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On the Spectroscopic Determination of Atmospheric Parameters and O/Fe Abundances of RR Lyrae Stars
In order to study how the conventional spectroscopic method based on theequivalent widths of the Fe I and Fe II lines effectively applies todetermining the atmospheric parameters (Teff, log g,vt, [Fe/H]) of RR Lyrae variables and how accurately theabundances can be established from such constructed model atmospheres,we analyzed 15 high-dispersion spectrograms of RR Lyr, DX Del, DH Peg,and VY Ser taken at several different phases by using the HDSspectrograph of the Subaru Telescope, and examined the consistency ofthe resulting phase-to-phase abundances. Taking oxygen as the targetelement along with Fe, we determined its non-LTE abundance from the O I6155-8 and 7771-5 triplets. It was found that consistent abundances wereobtained for O as well as Fe to a level of 0.1dex, irrespective ofthe pulsation phase, except for the special near-maximumhigh-temperature phase. This suggests that classical model atmospheresare reliably applicable to abundance determinations of RR Lyrae stars inmost cases. While the oxygen abundances derived from O I 7771-5 wellcorrelate with those from O I 6155-8, the former tends to besystematically larger by 0.1-0.2dex than the latter, which may beinterpreted as being due to the depth-dependence of the microturbulenceincreasing with height; i.e., the vt value derived fromdeep-forming Fe lines of weak/medium-strength may not be simply appliedto higher forming strong lines, such as O I 7771-5.
| 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.
| The GEOS RR Lyr Survey
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| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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| 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].
| 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.
| 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.
| Analysis of Select RR Lyrae Stars in Serpens from uvby beta Photometry
A uvby beta photoelectric photometry analysis of several RRstars in theliterature was carried out. From it, the physical parameters logT[eff]and logg were determined as well as the metallicity. From the latterquantity, an M[v] determination was carried out and a distance for eachstar was estimated. New frequencies are proposed for two stars.
| 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.
| Empirical calibration of the near-infrared CaII triplet - IV. The stellar population synthesis models
We present a new evolutionary stellar population synthesis model, whichpredicts spectral energy distributions for single-age single-metallicitystellar populations (SSPs) at resolution 1.5 Å (FWHM) in thespectral region of the near-infrared CaII triplet feature. The mainingredient of the model is a new extensive empirical stellar spectrallibrary that has been recently presented by Cenarro et al., which iscomposed of more than 600 stars with an unprecedented coverage of thestellar atmospheric parameters.Two main products of interest for stellar population analysis arepresented. The first is a spectral library for SSPs with metallicities-1.7 < [Fe/H] < +0.2, a large range of ages (0.1-18 Gyr) andinitial mass function (IMF) types. They are well suited to modellinggalaxy data, since the SSP spectra, with flux-calibrated responsecurves, can be smoothed to the resolution of the observational data,taking into account the internal velocity dispersion of the galaxy,allowing the user to analyse the observed spectrum in its own system. Wealso produce integrated absorption-line indices (namely CaT*, CaT andPaT) for the same SSPs in the form of equivalent widths.We find the following behaviour for the CaII triplet feature in old-agedSSPs: (i) the strength of the CaT* index does not change much with timefor all metallicities for ages larger than ~3 Gyr; (ii) this index showsa strong dependence on metallicity for values below [M/H]~-0.5 and (iii)for larger metallicities this feature does not show a significantdependence either on age or on the metallicity, being more sensitive tochanges in the slope of power-like IMF shapes.The SSP spectra have been calibrated with measurements for globularclusters by Armandroff & Zinn, which are well reproduced, probingthe validity of using the integrated CaII triplet feature fordetermining the metallicities of these systems. Fitting the models totwo early-type galaxies of different luminosities (NGC 4478 and 4365),we find that the CaII triplet measurements cannot be fitted unless avery dwarf-dominated IMF is imposed, or if the Ca abundance is evenlower than the Fe abundance. More details can be found in work byCenarro et al.
| Zur qualitat der visuellen Beobachtung kurzperiodisch Veranderlicher.
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| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
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| Empirical calibration of the near-infrared Ca II triplet - III. Fitting functions
Using a near-infrared stellar library of 706 stars with a wide coverageof atmospheric parameters, we study the behaviour of the CaII tripletstrength in terms of effective temperature, surface gravity andmetallicity. Empirical fitting functions for recently definedline-strength indices, namely CaT*, CaT and PaT, are provided. Thesefunctions can be easily implemented into stellar population models toprovide accurate predictions for integrated CaII strengths. We alsopresent a thorough study of the various error sources and their relationto the residuals of the derived fitting functions. Finally, the derivedfunctional forms and the behaviour of the predicted CaII are comparedwith those of previous works in the field.
| 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.
| 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.
| 7 BAV-Programmsterne.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
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| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| 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.
| 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.
| 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.
| A Test for Large-Scale Systematic Errors in Maps of Galactic Reddening
Accurate maps of Galactic reddening are important for a number ofapplications, such as mapping the peculiar velocity field in the nearbyuniverse. Of particular concern are systematic errors which vary slowlyas a function of position on the sky, as these would induce spuriousbulk flow. We have compared the reddenings of Burstein & Heiles (BH)and those of Schlegel, Finkbeiner, & Davis (SFD) to independentestimates of the reddening, for Galactic latitudes |b|>10^deg. Ourprimary source of Galactic reddening estimates comes from comparing thedifference between the observed B-V colors of early-type galaxies, andthe predicted B-V color determined from the B-V-Mg_2 relation. We havefitted a dipole to the residuals in order to look for large-scalesystematic deviations. There is marginal evidence for a dipolar residualin the comparison between the SFD maps and the observed early-typegalaxy reddenings. If this is due to an error in the SFD maps, then itcan be corrected with a small (13%) multiplicative dipole term. Weargue, however, that this difference is more likely to be due to a small(0.01 mag) systematic error in the measured B-V colors of the early-typegalaxies. This interpretation is supported by a smaller, independentdata set (globular cluster and RR Lyrae stars), which yields a resultinconsistent with the early-type galaxy residual dipole. BH reddeningsare found to have no significant systematic residuals, apart from theknown problem in the region 230^deg
| Modelling RR Lyrae pulsation: mission (im)possible?
In order to make an in-depth comparison between theory and observations,we analyse the light and velocity curves of various hydrodynamicalmodels simulating RRab stars. The observations are represented byempirical formulae, derived in this and our earlier papers. It is shownthat the overwhelming majority of the models tested do not follow theempirical relations regarding the shape of the light curves and thephysical parameters. In almost all cases the luminosities predicted fromthe model light curves are significantly lower than the correspondingmodel values. The overall discrepancy of the models is an importantindication of the limitation of the applicability of the presenttheoretical light and velocity curves in the determination of thephysical parameters of these stars. In transforming the theoretical datato the observed light curves in V colour and in computing the observedradial velocities, it is shown that both bolometric correction andtracing the line-forming regions have considerable effects on theevaluation of the observed quantities. In an effort to resolve thediscrepancy between theory and observations, it is suggested that aproper evaluation of the bolometric correction and radial velocity basedon complete dynamical atmosphere models may be a useful step in thisdirection.
| The slope of the RR Lyrae Mv-(Fe/H) relation
We review the available observational data to show that the slope of theRR Lyrae Mv-(Fe/H) relation is 0.18 +/- 0.03. The recent claim by Feastthat, because of biases, the true slope is much steeper is notjustified.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Csillagkép: | Kígyó |
| Rektaszcenzió: | 15h31m01.92s |
| Deklináció: | +01°41'01.7" |
| Vizuális fényesség: | 10.069 |
| RA sajátmozgás: | -104.8 |
| Dec sajátmozgás: | -9.8 |
| B-T magnitude: | 10.529 |
| V-T magnitude: | 10.107 |
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