Photometry of Type II Cepheids. II. The Short-Period Stars
We present 668 new photometric observations for 24 Cepheids with periodsless than 3 days. Most of the stars are probable type II Cepheids, butwe have included some type I Cepheids for comparison. A discussion ofthe Fourier parameters of the light curves leads to the conclusion thatthey can be used to distinguish among the several types of light curvesfound among the type II stars but are of limited usefulness fordistinguishing between type I and type II Cepheids. The pulsationalstability is investigated by searching for long-term changes in thelight-curve shapes, period changes, and light-curve scatter. In terms ofthese parameters, the pulsation is more stable than those that werefound for the long-period stars, but for each there are several starsthat show unusually large effects. However, there does not seem to beany obvious difference in light-curve stability of type II Cepheidscompared with type I Cepheids.
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The Spectra of Type II Cepheids. I. The Hα Line in Short-Period Stars
We present 88 Hα profiles for 24 pulsating variable stars withperiods between 1 and 3 days in order to explore the behavior of thisline in type II as compared with classical Cepheids. Surprisingly, largevelocity differences were found between Hα and the metal lines insome type II Cepheids. Strong emission was observed in three stars, VZAql, NW Lyr, and V439 Oph, while line filling by incipient emission ispresent in seven others. All of the stars with emission and most withincipient emission belong to Diethelm's AHB2 class, and the emission isassociated with the secondary bump on the rising branch of the lightcurve. Two stars, BF Ser and MQ Aql, show doubling of the core nearmaximum light, and asymmetry of the line is noted in some spectra.Based in part on observations obtained with the Apache Point Observatory3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
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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.
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Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
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Period changes of AHB1 variables.
In order to investigate the period variations of AHB1 pulsatingvariables due to evolutionary effects predicted by Sandage, Diethelm andTammann (1994), the photographic Sky Survey of the SonnebergObservatory, Germany, for the years 1928-1994 was searched. Byconstructing seasonal mean light curves and using the rise-time method,it is shown that the periods of four of six field AHB1 variablesexamined (EK Del, UY Eri, CE Her, V716 Oph) have been increasing overthe last 70 years, while two stars, BF Ser and XX Vir, shows no changeof period in this interval. The rate of the period change is in goodagreement with the theoretically expected values.
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Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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Kinematics of metal-poor stars in the galaxy
We discuss the kinematic properties of a sample of 1936 Galactic stars,selected without kinematic bias, and with abundances (Fe/H) is less thanor equal to -0.6. The stars selected for this study all have measuredradial velocities, and the majority have abundances determined fromspectroscopic or narrow-/intermediate-band photometric techniques. Incontrast to previous examinations of the kinematics of the metal-poorstars in the Galaxy, our sample contains large numbers of stars that arelocated at distances in excess of 1 kpc from the Galactic plane. Thus, amuch clearer picture of the nature of the metal-deficient populations inthe Galaxy can now be drawn.
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Summary of Delta S metallicity measurements for bright RR Lyrae variables observed at Lick Observatory and KPNO between 1972 and 1987
From 1972 to 1987 we conducted a survey of the metallicity of faint RRLyrae variables in the Galactic halo, using the 'Butler system' of DeltaS. As part of the calibration of this program, we made approximately 500observations of bright RR Lyraes as abundance standards. We summarizeall the observations of these bright field RR Lyraes and provideaveraged values for the metallicity parameter Delta S. These averagesrepresent the most precise definition of the Butler system for themeasurement of RR Lyrae metallicities. The typical mean error is 0.3units in Delta S, which corresponds to 0.05 dex in (Fe/H). We alsobriefly discuss the weaknesses in the determination of (Fe/H) from DeltaS.
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The P-L relation for RR Lyrae-like stars with 0.8d less than P less than 3d
Data are summarized for 52 of the rare pulsating variables, here calledAHB1 variables for 'above horizontal branch', that have RRab Lyrae-likelight curves but periods in the range of 0.8 less than P less than 3d.The absolute magnitudes, calculated either from the pulsation equationor determined relative to the level of the globular cluster horizontalbranch, range from Mv = +0.2 to Mv = -1.4. The P-Lrelation is well defined, with a ridge-line equation of Mbol= -2.00 log P - 0.10. The standard deviation of the present sample aboutthe rigid-line is only 0.29 mag. Theoretical evolutionary tracks on theway from the ZAHB to the Asymptotic Giant Branch (AGB) conform well withthe data and show that the P-L relation for AHB1 stars is independent ofmetallicity in this period range. This is in contrast to the absolutemagnitudes of normal RR Lyraes near the horizontal branch in the periodrange from 0.4 to 0.8d, where there is a strong dependence ofMv on metallicity, also predicted by the models shown here.The rate of transversal through the instability strip is of the order of100 times faster for these stars than for the ordinary RR Lyrae starscloser to the horizontal branch, making it likely that their observedperiod changes are due to secular evolution, well above pulsation'noise'.
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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.
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Physical parameters of pulsating variables with periods between one and three days. II - Fundamental parameters
On the basis of the Walraven VBLUW photometry data reported by Diethelm(1986) on 57 pulsating variables with periods between one and threedays, primary parameters (metallicity, log g, Teff, and the amount ofreddening) were deduced for 11 of these stars, using a semiempiricalapproach based on model atmosphere calculations. Results indicate thatboth the C-delta and the SA-class of the pulsating variables are youngstars of the disc-population pulsating either in the fundamental(C-delta) or in the first overtone mode (SA). The AHB1 stars, whichshowed a marked deficiency in metal abundance, are members of the halopopulaton. The stars of the AHB2 and AHB3 groups, which show anintermediate metallicity, must be considered as members of anintermediate stellar population.
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Studies of Cepheid-type variability. V - The Fourier phases of type II Cepheids with periods of 1-3 days
Fourier phases of type II Cepheids with periods 1-3 d are reanalyzed andcompared with similar data for classical Cepheids, using a new phasedefinition recently proposed by Stellingwerf and Donohoe (1986). It isfound that this definition allows an improved analysis, mainly due tothe possibility of comparison with a standard case. It is shown that theavailable data for the type II Cepheids are in good agreement with theassumption of a resonance at a period of about 1.5 d.
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Population studies. II - Kinematics as a function of abundance and galactocentric position for (Fe/H) of -0.6 or less
A catalog is presented of some 1200 Galactic objects which have radialvelocities and (Fe/H) abundances of -0.6 or less. These data areanalyzed to yield information on the kinematic properties of the olderpopulations of the Galaxy and on the interdependence between kinematicsand abundance. It is found that the kinematics of the availablekinematically selected stars differ from those of the nonkinematicallyselected objects. No evidence is found for any significant difference inthe kinematic properties of the various halo subgroups, nor for anydependence of kinematics on abundance. While the rotation of the halo issmall at about 37 km/s for (Fe/H) of -1.2 or less, it rises quickly forhigher abundances to a value of about 160 km/s at (Fe/H) = 0.6. Objectsin the abundance range -0.9 to -0.6 appear to belong predominantly to apopulation possessing the kinematic characteristics of a thick disk. Theimplications of these findings for the suggestion that globular clustersbelong to the same population as the noncluster objects, for the originof the thick disk, and for the mass of the Galaxy are discussed.
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Studies of Cepheid-type variability. III - Fourier description of light curves of Type II Cepheids of periods 1-3 days
Abstract image available at:http://adsabs.harvard.edu/abs/1986A&A...156..337P
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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.
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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.
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A photometric classification of pulsating variables with periods between one and three days
Available photometric (2000 UBV measurements) data were employed toestablish standard classifications of Cepheid variables. The datacovered pulsating variables in the Galaxy with periods between 1-3 days.The V lightcurves revealed that the 28 variables in the surveys could beclassified into four groups. The RR Lyrae stars have a smooth Vlightcurve, a short rise time, and a large amplitude in B(AB). The WVirginis stars exhibit a pronounced brightness hump on the ascendingbranch 0.2 h before brightness maximum, while BL Herculis stars have ahump on the descending branch, with rise times decreasing withincreasing periods. Finally, classical Cepheids have a smooth variationwith a gradual rise to maximum. All lie within 3 deg of the galacticequator. The UBV measurements are concluded to be suitable for a coarseseparation of populations of stars.
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BL Herculis stars - Theoretical models for field variables
Type II Cepheids with periods between 1 and 3 days, commonly designatedas Bl Herculis stars, have been modeled here with the aim ofinterpreting the wide variety of light curves observed among the fieldvariables. Previously modeled globular cluster members are used asstandard calibration objects. The major finding is that only a smallrange of luminosities is capable of generating a large variety of lightcurve types at a given period. For a mass of approximately 0.60 solarmass, the models are able to reproduce the observed mean luminosities,dispersion of mean luminosities, periods, light amplitudes, lightasymmetries, and phases of secondary features in the light curves ofknown BL Her stars. It is possible that the metal-rich variables (whichare found only in the field) have luminosities lower than those of mostmetal-poor variables. The present revised mass for BL Her, a metal-richobject, is not significantly different from the mean mass of themetal-poor variables.
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Photoelectric Photometry of Cepheid Variables with Periods Between One and Three Days
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982A&AS...47..335D&db_key=AST
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Photometric abundances of Type II Cepheid variables
Washington-system colors and V magnitudes of 63 Type II Cepheids areused to investigate the distribution of metal abundances in these starsand correlations of their abundances with position in the Galaxy. Only asmall fraction of Cepheids in the field represent a true halopopulation; most have characteristics of a transition population betweenthe halo and the disk. The origin of the metal-rich stars and theirrelation to the metal-rich RR Lyraes is discussed. The abundancedistribution of all Type II Cepheids shows no strong dependence ondistance from the galactic center.
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Photoelectric UBV observations of RR Lyrae variable stars, second list.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977RMxAA...2..235B&db_key=AST
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Absolute magnitudes and motions of RR Lyrae stars
Absolute magnitudes are found by the use of statistical parallax for RRLyrae stars which have been grouped by period and by metal type. TheBailey c-type stars are treated independently. Solar motion solutionsare made using velocity data. Parameters of galactic orbits obtainedfrom space velocities show a relation to period. For the total a-stargroup the resultant mean light visual absolute magnitude is 0.49 mag,which corresponds to MB of 0.63 mag. Using this figure, thedistance to the galactic center is 9.3 kpc.
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Intrinsic colours and absolute magnitudes of 32 halo population cepheids with periods from one to two days.
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Elements of 16 pulsating variable stars.
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Proper motions, mean parallaxes and space velocities of RR Lyrae variables
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A Spectroscopic Study of the RR Lyrae Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1959ApJ...130..507P&db_key=AST
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Stars with Incomplete Observational Data and with Possible Hyperbolic Velocities
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Radial Velocities of 15 RR Lyrae Variables
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BF SER : a pulsating variable with an unusual period.
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162 neue Veräderliche
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INHABITED SKY
