocity determination processwas calculated to be about 1 km s^-1. Hα emission and strong linesplitting were observed in BL Her during the expansion phase, but nosimilar phenomenon was detected in any other stars in this programme,except for AU Peg which has an unusual Hα line showing a PCygni-like profile. The velocity curve agrees well with recent CORAVELmeasurements. The velocity gradients in Cepheid atmospheres are studiedusing the Hα minus metallic velocities. Similar data are collectedfrom the literature. It seems that having large velocity differences(v_Hα-v_metal>40 km s^-1) is a characteristic feature of thevery short-period (P<1.5d) and longer period (P>10d) Cepheids.Between these period regions the Cepheid atmospheres exhibit smallervelocity differences. Most of the Type II Cepheids observed in thepresent study fall into this latter category. There might be a tendencyfor classical Cepheids of intermediate period to have larger maximumvelocity differences.
| Baade-Wesselink Radius Determination of Type II Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113.1833B&db_key=AST
| The Behlen Observatory variable star survey. Paper 3.
Finding charts, accurate coordinates and light curves are presented for146 variable stars including three which are newly discovered.Parameters descriptive of the light curves are tabulated includingperiods for eight stars which lacked them in the General Catalogue ofVariable Stars (the GCVS). GCVS periods of twelve stars were found to beseriously in error. The classification of the stars is discussed.Revisions or refinements of the classifications from the GeneralCatalogue of Variable of Stars are suggested for thirty-one stars. Ofthe nineteen stars classified as Bailey type c RR Lyrae stars in theGeneral Catalogue of Variable Stars, five are found to be short periodeclipsing or ellipsoidal variables. Seventeen percent of the Bailey typeab RR Lyrae stars and 14% of the type c's show scatter in their lightcurves which is suggestive of the Blazhko effect.
| Stromgren photometry of short period population II Cepheids
Observations of the v, b, and y bands of the Stromgren system arepresented for 13 Cepheids of the disk and halo populations. Data forfour additional stars in the literature are included. Values of (M/H)are derived for each star using theoretical v, b, y colors. The (M/H)values agree quite well with high dispersion investigations of threestars. A range of (M/H) values from -2.3 to +0.5 and greater is found.At least nine of the 17 Cepheids are found to have (M/H) values that aregreater than found in any globular cluster that contains Cepheids. Thehighest M/H values may be due to uncertainties in circumstellarreddening of AU Peg and in the case of HR Aur, the likely presence ofcarbon bands in the spectrum. For the other stars whose (M/H) value isnear zero it is possible that their atmospheres have been polluted byhydrogen-depleted material due to mass loss or mass transfer in a binarysystem.
| A catalogue of field Type II Cepheids
A catalogue of field Type II Cepheids is presented. The primary listconsists of 152 Cepheids sufficiently far from the galactic plane to bevery probably Type II stars. A second list contains 56 additional starsthat are likely, but less certain, Type II Cepheids, including bothstars estimated to be at large distances from the galactic plane butwith uncertain distances and stars close to the galactic plane believedto be Type II for independent reasons.
| Kinematics of field Type II Cepheid variables
The spectra of 49 field Type II Cepheids have been assembled andcombined with 14 additional stars with previously published radialvelocities in order to investigate the kinematics and spectralcharacteristics of these stars. Many of the stars have low peculiarvelocities consistent with circular rotation around the galaxy, whilesome are high-velocity stars. Outside the nuclear bulge, the velocitiesare correlated with photometric metallicities in the sense thatmetal-rich stars show a nearly normal, disklike rotation velocity and alow velocity dispersion. This correlation shows that the low-velocity,metal-rich stars have an old-disk origin. Fewer Cepheids are found inthe field than expected relative to clusters, suggesting a differencebetween the populations of the halo field and clusters. The kinematicproperties of Cepheids in the nuclear bulge appear to be different inthat both metal-poor and metal-rich Cepheids have a high velocitydispersion and show little systematic galactic rotation.
| Period changes of Cepheid variables. I - Secular period changes
Secular period changes of one hundred northern Cepheids are investigatedwith the help of O-C diagrams. With the classical Cepheids the rate ofobserved period changes is in good agreement with that determined fromstellar evolution theory. The period noise cannot mask the evolutionaryperiod changes especially in longer period Cepheids for which theoccurrence of parabolic O-C graphs is unusually frequent.
| Photoelectric UBV Photometry of Northern Cepheids I
New UBV photoelectric observational data on 38 northern cepheids withperiods of less than 5 days are presented. The period changes of theobserved cepheids are investigated. Four variables (SU Cyg, DT Cyg, V532Cyg, SZ Tau) show a period jump and a subsequent 'rejump' to the earliervalue of the period, which results in the overall constancy of theperiod. DT Cyg pulsates with the same period for at least the fourthtime which is in keeping with the recent hypothesis on the evolution ofcepheids along the lines of constant period in the HRD. AU peg, aPopulation II variable, shows extremely strong period changes. In threecases, secular light curve variation was discovered. The amplitude ofthe light variation as AS Per is decreasing; the other type of lightcurve variation is the variation in the steepness of the rising branch(SU Cyg, FF Aql). The effect of the orbital motion on the O-C diagram isalso investigated for FF Aql. Finally, the instability of the period fordifferent types of cepheids is discussed.
| Catalogue d'étoiles variables nouvelles
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