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Публикации по объекту
Mid-infrared Period-luminosity Relations of RR Lyrae Stars Derived from the WISE Preliminary Data Release
Interstellar dust presents a significant challenge to extendingparallax-determined distances of optically observed pulsationalvariables to larger volumes. Distance ladder work at mid-infraredwavebands, where dust effects are negligible and metallicitycorrelations are minimized, has been largely focused on few-epochCepheid studies. Here we present the first determination of mid-infraredperiod-luminosity (PL) relations of RR Lyrae stars from phase-resolvedimaging using the preliminary data release of the Wide-field InfraredSurvey Explorer (WISE). We present a novel statistical framework topredict posterior distances of 76 well observed RR Lyrae that uses theoptically constructed prior distance moduli while simultaneouslyimposing a power-law PL relation to WISE-determined mean magnitudes. Wefind that the absolute magnitude in the bluest WISE filter is MW1 = (- 0.421 ± 0.014) - (1.681 ±0.147)log10(P/0.50118 day), with no evidence for acorrelation with metallicity. Combining the results from the threebluest WISE filters, we find that a typical star in our sample has adistance measurement uncertainty of 0.97% (statistical) plus 1.17%(systematic). We do not fundamentalize the periods of RRc stars toimprove their fit to the relations. Taking the Hipparcos-derived meanV-band magnitudes, we use the distance posteriors to determine a newoptical metallicity-luminosity relation. The results of this analysiswill soon be tested by Hubble Space Telescope parallax measurements and,eventually, with the GAIA astrometric mission.
| New high-sensitivity, milliarcsecond resolution results from routine observations of lunar occultations at the ESO VLT
Context. Lunar occultations (LO) are a very efficient and powerfultechnique that achieves the best combination of high angular resolutionand sensitivity possible today at near-infrared wavelengths. Given thatthe events are fixed in time, that the sources are occulted randomly,and that the telescope use is minimal, the technique is very well suitedfor service mode observations. Aims: We have established aprogram of routine LO observations at the VLT observatory, especiallydesigned to take advantage of short breaks available in-between otherprograms. We have used the ISAAC instrument in burst mode, capable ofproducing continuous read-outs at millisecond rates on a suitablesubwindow. Given the random nature of the source selection, our aim hasbeen primarily the investigation of a large number of stellar sources atthe highest angular resolution in order to detect new binaries.Serendipitous results such as resolved sources and detection ofcircumstellar components were also anticipated. Methods: We haverecorded the signal from background stars for a few seconds, around thepredicted time of occultation by the Moon's dark limb. At millisecondtime resolution, a characteristic diffraction pattern can be observed.Patterns for two or more sources superimpose linearly, and this propertyis used for the detection of binary stars. The detailed analysis of thediffraction fringes can be used to measure specific properties such asthe stellar angular size and the presence of extended light sources suchas a circumstellar shell. Results: We present a list of 191 starsfor which LO data could be recorded and analyzed. Results include thedetection of 16 binary and 2 triple stars, all but one of which werepreviously unknown. The projected angular separations are as small as 4milliarcsec and magnitude differences as high as ? K = 5.8 mag.Additionally we derive accurate angular diameters for 2 stars andresolve circumstellar emission around another one, also all for thefirst time. We have established upper limits on the angular size of 177stars, mostly in the 1 to 5 mas range, and we plan to include them in afuture list of sources well suited for the calibration ofinterferometers. Conclusions: We confirm the performance of thetechnique already established in our previous work. LO at an 8 m-classtelescope can achieve an angular resolution close to 0farcs001 with asensitivity K ? 12 mag.Based on observations made with ESO telescopes at Paranal Observatory.
| The luminosities and distance scales of type II Cepheid and RR Lyrae variables
Infrared and optical absolute magnitudes are derived for the type IICepheids κ Pav and VY Pyx using revised Hipparcos parallaxes andfor κ Pav, V553 Cen and SW Tau from pulsational parallaxes.Revised Hipparcos and HST parallaxes for RR Lyrae agree satisfactorilyand are combined in deriving absolute magnitudes. Phase-corrected J, Hand Ks mags are given for 142 Hipparcos RR Lyraes based onTwo-Micron All-Sky Survey observations. Pulsation and trigonometricalparallaxes for classical Cepheids are compared to establish the bestvalue for the projection factor (p) used in pulsational analyses.The MV of RR Lyrae itself is 0.16 +/- 0.12 mag brighter thanpredicted from an MV-[Fe/H] relation based on RR Lyrae starsin the Large Magellanic Cloud (LMC) at a modulus of 18.39 +/- 0.05 asfound from classical Cepheids. This is consistent with the prediction ofCatelan & Cortés that it is overluminous for its metallicity.The results for the metal- and carbon-rich Galactic disc stars, V553 Cenand SW Tau, each with small internal errors (+/-0.08 mag) have a meandeviation of only 0.02 mag from the period-luminosity (PL) relationestablished by Matsunaga et al. for type II Cepheids in globularclusters and with a zero-point based on the same LMC-scale. Comparingdirectly the luminosities of these two stars with published data on typeII Cepheids in the LMC and in the Galactic bulge leads to an LMC modulusof 18.37 +/- 0.09 and a distance to the Galactic Centre of R0= 7.64 +/- 0.21kpc. The data for VY Pyx agree with these results withinthe uncertainties set by its parallax. Evidence is presented thatκ Pav may have a close companion and possible implications of thisare discussed. If the pulsational parallax of this star is incorporatedin the analyses, the distance scales just discussed will be increased by~0.15 +/- 0.15 mag. V553 Cen and SW Tau show that at optical wavelengthsPL relations are wider for field stars than for those in globularclusters. This is probably due to a narrower range of masses in thelatter case.
| Pulsational and evolutionary analysis of the double-mode RR Lyrae star BSCom
We derive the basic physical parameters of the field double-mode RRLyrae star BSCom from its observed periods and the requirement ofconsistency between the pulsational and evolutionary constraints. Byusing the current solar-scaled horizontal branch evolutionary models ofPietrinferni et al. and our linear non-adiabatic purely radiativepulsational models, we get M/Msolar = 0.698 +/- 0.004,log(L/Lsolar) = 1.712 +/- 0.005, Teff = 6840 +/-14K, [Fe/H] = -1.67 +/- 0.01, where the errors are standard deviationsassuming uniform age distribution along the full range of uncertainty inage. The last two parameters are in a good agreement with the onesderived from the observed BVIC colours and the updated ATLAS9stellar atmosphere models. We get Teff = 6842 +/- 10K, [Fe/H]= -1.58 +/- 0.11, where the errors are purely statistical ones. It isremarkable that the derived parameters are nearly independent of stellarage at early evolutionary stages. Later stages, corresponding to theevolution towards the asymptotic giant branch, are most probablyexcluded because the required high temperatures are less likely tosatisfy the constraints posed by the colours. We also show that ourconclusions are only weakly sensitive to non-linear period shiftspredicted by current hydrodynamical models.
| The Extinction Toward the Galactic Bulge from RR Lyrae Stars
We present mean reddenings toward 3525 RR0 Lyrae stars from the Galacticbulge fields of the MACHO Survey. These reddenings are determined usingthe color at minimum V-band light of the RR0 Lyrae stars themselves andare found to be in general agreement with extinction estimates at thesame location obtained from other methods. Using 3256 stars located inthe Galactic Bulge, we derive the selective extinction coefficientRV,VR = AV/E(V - R) = 4.3 ± 0.2. This valueis what is expected for a standard extinction law with RV,BV= 3.1 ± 0.3.
| A list of minima and maxima timings
The list contains minima of eclipsing and maxima of pulsatings stars, itcontinues the list published in OEJV 0048.
| Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for MILES, a new spectral stellarlibrary covering the range λλ 3525-7500Å at2.3Å (FWHM) spectral resolution. The library consists of 985 starsspanning a large range in atmospheric parameters, from super-metal-rich,cool stars to hot, metal-poor stars. The spectral resolution, spectraltype coverage and number of stars represent a substantial improvementover previous libraries used in population synthesis models. Theatmospheric parameters that we present here are the result of aprevious, extensive compilation from the literature. In order toconstruct a homogeneous data set of atmospheric parameters we have takenthe sample of stars of Soubiran, Katz & Cayrel, which has very welldetermined fundamental parameters, as the standard reference system forour field stars, and have calibrated and bootstrapped the data fromother papers against it. The atmospheric parameters for our clusterstars have also been revised and updated according to recent metallicityscales, colour-temperature relations and improved set of isochrones.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| [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.
| 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.
| Metallicity Dependence of the Blazhko Effect
The microlensing surveys, such as OGLE or MACHO, have led to thediscovery of thousands of RRLyr stars in the Galactic bulge and in theMagellanic Clouds, allowing for detailed investigation of these stars,especially the still mysterious Blazhko phenomenon. Higher incidencerate of Blazhko (BL) variables in the more metal-rich Galactic bulgethan in the LMC, suggests that occurrence of Blazhko effect correlateswith metallicity. To investigate this problem, we calibrate thephotometric method of determining the metallicity of RRab stars in theI-band and apply it to the OGLE Galactic bulge and LMC data. In bothsystems, metallicities of non Blazhko and Blazhko variables are close toeach other. The LMC Blazhko pulsators prefer slightly lowermetallicities. The different metallicities of the Galactic bulge and theLMC, cannot explain the observed incidence rates.As a by-product of our metallicity estimates, we investigate theluminosity-metallicity relation, finding a steep dependence of theluminosity on [Fe/H].
| 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.
| 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.
| 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.
| 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.
| Empirical relations for cluster RR Lyrae stars revisited
Our former study on the empirical relations between the Fourierparameters of the light curves of the fundamental mode RR Lyrae starsand their basic stellar parameters has been extended to considerablylarger data sets. The most significant contribution to the absolutemagnitude MV comes from the period P and from the firstFourier amplitude A1, but there are statistically significantcontributions also from additional higher order components, mostimportantly from A3 and in a lesser degree from the Fourierphase varphi51. When different colors are combined inreddening-free quantities, we obtain basically period-luminosity-colorrelations. Due to the log Teff(B-V,log g,[Fe/H]) relationfrom stellar atmosphere models, we would expect some dependence also onvarphi 31. Unfortunately, the data are still not extensiveand accurate enough to decipher clearly the small effect of this Fourierphase. However, with the aid of more accurate multicolor data on fieldvariables, we show that this Fourier phase should be present either inV-I or in B-V or in both. From the standard deviations of the variousregressions, an upper limit can be obtained on the overall inhomogeneityof the reddening in the individual clusters. This yields sigmaE(B-V)<~ 0.012 mag, which also implies an average minimumobservational error of sigmaV >~ 0.018 mag.
| Absolute Magnitudes and Kinematic Parameters of the Subsystem of RR Lyrae Variables
The statistical parallax technique is applied to a sample of 262 RRabLyrae variables with published photoelectric photometry, metallicities,and radial velocities and with measured absolute proper motions.Hipparcos, PPM, NPM, and the Four-Million Star Catalog (Volchkov et al.1992) were used as the sources of proper motions; the proper motionsfrom the last three catalogs were reduced to the Hipparcos system. Wedetermine parameters of the velocity distribution for halo [(U_0, V_0,W_0) = (-9 +/- 12, -214 +/- 10, -16 +/- 7) km/s and (sigma_U, sigma_V,sigma_W) = (164 +/- 11, 105 +/- 7, 95 +/- 7) km/s] and thick-disk [(U_0,V_0, W_0) = (-16 +/- 8, -41 +/- 7, -18 +/- 5) km/s and (sigma_U,sigma_V, sigma_W) = (53 +/- 9, 42 +/- 8, 26 +/- 5) km/s] RR Lyrae, aswell as the intensity-averaged absolute magnitude for RR Lyrae of thesepopulations: = 0.77 +/- 0.10 and = +1.11 +/-0.28 for the halo and thick-disk objects, respectively. The metallicitydependence of the absolute magnitude of RR Lyrae is analyzed(=(0.76 +/- 0.12) + (0.26 +/- 0.26) x ([Fe/H] + 1.6) = 1.17 +0.26 x [Fe/H]). Our results are in satisfactory agreement with the_(RR)-[Fe/H] relation from Carney et al. (1992)(_(RR) = 1.01 + 0.15 x [Fe/H]) obtained by Baade-Wesselink'smethod. They provide evidence for a short distance scale: the LMCdistance modulus and the distance to the Galactic center are 18.22 +/-0.11 and 7.4 +/-±0.5 kpc, respectively. The zero point ofthe distance scale and the kinematic parameters of the RR Lyraepopulations are shown to be virtually independent of the source ofabsolute proper motions used and of whether they are reduced to theHipparcos system or not.
| 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.
| The absolute magnitudes of RR Lyraes from HIPPARCOS parallaxes and proper motions
We have used HIPPARCOS proper motions and the method of StatisticalParallax to estimate the absolute magnitude of RR Lyrae stars. Inaddition we used the HIPPARCOS parallax of RR Lyrae itself to determineit's absolute magnitude. These two results are in excellent agreementwith each other and give a zero-point for the RR Lyrae M_v,[Fe/H]relation of 0.77+/-0.15 at [Fe/H]=-1.53. This zero-point is in goodagreement with that obtained recently by several groups usingBaade-Wesselink methods which, averaged over the results from thedifferent groups, gives M_v = 0.73+/-0.14 at [Fe/H]=-1.53. Taking theHIPPARCOS based zero-point and a value of 0.18+/-0.03 for the slope ofthe M_v,[Fe/H] relation from the literature we find firstly, thedistance modulus of the LMC is 18.26+/-0.15 and secondly, the mean ageof the Globular Clusters is 17.4+/-3.0 GYrs. These values are comparedwith recent estimates based on other "standard candles" that have alsobeen calibrated with HIPPARCOS data. It is clear that, in addition toastrophysical problems, there are also problems in the application ofHIPPARCOS data that are not yet fully understood. Table 1, whichcontains the basic data for the RR Lyraes, is available only at CDS. Itmay be retrieved via anonymous FTP at cdsarc.u-strasbg.fr (130.79.128.5)or via the Web at http://cdsweb.u-strasbg.fr/Abstract.html
| Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars
The kinematics of 122 red giant and 124 RR Lyrae stars in the solarneighborhood are studied using accurate measurements of their propermotions obtained by the Hipparcos astrometry satellite, combined withtheir published photometric distances, metal abundances, and radialvelocities. A majority of these sample stars have metal abundances of(Fe/H) = -1 or less and thus represent the old stellar populations inthe Galaxy. The halo component, with (Fe/H) = -1.6 or less, ischaracterized by a lack of systemic rotation and a radially elongatedvelocity ellipsoid. About 16 percent of such metal-poor stars have loworbital eccentricities, and we see no evidence of a correlation between(Fe/H) and e. Based on the model for the e-distribution of orbits, weshow that this fraction of low-e stars for (Fe/H) = -1.6 or less isexplained by the halo component alone, without introducing the extradisk component claimed by recent workers. This is also supported by theabsence of a significant change in the e-distribution with height fromthe Galactic plane. In the intermediate-metallicity range, we find thatstars with disklike kinematics have only modest effects on thedistributions of rotational velocities and e for the sample at absolutevalue of z less than 1 kpc. This disk component appears to constituteonly 10 percent for (Fe/H) between -1.6 and -1 and 20 percent for (Fe/H)between -1.4 and -1.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Computation of the distance moduli of RR Lyrae stars from their light and colour curves.
We use B and V data of globular cluster variables to derive a formulafor the distance moduli of RRab stars. The method employs the Fourierdecomposition of the V light curve and the average B-V colour index. Byusing our former result for the V_0_ absolute magnitude, we also obtainan expression for the dereddened colour index. With the aid of the newformulae, the relative distance moduli can be estimated within an errorof <0.03mag. Although we also make an absolute calibration, it iscautioned that this may be more affected by possible systematic errorsoriginating mostly from the Baade-Wesselink magnitudes. On the basis ofthe scatter of the individual distance moduli computed with and withoutreddening correction, it is shown that inhomogeneous reddening plays arole in several clusters. By using our formulae we derive newexpressions for the I_c_ and K absolute magnitudes on a sample of starswhich contains mostly field stars with accurate photometry. As aby-product of this derivation we also give optimum estimations for theselective absorption coefficient R_V_. We show that the K absolutemagnitude contains important contribution also from the Fourierparameters, besides the well known dependence on the period. The I_c_absolute magnitude is superbly correlated with the Fourier parameters,which implies that this colour is a very good candidate for the accurateestimation of the absolute magnitude.
| Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering
Not Available
| The Absolute Magnitude and Kinematics of RR Lyrae Stars Via Statistical Parallax
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2110L&db_key=AST
| Determination of [Fe/H] from the light curves of RR Lyrae stars.
We present an accurate and robust method for the calculation of [Fe/H]from the light curves of RRab stars. The method introduces aconsiderable improvement relative to our previously published formulae.First of all, it uses an improved and extended data base for the lightcurves and more accurate, very recent iron abundances. Secondly, the newdata base makes it possible to show that the basic relation between[Fe/H] and the Fourier parameters is linear and contains only the periodand one of the Fourier phases, most importantly φ_31_. Last but notleast, we derive interrelations among the Fourier parameters which helpus to filter out peculiar stars where more caution is needed inaccepting the calculated abundance. The applicability of the method isdemonstrated on independent samples of globular cluster stars.Peculiarities encountered in Blazhko variables and in some other casesare also discussed.
| 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 Composition of HB Stars: RR Lyrae Variables
We used moderately high-resolution, high S/N spectra to study thechemical composition of 10 field ab-type RR Lyrae stars. A newtemperature scale was determined from literature Infrared Flux Methodmeasures of subdwarfs and the Kurucz (1992) model atmospheres, and usedto calibrate colors for both dwarfs and RR Lyraes. The applicability ofKurucz (1992) model atmospheres in the analysis of RR Lyraes at minimumlight was analyzed: we found that they are able to reproduce colors,excitation and ionization equilibria as well as the wings of Halpha. Wederived abundances for 21 species. The metal abundances of the programstars span the range -2.50<[Fe/H]<+0.17$. Lines of most elementsare found to form in LTE conditions. Fe lines satisfy very well theexcitation and ionization equilibria. RR Lyraes share the typicalabundance pattern of other stars of similar [Fe/H]: alpha-elements areoverabundant by about 0.4dex and Mn is underabundant by about 0.6dex instars with [Fe/H]<-1. Significant departures from LTE are found onlyfor a few species. We used our new [Fe/H] abundances, as well as valuesfrom Butler and coworkers (corrected to our system), and from highresolution spectroscopy of globular clusters giants, to obtain a newcalibration of the DeltaS index: [Fe/H]= -0.194(\pm 0.011)DeltaS-0.08(\pm 0.18) and to update the metallicity calibration of the Ca II Kline index: [Fe/H]= 0.65(\pm 0.17)W'(K) -3.49(\pm 0.39). Finally, ournew metallicity scale was used to revise the [Fe/H] dependence of theabsolute magnitude of RR Lyrae stars, Mv: Mv = 0.20(\pm 0.03)[Fe/H] +1.06(\pm 0.04).
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Стрелец |
| Прямое восхождение: | 19h32m20.78s |
| Склонение: | -23°51'12.8" |
| Видимая звёздная величина: | 10.817 |
| Собственное движение RA: | -5.1 |
| Собственное движение Dec: | -58.7 |
| B-T magnitude: | 10.942 |
| V-T magnitude: | 10.828 |
Каталоги и обозначения:
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