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Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| RR Lyrae Atmospherics: Wrinkles Old and New. A Preview
I report some results of an echelle spectroscopic survey of RR Lyraestars begun in 2006 that I presented in my Henry Norris Lecture of 2010January 4. Topics include (1) atmospheric velocity gradients, (2)phase-dependent envelope turbulence as it relates to Peterson'sdiscoveries of axial rotation on the horizontal branch and to Stothers'explanation of the Blazhko effect, (3) the three apparitions of hydrogenemission during a pulsation cycle, (4) the occurrence of He I lines inemission and absorption, (5) detection of He II emission and metallicline doubling in Blazhko stars, and finally (6) speculation about whathelium observations of RR Lyrae stars in omega Centauri might tell usabout the putative helium populations and the horizontal branch of thatstrange globular cluster.This paper preserves the substance and style of remarks that accompaniedthe author's PowerPoint presentation of the 2009 Henry Norris Russelllecture.
| Recent Maxima of 64 Short Period Pulsating Stars
This paper contains times of maxima for 64 short period pulsating stars(primarily RR Lyrae and d Scuti stars). This represents a portion of theCCD observations received by the AAVSO Short Period Pulsator (SPP)section through December 2009.
| BAV-Results of Observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Study of globular cluster M53: new variables, distance, metallicity
Aims: We study the variable star content of the globular clusterM53 to compute the physical parameters of theconstituting stars and the distance of the cluster. Methods:Covering two adjacent seasons in 2007 and 2008, new photometric data aregathered for 3048 objects in the field of M53. Byusing the OIS (optimal image subtraction) method and subsequently TFA(trend filtering algorithm), we search for variables in the full sampleby using discrete Fourier transformation and box-fitting least squaresmethods. We select variables based on the statistics related to thesemethods combined with visual inspection. Results: We identified12 new variables (2 RR Lyrae stars, 7 short periodic stars - 3 of themare SX Phe stars - and 3 long-period variables). No eclipsing binarieswere found in the present sample. Except for the 3 (hitherto unknown)Blazhko RR Lyrae (two RRab and an RRc) stars, no multiperiodic variableswere found. We showed that after proper period shift, the PLC(period-luminosity-color) relation for the first overtone RR Lyraesample tightly follows the one spanned by the fundamental stars.Furthermore, the slope is in agreement with that derived from otherclusters. Based on the earlier Baade-Wesselink calibration of the PLCrelations, the derived reddening-free distance modulus ofM53 is 16.31±0.04 mag, corresponding to adistance modulus of 18.5 mag for the Large Magellanic Cloud. From theFourier parameters of the RRab stars we obtained an average ironabundance of -1.58± 0.03 (error of the mean). This is ~0.5 dexhigher than the overall abundance of the giants as given in theliterature and derived in this paper from the three-color photometry ofgiants. We suspect that the source of this discrepancy (observable alsoin other, low-metallicity clusters) is the lack of a sufficient numberof low-metallicity objects in the calibrating sample of the Fouriermethod.Table 1 is only available in electronic form at http://www.aanda.orgPhotometric data are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/507/803
| The RR Lyrae Period-Luminosity-(Pseudo)Color and Period-Color-(Pseudo)Color Relations in the Strömgren Photometric System: Theoretical Calibration
We present a theoretical calibration of the RR Lyraeperiod-luminosity-color and period-color-color relations in themultiband uvby Strömgren photometric system. Our theoretical workis based on calculations of synthetic horizontal branches (HBs) for fourdifferent metallicities, fully taking into account evolutionary effectsfor a wide range in metallicities and HB morphologies. While our resultsshow that ``pure'' period-luminosity and period-color relations do notexist in the Strömgren system, which is due to the large scatterthat is brought about by evolutionary effects when the uvby bandpassesare used, they also reveal that such scatter can be almost completelytaken into account by incorporating Strömgren pseudocolor[C0?(u-v)0-(v-b)0] terms intothose equations, thus leading to tight period-luminosity-pseudocolor(PLpsC) and period-color-pseudocolor (PCpsC) relations. We provide thelatter in the form of analytical fits, so that they can be applied withhigh precision even in the case of field stars. In view of the verysmall sensitivity of C0 to interstellar reddening, our PLpsCand PCpsC relations should be especially useful for the derivation ofhigh-precision distance and reddening values. In this sense, we carryout a first application of our relations to field RR Lyrae stars,finding evidence that the stars RR Lyr, SU Dra, and SS Leo, but not SVHya, are somewhat overluminous (by amounts ranging from ~=0.05 to 0.20mag in y, and thus V) with respect to the average for other RR Lyraestars of similar metallicity.
| 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.
| Korrekturen zu Vorhersagen im BAV Circular 2008.
Not Available
| The GEOS RR Lyr Survey
Not Available
| The GEOS RR Lyr Survey
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| Analysis of RR Lyrae Stars in the Northern Sky Variability Survey
We use data from the Northern Sky Variability Survey (NSVS), obtainedfrom the first-generation Robotic Optical Transient Search Experiment(ROTSE-I), to identify and study RR Lyrae variable stars in the solarneighborhood. We initially identified 1197 RRab (RR0) candidate starsbrighter than the ROTSE median magnitude V=14. Periods, amplitudes, andmean V magnitudes are determined for a subset of 1188 RRab stars withwell-defined light curves. Metallicities are determined for 589 stars bythe Fourier parameter method and by the relationship between period,amplitude, and [Fe/H]. We comment on the difficulties of clearlyclassifying RRc (RR1) variables in the NSVS data set. Distances to theRRab stars are calculated using an adopted luminosity-metallicityrelation with corrections for interstellar extinction. The 589 RRabstars in our final sample are used to study the properties of the RRabpopulation within 5 kpc of the Sun. The Bailey diagram of period versusamplitude shows that the largest component of this sample belongs toOosterhoff type I. Metal-rich ([Fe/H]>-1) RRab stars appear to beassociated with the Galactic disk. Our metal-rich RRab sample mayinclude a thin-disk, as well as a thick-disk population, although theuncertainties are too large to establish this. There is some evidenceamong the metal-rich RRab stars for a decline in scale height withincreasing [Fe/H], as was found by Layden. The distribution of RRabstars with -1<[Fe/H]<-1.25 indicates that within this metallicityrange the RRab stars are a mixture of stars belonging to halo and diskpopulations.
| 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.
| 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.
| Iron abundances derived from RR Lyrae light curves and low-dispersion spectroscopy
With the aid of the All Sky Automated Survey (ASAS) database on theGalactic field, we compare the iron abundances of fundamental mode RRLyrae stars derived from the Fourier parameters with those obtained fromlow-dispersion spectroscopy. We show from a set of 79 stars, distinctfrom the original calibrating sample of the Fourier method and selectedwithout quality control, that almost all discrepant estimates are theresults of some defects or peculiarities either in the photometry or inthe spectroscopy. Omitting objects deviating by more than 0.4 dex, theremaining subsample of 64 stars yields Fourier abundances that fit thespectroscopic ones with σ=0.20 dex. Other, more stringentselection criteria and different Fourier decompositions lead to smallersubsamples and concomitant better agreement, down to σ=0.16 dex.Except perhaps for two variables among the 163 stars, comprised of theASAS variables and those of the original calibrating set of the Fouriermethod, all discrepant values can be accounted for by observationalnoise and insufficient data coverage. We suggest that the agreement canbe further improved when new, more accurate spectroscopic data becomeavailable for a test with the best photometric data. As a by-product ofthis analysis, we also compute revised periods and select Blazhkovariables.
| Predicted and Empirical Radii of RR Lyrae Stars
We present new theoretical period-radius-metallicity relations for RRLyrae stars. Current predictions are based on a large set of nonlinear,convective models that cover a broad range of chemical abundances andinput parameters. We also provide new and homogeneous estimates ofangular diameters for a sample of field RR Lyrae stars using a recentcalibration of the Barnes-Evans surface brightness relation. Predictedand empirical radii are, within the errors, in reasonable agreement, butin the short-period range the latter present a larger scatter. As aworking hypothesis we suggest that this discrepancy might be due to theoccurrence either of nonlinear features such as bumps or a steep risingbranch. A new distance determination for RR Lyr itself is in very goodagreement with the Hubble Space Telescope trigonometric parallax andwith the pulsation parallax.
| 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 GEOS RR Lyr Survey
Not Available
| Photoelectric Maxima of Selected Pulsating Stars
Not Available
| 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.
| The Millennium Galaxy Catalogue: 16 <=BMGC < 24 galaxy counts and the calibration of the local galaxy luminosity function
The Millennium Galaxy Catalogue (MGC) is a 37.5 deg2,medium-deep, B-band imaging survey along the celestial equator, takenwith the Wide Field Camera on the Isaac Newton Telescope. The surveyregion is contained within the regions of both the Two Degree FieldGalaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey EarlyData Release (SDSS-EDR). The survey has a uniform isophotal detectionlimit of 26 mag arcsec-2 and it provides a robust,well-defined catalogue of stars and galaxies in the range 16<=BMGC < 24 mag.Here we describe the survey strategy, the photometric and astrometriccalibration, source detection and analysis, and present the galaxynumber counts that connect the bright and faint galaxy populationswithin a single survey. We argue that these counts represent the stateof the art and use them to constrain the normalizations (φ*) of anumber of recent estimates of the local galaxy luminosity function. Wefind that the 2dFGRS, SDSS Commissioning Data (CD), ESO Slice Project,Century Survey, Durham/UKST, Mt Stromlo/APM, SSRS2 and NOG luminosityfunctions require a revision of their published φ* values by factorsof 1.05 +/- 0.05, 0.76 +/- 0.10, 1.02 +/- 0.22, 1.02 +/- 0.16, 1.16 +/-0.28, 1.75 +/- 0.37, 1.40 +/- 0.26 and 1.01 +/- 0.39, respectively.After renormalizing the galaxy luminosity functions we find a mean localbJ luminosity density of .1
| 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.
| 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.
| BAV-Beobachtungen an Programmsternen des Typs RR-Lyrae von 1951 bis 2001.
Not Available
| RR Lyrae pulsational temperature scales: on the consistency between different empirical relations
In this paper, by assuming the equilibrium temperatures of RRab Lyraevariables defined by Carney, Storm & Jones as correct we show thattemperatures derived from (B-V) colour (mean colour over the pulsationalcycle calculated on the magnitude scale) transformations by Bessel,Castelli & Plez are consistent with the Carney et al. equilibriumtemperatures within a probable error ofδlogTe=+/-0.003. As a consequence, it is shown that thepulsational temperature scale temperature-period-blue amplitude[Teff=f(P,AB)] relation provided by De Santis, whostudied the (B-V) colour of about 70 stars of Lub's sample, is asuitable relation, being reddening- and metallicity-free, to calculateequilibrium temperatures for RRab variables. This relation isindependent of variable mass and luminosity within a large range ofperiod-shift from the mean period-amplitude relation valid for Lub'ssample of variables. On the contrary, it is also shown that atemperature-amplitude-metallicity relation is strictly dependent on theperiod-amplitude relation of the sample used for calibrating it: weprove that this means it is dependent on both the mass and luminosityvariations of variables.
| 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.
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Observation and Astrometry data
| Constellation: | Löwe |
| Right ascension: | 11h33m54.49s |
| Declination: | -00°02'00.0" |
| Apparent magnitude: | 10.914 |
| Proper motion RA: | -25.2 |
| Proper motion Dec: | -26.1 |
| B-T magnitude: | 11.277 |
| V-T magnitude: | 10.944 |
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