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A catalogue of RR Lyrae stars from the Northern Sky Variability Survey
A search for RR Lyrae stars has been conducted in the publicly availabledata of the Northern Sky Variability Survey. Candidates have beenselected by the statistical properties of their variation; the standarddeviation, skewness and kurtosis with appropriate limits determined froma sample 314 known RRab and RRc stars listed in the General Catalogue ofVariable Stars. From the period analysis and light-curve shape of over3000 candidates 785 RR Lyrae have been identified of which 188 arepreviously unknown. The light curves were examined for the Blazhkoeffect and several new stars showing this were found. Six double-mode RRLyrae stars were also found of which two are new discoveries. Somepreviously known variables have been reclassified as RR Lyrae stars andsimilarly some RR Lyrae stars have been found to be other types ofvariable, or not variable at all.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| The GEOS RR Lyr Survey
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| The GEOS RR Lyr Survey
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| Spectroscopy of QUEST RR Lyrae Variables: The New Virgo Stellar Stream
Eighteen RR Lyrae variables (RRLs) that lie in the ``12.4h clump''identified by the Quasar Equatorial Survey Team (QUEST) have beenobserved spectroscopically to measure their radial velocities and metalabundances. Ten blue horizontal branch (BHB) stars identified by theSloan Digital Sky Survey (SDSS) were added to this sample. Six of thenine stars in the densest region of the clump have a mean radialvelocity in the Galactic rest frame (Vgsr) of 99.8 andσ=17.3 km s-1, which is slightly smaller than theaverage error of the measurements. The whole sample contains eight RRLsand five BHB stars that have values of Vgsr suggestingmembership in this stream. For seven of these RRLs, the measurements of[Fe/H], which have an internal precision of 0.08 dex, yield<[Fe/H]>=-1.86 and σ=0.40. These values suggest that thestream is a tidally disrupted dwarf spheroidal galaxy of low luminosity.Photometry from the database of the SDSS indicates that this streamcovers at least 106 deg2 of the sky in the constellationVirgo. The name Virgo stellar stream is suggested.
| TY Gruis: A Metal-Poor Carbon and Neutron-Capture-Rich RR Lyrae Star
We have conducted a photometric and high-resolution spectroscopicanalysis of the high-latitude (l=1deg, b=-55deg)metal-poor RR Lyrae star TY Gru (=CS 22881-071). We find this star tohave large overabundances of carbon and neutron-capture elements. Masstransfer from an asymptotic giant branch binary companion prior to itsRR Lyrae evolutionary state is the simplest explanation of thiscircumstance. Unfortunately, TY Gru is afflicted by the Blazhko effect,which greatly complicates accurate measurement of the motion of itscenter of mass. We have not yet detected the small orbital motion thatwould be produced by a distant degenerate companion of TY Gru.This paper includes data gathered with the 6.5 m Magellan Telescopeslocated at Las Campanas Observatory, Chile.
| [Fe/H] derived from the light curves of RR Lyrae stars in the Galactic halo
Context: .The iron abundance of halo RR Lyrae stars can provideimportant information about the formation history of the Galactichalo. Aims: .We determine the [Fe/H] of the sample of halo RRabstars by using the P-ϕ31-[Fe/H] relation developed byJurcsik & Kovács based on their light curves. We need toextend the relation from the V band to our unfiltered CCD band. Methods: .To do this, we use the low-dispersion spectroscopic [Fe/H] ofliteratures and the photometric data released by the first-generationRobotic Optical Transient Search Experiment (ROTSE-I) project. We doregression analyses for the calibrating sample using a linear functionand test its validity by comparing of the predicted [Fe/H] with thespectroscopic [Fe/H]. In general, the fit accuracy for the two different[Fe/H] is better than 0.19 dex. Results: . We derive an empiricalP-ϕ31-[Fe/H] linear relation for the unfiltered CCD band(ROTSE-I), i.e. [ Fe/H]=-3.766-5.350P+1.044ϕ31. In ourtest, the P-ϕ31-[Fe/H] relation is also fit for ourunfiltered CCD band. In addition, another linear relation,ϕ31_V=0.882+0.792ϕ31_W, is also derivedfor the transformation between the V and W bands. We present thepredicted [Fe/H] of the sample (the 31 halo RRab stars) in a catalog. Conclusions: . The mean [Fe/H] of the sample is -1.63 with dispersionof 0.45 dex in distribution, which is consistent with the resultsderived from the blue horizontal branch star candidates by Kinnman etal. (2000, A&A, 364, 102). The mean [Fe/H] values of the RRab starsin the range of 1 kpc, 2 kpc, and 3 kpc from the star 91 (a double-modeRR Lyrae star), are all lower than that of the background halo stars.These values are consistent with that of star 91 suggested by Wu et al.(2005, AJ, 130, 1640), which indicates they might have a common origin.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| The GEOS RR Lyr Survey
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| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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| VLT Spectroscopy of RR Lyrae Stars in the Sagittarius Tidal Stream
Sixteen RR Lyrae variables from the QUEST survey that lie in the leadingarm of the tidal stream from the Sagittarius dSph galaxy have beenobserved spectroscopically to measure their radial velocities and metalabundances. The systemic velocities of 14 stars, which were determinedby fitting a standard velocity curve to the individual measurements,have a sharply peaked distribution with a mean of 33 km s-1and a standard deviation of only 25 km s-1. The [Fe/H]distribution of these stars has a mean of -1.76 and a standard deviationof 0.22. These measurements are in good agreement with previous onesfrom smaller samples of stars. The mean metallicity is consistent withthe age-metallicity relation that is observed in the main body of theSgr dSph galaxy. The radial velocities and the distances from the Sun ofthese stars are compared with recent numerical simulations of the Sgrstreams that assume different shapes for the dark matter halo. Modelsthat assume a oblate halo do not fit the data as well as ones thatassume a spherical or a prolate distribution. However, none of the fitsare completely satisfactory. Every model fails to reproduce the longextent of the stream in right ascension (36°) that is seen in theregion covered by the QUEST survey. Further modeling is required to seeif this and the other mismatches between theory and observation can beremoved by judicial choices for the model parameters or instead rule outa class of models.
| Proper identification of RR Lyrae stars brighter than 12.5 mag
RR Lyrae stars are of great importance for investigations of Galacticstructure. However, a complete compendium of all RR-Lyraes in the solarneighbourhood with accurate classifications and coordinates does notexist to this day. Here we present a catalogue of 561 local RR-Lyraestars (V_max ≤ 12.5 mag) according to the magnitudes given in theCombined General Catalogue of Variable Stars (GCVS) and 16 fainter ones.The Tycho2 catalogue contains ≃100 RR Lyr stars. However, manyobjects have inaccurate coordinates in the GCVS, the primary source ofvariable star information, so that a reliable cross-identification isdifficult. We identified RR Lyrae from both catalogues based on anintensive literature search. In dubious cases we carried out photometryof fields to identify the variable. Mennessier & Colome (2002,A&A, 390, 173) have published a paper with Tyc2-GCVSidentifications, but we found that many of their identifications arewrong.
| RR Lyrae stars: kinematics, orbits and z-distribution
RR Lyrae stars in the Milky Way are good tracers to study the kinematicbehaviour and spatial distribution of older stellar populations. Arecently established well documented sample of 217 RR Lyr stars withV<12.5 mag, for which accurate distances and radial velocities aswell as proper motions from the Hipparcos and Tycho-2 catalogues areavailable, has been used to reinvestigate these structural parameters.The kinematic parameters allowed to calculate the orbits of the stars.Nearly 1/3 of the stars of our sample have orbits staying near the MilkyWay plane. Of the 217 stars, 163 have halo-like orbits fulfilling one ofthe following criteria: Θ < 100 km s-1, orbiteccentricity >0.4, and normalized maximum orbital z-distance>0.45. Of these stars roughly half have retrograde orbits. Thez-distance probability distribution of this sample shows scale heightsof 1.3±0.1 kpc for the disk component and 4.6±0.3 kpc forthe halo component. With our orbit statistics method we found a(vertical) spatial distribution which, out to z=20 kpc, is similar tothat found with other methods. This distribution is also compatible withthe ones found for blue (HBA and sdB) halo stars. The circular velocityΘ, the orbit eccentricity, orbit z-extent and [Fe/H] are employedto look for possible correlations. If any, it is that the metal poorstars with [Fe/H] <1.0 have a wide symmetric distribution aboutΘ=0, thus for this subsample on average a motion independent ofdisk rotation. We conclude that the Milky Way possesses a halo componentof old and metal poor stars with a scale height of 4-5 kpc having randomorbits. The presence in our sample of a few metal poor stars (thus partof the halo population) with thin disk-like orbits is statistically notsurprising. The midplane density ratio of halo to disk stars is found tobe 0.16, a value very dependent on proper sample statistics.
| The GEOS RR Lyr Survey
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| RR Lyrae Sterne und ihre Bahnen in der Galaxis.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
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| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| The Metallicity Dependence of the Fourier Components of RR Lyrae Light Curves Is the Oosterhoff-Arp-Preston Period Ratio Effect in Disguise
The correlation of particular Fourier components of the light curves ofRR Lyrae variables with metallicity, discovered by Simon and later byKovacs and his coworkers, is shown to have the same explanation as theperiod ratios (period shifts in logP) between RRab Lyrae variables thathave the same colors, amplitudes, and light-curve shapes but differentmetallicities. A purpose of this paper is to demonstrate that the modelthat predicts the period-metallicity relations in the mediatingparameters of colors, amplitudes, and light-curve shapes also explainsthe Simon-Kovacs et al. correlation between period, φ31,and metallicity. The proof is made by demonstrating that the combinationof the first- and third-phase terms in a Fourier decomposition of RRablight curves, called φ31 by Simon & Lee, variesmonotonically across the RR Lyrae instability strip in the same way thatamplitude, color, and rise time vary with period within the strip. Thepremise of the model is that if horizontal branches at the RR Lyraestrip are stacked in luminosity according to the metallicity, then therenecessarily must be a logperiod shift between RR Lyrae stars withdifferent metallicities at the same φ31 values. However,there are exceptions to the model. The two metal-rich globular clustersNGC 6388 and NGC 6441, with anomalously long periods of their RR Lyraestars for their amplitudes, violate the period-metallicity correlationsboth in amplitudes and in φ31 values (for NGC 6441 whereφ31 data exist). The cause must be related to theanomalously bright horizontal branches in these two clusters for theirmetallicities. The effect of luminosity evolution away from the zero-agehorizontal branch, putatively causing noise in the metallicity equation,is discussed. It is clearly seen in the amplitude-period correlationsbut apparently does not exist in the φ31-periodcorrelation in the data for the globular cluster M3 analyzed by Jurcsikand coworkers and by Cacciari and Fusi Pecci, for reasons not presentlyunderstood. Clarification can be expected from study of precisionphotometric data of evolved RR Lyrae stars in globular clusters ofdifferent metallicity when their Fourier components are known.
| A pulsational approach to near-infrared and visual magnitudes of RR Lyr stars
In this paper, we present an improved theoretical scenario concerningnear-infrared and visual magnitudes of RR Lyr variables, as based onup-to-date pulsating models. New relations connecting V and K absolutemagnitudes with periods, mass, luminosity and metal content arediscussed separately for fundamental and first-overtone pulsators. Wealso show that the V-K colours are predicted to supply tight constraintson the pulsator intrinsic luminosity. On this basis, we revisit the caseof the prototype variable RR Lyr, showing that the parallax inferred bythis new pulsational approach appears in close agreement with HubbleSpace Telescope absolute parallax. Moreover, available K and Vmeasurements for field and cluster RR Lyr variables with known reddeningand metal content are used to derive a relation connecting the Kabsolute magnitude to period and metallicity (MK-[Fe/H]-logP)as well as a new calibration of the MV-[Fe/H] relation. Thecomparison between theoretical prescriptions and observations suggeststhat RR Lyr stars in the field and in galactic globular clusters (GGCs)should have quite similar evolutionary histories. The comparison betweentheory and observations also discloses a general agreement that supportsthe reliability of the current pulsational scenario. On the contrary,current empirical absolute magnitudes based on the Baade-Wesselink (BW)method suggest relations with a zero-point which is fainter than ispredicted by pulsation models, together with a milder metallicitydependence. However, preliminary results based on a new calibration ofthe BW method provided by Cacciari et al. (2000) for RR Cet and SW Andappear in a much better agreement with the pulsational predictions.
| Consistent distances from Baade-Wesselink analyses of Cepheids and RR Lyraes
By using the same algorithm in the Baade-Wesselink analyses of GalacticRR Lyrae and Cepheid variables, it is shown that, within 0.03-mag1σ statistical error, they yield the same distance modulus for theLarge Magellanic Cloud. By fixing the zero-point of thecolour-temperature calibration to those of the current infrared fluxmethods and using updated period-luminosity-colour relations, we get anaverage value of 18.55 for the true distance modulus of the LMC.
| Zur qualitat der visuellen Beobachtung kurzperiodisch Veranderlicher.
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| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
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| Times of Light Maxima of Some RRab Stars
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| BAV-Beobachtungen an Programmsternen des Typs RR-Lyrae von 1951 bis 2001.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
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| Subsystems of RR Lyrae Variable Stars in Our Galaxy
We have used published, high-accuracy, ground-based and satelliteproper-motion measurements, a compilation of radial velocities, andphotometric distances to compute the spatial velocities and Galacticorbital elements for 174 RR Lyrae (ab) variable stars in the solarneighborhood. The computed orbital elements and published heavy-elementabundances are used to study relationships between the chemical,spatial, and kinematic characteristics of nearby RR Lyrae variables. Weobserve abrupt changes of the spatial and kinematic characteristics atthe metallicity [Fe/H]≈-0.95 and also when the residual spatialvelocities relative to the LSR cross the critical value V res≈290km/s. This provides evidence that the general population of RR Lyraestars is not uniform and includes at least three subsystems occupyingdifferent volumes in the Galaxy. Based on the agreement between typicalparameters for corresponding subsystems of RR Lyrae stars and globularclusters, we conclude that metal-rich stars and globular clusters belongto a rapidly rotating and fairly flat, thick-disk subsystem with a largenegative vertical metallicity gradient. Objects with larger metaldeficiencies can, in turn, be subdivided into two populations, but usingdifferent criteria for stars and clusters. We suggest that field starswith velocities below the critical value and clusters with extremelyblue horizontal branches form a spherical, slowly rotating subsystem ofthe protodisk halo, which has a common origin with the thick disk; thissubsystem has small but nonzero radial and vertical metallicitygradients. The dimensions of this subsystem, estimated from theapogalactic radii of orbits of field stars, are approximately the same.Field stars displaying more rapid motion and clusters with redderhorizontal branches constitute the spheroidal subsystem of the accretedouter halo, which is approximately a factor of three larger in size thanthe first two subsystems. It has no metallicity gradients; most of itsstars have eccentric orbits, many display retrograde motion in theGalaxy, and their ages are comparatively low, supporting the hypothesisthat the objects in this subsystem had an extragalactic origin.
| BVI Time-Series Data of the Galactic Globular Cluster NGC 3201. I. RR Lyrae Stars
We present Johnson BV- and Kron-Cousins I-band time-series datacollected over three consecutive nights in a region of 13arcmin2 centered on the Galactic globular cluster (GGC) NGC3201. The time sampling of current CCD data allowed us to deriveaccurate light curves and, in turn, mean magnitudes and colors for asample of 53 RR Lyrae stars. To overcome the thorny problem ofdifferential reddening affecting this cluster, we derived new empiricalrelations connecting the intrinsic B-V and V-I colors of fundamental(RRab) RR Lyrae stars to the luminosity amplitude, the metallicity, andthe pulsation period. The key features of these relations are thefollowing: (1) they rely on stellar parameters, which are not affectedby reddening; (2) they supply accurate estimates of intrinsic colorsacross the fundamental instability strip and cover a wide metallicityrange; (3) they were derived by neglecting the RR Lyrae stars that areaffected by amplitude modulation. Moreover, the zero point of the E(B-V)reddening scale was empirically checked using the large sample of RRLyrae stars in M3 from Corwin & Carney, a GGC affected by avanishing reddening. According to these relations we estimatedindividual reddenings for RR Lyrae stars in our sample and the mainresults we found are the following: (1) The mean cluster reddening basedon E(B-V) color excesses is =0.30+/-0.03. This estimate isslightly higher than the mean reddening evaluations available in theliterature or based on the dust infrared map by Schlegel, Finkbeiner,& Davis, i.e., =0.26+/-0.02. Note that the angularresolution of this map is ~6', whereas for current reddening map it is~1'. (2) The mean cluster reddening based on E(V-I) color excesses is=0.36+/-0.05. This estimate is only marginally inagreement with the mean cluster reddening obtained using the reddeningmap by von Braun & Mateo and derived by adopting cluster turnoffstars, i.e., =0.25+/-0.07. On the other hand, currentintrinsic spread among individual reddenings (~0.2 mag) agrees quitewell with the estimate provided by previous authors. It is noteworthythat previous mean cluster reddenings are in very good agreement withvalues obtained using the empirical relations for intrinsic RR Lyraecolors provided by Kovacs & Walker. (3) According to currentindividual E(B-V) and E(V-I) reddenings and theoretical predictions forhorizontal-branch stars, we found that the true distance modulus forthis cluster is 13.32+/-0.06 mag. This determination is somehowsupported by the comparison between predicted and empirical pulsationamplitudes. (4) The comparison between present luminosity amplitudes andestimates available in the literature discloses that approximately 30%of fundamental RR Lyrae stars are affected by amplitude modulation (theBlazhko effect). This finding confirms empirical evidence originallybrought out by Szeidl and by Smith. Based on observations collected atthe European Southern Observatory, La Silla, Chile.
| Bias Properties of Extragalactic Distance Indicators. XI. Methods to Correct for Observational Selection Bias for RR Lyrae Absolute Magnitudes from Trigonometric Parallaxes Expected from the Full-Sky Astrometric Mapping Explorer Satellite
A short history is given of the development of the correction forobservation selection bias inherent in the calibration of absolutemagnitudes using trigonometric parallaxes. The developments have beendue to Eddington, Jeffreys, Trumpler & Weaver, Wallerstein,Ljunggren & Oja, West, Lutz & Kelker, after whom the bias isnamed, Turon Lacarrieu & Crézé, Hanson, Smith, andmany others. As a tutorial to gain an intuitive understanding of severalcomplicated trigonometric bias problems, we study a toy bias model of aparallax catalog that incorporates assumed parallax measuring errors ofvarious severities. The two effects of bias errors on the derivedabsolute magnitudes are (1) the Lutz-Kelker correction itself, whichdepends on the relative parallax error δπ/π and the spatialdistribution, and (2) a Malmquist-like ``incompleteness'' correction ofopposite sign due to various apparent magnitude cutoffs as they areprogressively imposed on the catalog. We calculate the bias propertiesusing simulations involving 3×106 stars of fixedabsolute magnitude using Mv=+0.6 to imitate RR Lyraevariables in the mean. These stars are spread over a spherical volumebounded by a radius 50,000 pc with different spatial densitydistributions. The bias is demonstrated by first using a fixed rmsparallax uncertainty per star of 50 μas and then using a variable rmsaccuracy that ranges from 50 μas at apparent magnitude V=9 to 500μas at V=15 according to the specifications for the Full-SkyAstrometric Mapping Explorer (FAME) satellite to be launched in 2004.The effects of imposing magnitude limits and limits on the``observer's'' error, δπ/π, are displayed. We contrast themethod of calculating mean absolute magnitude directly from theparallaxes where bias corrections are mandatory, with an inverse methodusing maximum likelihood that is free of the Lutz-Kelker bias, althougha Malmquist bias is present. Simulations show the power of the inversemethod. Nevertheless, we recommend reduction of the data using bothmethods. Each must give the same answer if each is freed from systematicerror. Although the maximum likelihood method will, in theory, eliminatemany of the bias problems of the direct method, nevertheless the biascorrections required by the direct method can be determined empiricallyvia Spaenhauer diagrams immediately from the data, as discussed in theearlier papers of this series. Any correlation of the absolute(trigonometric) magnitudes with the (trigonometric) distances is thebias. We discuss the level of accuracy that can be expected in acalibration of RR Lyrae absolute magnitudes from the FAME data over themetallicity range of [Fe/H] from 0 to -2, given the known frequency ofthe local RR Lyrae stars closer than 1.5 kpc. Of course, use will alsobe made of the entire FAME database for the RR Lyrae stars over thecomplete range of distances that can be used to empirically determinethe random and systematic errors from the FAME parallax catalog, usingcorrelations of derived absolute magnitude with distance and position inthe sky. These bias corrections are expected to be much more complicatedthan only a function of apparent magnitude because of variousrestrictions due to orbital constraints on the spacecraft.
| Aus der Sektion RR-Lyrae-Sterne.
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