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Radial Velocities of RR Lyrae Stars
We report 84 radial velocities for 36 field RR Lyrae variable stars. Thetypical uncertainty of a single velocity is estimated at +/-0.5 kms-1. Our sample consists of variables with insufficientpre-existing data for reliable center-of-mass radial velocitydeterminations. We have computed center-of-mass velocities from our newvelocities using RR Lyr velocity templates. The center-of-mass radialvelocities have a typical uncertainty of +/-1.5 km s-1 forvariables observed at least three times.
| Variable Stars in NSVS Database I. 86 New Variables in Andromeda
A search for light curves with variability in the NSVS data was carriedout in a 46 square-degree area in Andromeda. The field contains 51955light curves. We found 136 variables, 86 of them were not knownpreviously. Extrapolating the density of the variables in the field tothe whole NSVS, the total number of variables in the survey is estimatedto be 52000 - 61000.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| The triple-mode pulsating variable V823 Cassiopeiae
Using extended multicolour CCD photometry of the triple-mode radialpulsator V823 Cas we studied the properties of the coupling frequenciesinvoked by nonlinear processes. Our results support that a resonanceconnection affects the mode coupling behaviour. The P1/P0 period ratioof V823 Cas has an “out of range” value if compared with theperiod ratios of the known double mode pulsators, while the P2/P1 periodratio is normal. The periods and period ratios cannot be consistentlyinterpreted without conflict with pulsation and/or evolution models. Wedescribe this failure with the suggestion that at present, the periodsof V823 Cas are in a transient, resonance affected state, thus do notreflect the true parameters of the object. The anomalous period changebehaviour of the fundamental and second overtone modes supports thisidea. We have also raised the possibility that a f0+f2 = 2f1 resonance may act in triple modepulsators.
| uvby-beta photometry of the RR Lyrae star AC And .
In the present paper we determine the true nature of AC And an RR Lyraeor delta Scuti star and its physical parameters from multi-colorphotometry.
| uvby-β Photometry of the RR Lyrae Star AC And
Strömgren uvby-β and differential V photoelectric photometryof the variable star AC And is presented. Analysis of this data, as wellas data from the literature, corroborates the periods proposed by Fitch& Szeidl (1976). Strömgren photometry has been used for thedetermination of the reddening and the physical parameters log g and logTe, as well as the metallicity [Fe/H]. The determination ofMv is also discussed and, in view of the results, we proposethat AC And is an RR Lyrae star with possible anomalous chemicalcomposition.
| Seismology of triple-mode classical Cepheids of the Large Magellanic Cloud
We interpret the three periods detected in OGLE LMCCepheids SC3-360128 and SC5-338399as corresponding to the first three overtones of radial pulsations. Thisinterpretation imposes stringent constraints on parameters of the starsand on their evolutionary status, which could only be the first crossingof the instability strip. Evolutionary models reproducing measuredperiods exist only in a restricted range of metallicities (Z=0.004 {-}0.007). The models impose an upper limit to the extent of overshootingfrom the convective core. Absolute magnitude of each star is confined toa narrow interval, which allows us to derive a new estimate of thedistance to the LMC. We obtain the value of m-Mranging from 18.34 m to 18.53 m with a systematic difference between thetwo stars of about 0.13 m. The rates of period change predicted by themodels are formally in conflict with the derived observational limits,though the uncertainties of measured dot{P} may have beenunderestimated. If this discrepancy is confirmed, it would constitute asignificant challenge to the stellar evolution theory.
| AC And mit mehrfachen Schwingungen.
Not Available
| System Description and First Light Curves of the Hungarian Automated Telescope, an Autonomous Observatory for Variability Search
Having been operational at Kitt Peak for more than a year, the prototype(HAT-1) of the Hungarian Automated Telescope (HAT) has been used for anall-sky variability search of the northern hemisphere. This smallautonomous observatory is recording the brightness of stars in the rangeof IC~6-13 mag with a telephoto lens and its9deg×9deg field of view, yielding a datarate of ~106 photometric measurements per night. We givebrief hardware and software descriptions of the system, controlled by asingle PC running RealTime Linux OS. We provide an overview ofsite-specific details and quantify the astrometric and photometriccapabilities of HAT. As a demonstration of system performance, we give asample of 60 short-period variables in a single selected field, allbright, with I<13 mag, where only 14 were known before. Depending onthe observing strategy, a search for extrasolar planet transits is alsoa feasible observing program. We conclude with a short discussion onfuture directions. Further information can be found at the HAT Webpage.3
| On the relationship between the δ Scuti and γ Doradus pulsators
We searched for δ Scuti-type pulsations amongst known andcandidate γ Doradus stars. The motivations for such a project comefrom the need to understand the relationship of these two classes ofpulsator better, from the present poor knowledge of the hot border ofthe γ Doradus phenomenon, and from the exciting prospects forasteroseismology should stars be found which have both types ofpulsation excited. We acquired 270h of observations and monitored atotal of 26 stars. One target, HD 209295, turned out to be a member ofboth classes of pulsating star, but this object is peculiar in the sensethat it is a close binary. We classify six of our targets as new bonafide γ Doradus stars, whereas nine more are good γ Doraduscandidates, and three turned out to be ellipsoidal variables. One of ourprogramme stars was found to be a δ Scuti star, with no additionalγ Doradus variations. Furthermore, one star was already known tobe a bona fide γ Doradus star, and we could not find anunambiguous explanation for the variability of five more stars. Theanalysis of our data together with improved knowledge of stars from theliterature enabled us to revise the blue border of the γ Doradusphenomenon towards cooler temperatures. This new blue edge is muchbetter defined than the previous one and extends from a temperature ofabout 7550K on the ZAMS to 7400K one magnitude above it. Five bona fideγ Doradus stars we observed are located inside the δ Scutiinstability strip, but none of them exhibited observable δ Scutipulsations. We therefore suggest that γ Doradus stars are lesslikely to be δ Scuti pulsators compared with other normal stars inthe same region of the lower instability strip. In addition, we showthat there is a clear separation between the pulsation constants Q ofδ Scuti and γ Doradus stars. The γ Doradus stars knownto date all have Q>0.23d.
| Physical Parameter Determination of the δ Scuti Star V1719 Cygni
New uvbyβ photoelectric photometry of the short-period variablestar V1719 Cygni (HD 200925) has been secured. A period analysis ofthese data and those reported in the literature has provided us withstable pulsation frequencies that fit all the available observationscovering a time span of 20 yr. The frequencies determined are 3.7411556,7.4823111, 11.2234667, and 4.6777749 cycles day-1 and ofsmaller amplitude 8.4189900 cycles day-1. It was found thatthis Population I star has logg around 3.1 and an effective temperatureof 6750 K.
| The Intermediate-Period Cepheid Strip Stars
To explore the population of variable stars that fall between RR Lyraestars and classical Cepheids, we have obtained extensive photometricobservations for 56 stars with periods between 0.6 and 1.0 days. Forthese stars and an additional 10, we have examined the form andstability of the light curves to explore the variety of types of starsin this period regime. We conclude that the majority of the sample areBailey type ab RR Lyrae stars. However, a surprising number thatpossibly exhibit the Blazhko effect are found. There are a half-dozenother stars that do not appear to be in either of these two groups. Oneis the well-known multimode pulsator AC And. We suggest that two of theothers may be anomalous Cepheids and two may be type II Cepheids.
| Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
A selection criterion based on the relative strength of the largestpeaks in the amplitude spectra, and an information criterion are used incombination to search for multiperiodicities in Hipparcos epochphotometry. The method is applied to all stars which have beenclassified as variable in the Hipparcos catalogue: periodic, unsolvedand microvariables. Results are assessed critically: although there aremany problems arising from aliasing, there are also a number ofinteresting frequency combinations which deserve further investigation.One such result is the possible occurrence of multiple periods of theorder of a day in a few early A-type stars. The Hipparcos catalogue alsocontains a number of these stars with single periodicities: such starswith no obvious variability classifications are listed, and informationabout their properties (e.g., radial velocity variations) discussed.These stars may constitute a new class of pulsators.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| delta Scuti and related stars: Analysis of the R00 Catalogue
We present a comprehensive analysis of the properties of the pulsatingdelta Scuti and related variables based mainly on the content of therecently published catalogue by Rodríguez et al.(\cite{retal00a}, hereafter R00). In particular, the primaryobservational properties such as visual amplitude, period and visualmagnitude and the contributions from the Hipparcos, OGLE and MACHOlong-term monitoring projects are examined. The membership of thesevariables in open clusters and multiple systems is also analyzed, withspecial attention given to the delta Scuti pulsators situated ineclipsing binary systems. The location of the delta Scuti variables inthe H-R diagram is discussed on the basis of HIPPARCOS parallaxes anduvbybeta photometry. New borders of the classical instability arepresented. In particular, the properties of the delta Scuti pulsatorswith nonsolar surface abundances (SX Phe, lambda Boo, rho Pup, delta Deland classical Am stars subgroups) are examined. The Hipparcos parallaxesshow that the available photometric uvbybeta absolute magnitudecalibrations by Crawford can be applied correctly to delta Scutivariables rotating faster than v sin i ~ 100 km s{-1} withnormal spectra. It is shown that systematic deviations exist for thephotometrically determined absolute magnitudes, which correlate with vsin i and delta m1. The photometric calibrations are found tofit the lambda Boo stars, but should not be used for the group ofevolved metallic-line A stars. The related gamma Dor variables and thepre-main-sequence delta Scuti variables are also discussed. Finally, thevariables catalogued with periods longer than 0fd 25 are examined on astar-by-star basis in order to assign them to the proper delta Scuti, RRLyrae or gamma Dor class. A search for massive, long-period delta Scutistars similar to the triple-mode variable AC And is also carried out.
| 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.
| 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.
| Kinematics of Metal-poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Nonkinematically Selected Stars
We present a detailed analysis of the space motions of 1203solar-neighborhood stars with metal abundances [Fe/H]<=-0.6, on thebasis of a catalog, of metal-poor stars selected without kinematic biasrecently revised and supplemented by Beers et al. This sample, havingavailable proper motions, radial velocities, and distance estimates forstars with a wide range of metal abundances, is by far the largest suchcatalog to be assembled to date. We show that the stars in our samplewith [Fe/H]<=-2.2, which likely represent a ``pure'' halo component,are characterized by a radially elongated velocity ellipsoid(σU,σV,σW)=(141+/-11,106+/-9, 94+/-8) km s-1 and small prograde rotation=30 to 50 km s-1, consistent withprevious analysis of this sample by Beers and Sommer-Larsen based onradial velocity information alone. In contrast to the previous analysis,we find a decrease in with increasingdistance from the Galactic plane for stars that are likely to be membersof the halo population(Δ/Δ|Z|=-52+/-6 km s-1kpc-1), which may represent the signature of a dissipativelyformed flattened inner halo. Unlike essentially all previouskinematically selected catalogs, the metal-poor stars in our sampleexhibit a diverse distribution of orbital eccentricities, e, with noapparent correlation between [Fe/H] and e. This demonstrates, clearlyand convincingly, that the evidence offered in 1962 by Eggen,Lynden-Bell, & Sandage for a rapid collapse of the Galaxy, anapparent correlation between the orbital eccentricity of halo stars withmetallicity, is basically the result of their proper-motion selectionbias. However, even in our nonkinematically selected sample, we haveidentified a small concentration of high-e stars at [Fe/H]~-1.7, whichmay originate, in part, from infalling gas during the early formation ofthe Galaxy. We find no evidence for an additional thick disk componentfor stellar abundances [Fe/H]<=-2.2. The kinematics of theintermediate-abundance stars close to the Galactic plane are, in part,affected by the presence of a rapidly rotating thick disk component with ~=200 km s-1 (with a verticalvelocity gradient on the order ofΔ/Δ|Z|=-30+/-3 km s-1kpc-1) and velocity ellipsoid (σU,σV, σW)=(46+/-4, 50+/-4, 35+/-3) kms-1. The fraction of low-metallicity stars in the solarneighborhood that are members of the thick disk population is estimatedas ~10% for -2.2<[Fe/H]<=-1.7 and ~30% for -1.7<[Fe/H]<=-1.We obtain an estimate of the radial scale length of the metal-weak thickdisk of 4.5+/-0.6 kpc. We also analyze the global kinematics of thestars constituting the halo component of the Galaxy. The outer part ofthe halo, which we take to be represented by local stars on orbitsreaching more than 5 kpc from the Galactic plane, exhibits no systematicrotation. In particular, we show that previous suggestions of thepresence of a ``counter-rotating high halo'' are not supported by ouranalysis. The density distribution of the outer halo is nearly sphericaland exhibits a power-law profile that is accurately described asρ~R-3.55+/-0.13. The inner part of the halo ischaracterized by a prograde rotation and a highly flattened densitydistribution. We find no distinct boundary between the inner and outerhalo. We confirm the clumping in angular-momentum phase space of a smallnumber of local metal-poor stars noted in 1999 by Helmi et al. We alsoidentify an additional elongated feature in angular-momentum phase spaceextending from the clump to regions with high azimuthal rotation. Thenumber of members in the detected clump is not significantly increasedfrom that reported by Helmi et al., even though the total number of thesample stars we consider is almost triple that of the previousinvestigation. We conclude that the fraction of halo stars that may havearisen from the precursor object of this clump may be smaller than 10%of the present Galactic halo, as previously suggested. The implicationsof our results for the formation of the Galaxy are discussed, inparticular in the context of the currently favored cold dark mattertheory of hierarchical galaxy formation.
| The Nature of V829 Aql - A Triple-Mode Radially Pulsating Post-Main-Sequence Delta Scuti Star
Not Available
| V829 Aquilae is a Pulsating Star with a Variable Light Curve
Not Available
| 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.
| The MACHO project LMC variable star inventory. 1: Beat Cepheids-conclusive evidence for the excitation of the second overtone in classical Cepheids
We report the discovery of 45 beat Cepheids in the Large MegellanicCloud (LMC) using the Massive Compact Halo Object (MACHO) shown to breakcleanly into two period-ratio groups, providing the first unambiguousevidence that the second overtone is indeed excited in Cepheids. 30stars are beating in the fundamental and first overtone mode (F/1H, witha period ratio in the neighborhood of 0.72), and 15 stars are beating inthe first and second overtone (1H/2H, with a period ratio near 0.80).The F/1H period ratios are systematically higher than known Galacticbeat Cepeids, indicating a metallicity dependence whose sense is inagreement with theory. Beat Cepheids in the LMC are found to select the1H/2H mode for principal periods shorter than 1.25 days. We find thefraction of Cepheids excited in two modes to be about 20% for stars withfundamental periods shorter than 2.5 days. We fail to confirm any of theproposed beat Cepheid candidates common to our sample from the surveysof Andreasen (1987) and Andreasen & Petersen (1987). We also presentfinder charts and find several of the beat Cepheids to be in or near LMCclusters. In addition, we find three double Cepheids -unresolved pairsof Cepheids which may be physically related.
| 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.
| AC Andromedae: the missing link between δ Scuti stars and classical Cepheids?
Abstract image available at:http://adsabs.harvard.edu/abs/1994MNRAS.271L..19F
| The triple-mode variable AC Andromedae
We have calculated a large number of linear radial pulsation models tofit the periods of AC And. In the parameter regime representative of RRLyrae stars no models can be found that match the observed periods forany heavy element abundance Z. There are, however, two groups of highermass models which yield complete agreement between the observed periodsand those of the first three radial modes. The first comprises modelswith 0.001 less than Z less than 0.002 and masses and luminosities of1.1 less than M/solar mass less than 1.4, 100 less than L/solarluminosity less than 130 (depending on Z). The second group has highermasses, luminosities and Z, viz. 0.01 less than Z less than 0.02,M/solar mass approximately 2.7, 80 less than L/solar luminosity lessthan 200. These ranges are sensitive to the assumed uncertainties of themodel periods. We give ranges of model parameters as functions of Z anddiscuss their uncertainties. Present observational constraints and thelimited sensitivity of the method of fitting periods do not allow us tosufficiently narrow down the derived parameter ranges. Furthermore,although recent evolution calculations are in fair agreement with bothlow- and high-mass models, the latter ones are preferred because thetheoretical period changes are in better agreement with theobservations. Therefore, we suggest that AC And is an evolved high-massstar, with similarities to the delta Scuti type stars, or perhaps a rareoddball. As a side product of our survey, we give accurate fittingformulae for the periods and period ratios.
| Light curves of the three-mode RR Lyrae-type star AC Andromeda
Separate light curves are constructed for each oscillation of thetriple-mode RR Lyrae star AC And. The nonlinearity of the interaction ofthe three modes is exhibited in the strong form variations of the lightcurves of all three oscillations; specifically, the maximum amplitude ofeach oscillation is observed when the two remaining ones are nearmaximum, and the minimum amplitude is observed when they are nearminimum. The nature of the mode interaction in AC And is the same as indouble mode Cepheids.
| Infrared photometry and radial velocities of field RR Lyraes
Infrared photometry of 110 field RR Lyraes is presented along withradial velocities of 13 field RR Lyraes. The methods used are described.
| Studies of Cepheid-type variability. VII - Stellar opacities and multimode Cepheid variables
Until now the most attractive explanation for the discrepant periodratios of double mode bariable stars has been the hypothesis ofincreased metal opacities. Here the unique variable stars HR 6522 and ACAndromedae and three further double mode variable stars are used to testthis hypothesis. The data for AC And are in good agreement with thehypothesis, but the additional tests are inconclusive. It is suggestedthat observed period ratios 0.82-0.84, usually taken as evidence fornon-radial oscillations, may in fact indicate radial oscillations in thesecond and third overtones.
| A search for double-mode RR Lyrae stars in M3
Photometric observations obtained between 1895 and 1962 are used tosystematically search for double mode RR Lyrae (RRd) stars in M3. Of the46 stars considered, only V68 and V87 (both of which were previouslyidentified as double-mode pulsators) are shown to be certain RRdvariables. Masses of 0.52 + or - 0.005 solar masses for V68 and 0.55 +or - 0.015 solar masses for V87 are obtained, confirming the suggestionthat RRd stars in Oosterhoff Type I systems are systematically 20percent less massive, and correspondingly less luminous, than RRd starsin Oosterhoff Type II systems. Although evidence is found forcycle-to-cycle light variations, no significant long-term amplitudechanges were noted.
| 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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