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The kinematic properties of BHB and RR Lyrae stars towards the Anticentre and the North Galactic Pole: the transition between the inner and the outer halo
We identify 51 blue horizontal branch (BHB) stars, 12 possible BHB starsand 58 RR Lyrae stars in Anticentre fields. Their selection does notdepend on their kinematics. Light curves and ephemerides are given forseven previously unknown RR Lyrae stars. All but four of the RR Lyraestars are of Oosterhoff type I.Our selection criteria for BHB stars give results that agree with thoseused by Smith et al. and Ruhland et al. We use five methods to determinedistances for the BHB stars and three methods for the RR Lyrae stars toget distances on a uniform scale. Absolute proper motions [largelyderived from the Second Guide Star Catalogue (GSCII) and Sloan DigitalSky Survey (Seventh Data Release) data bases] are given for these stars;radial velocities are given for 31 of the BHB stars and 37 of the RRLyrae stars.Combining these data for BHB and RR Lyrae stars with those previouslyfound in fields at the North Galactic Pole, we find that retrogradeorbits dominate for galactocentric distances greater than 12.5 kpc. Themajority of metal-poor stars in the solar neighbourhood are known to beconcentrated in a L? versus Lz angularmomentum plot. We show that the ratio of the number of outliers to thenumber in the main concentration increases with galactocentric distance.The location of these outliers with L? and Lzshows that the halo BHB and RR Lyrae stars have more retrograde orbitsand a more spherical distribution with increasing galactocentricdistance. Six RR Lyrae stars are identified in the H99 group ofoutliers; the small spread in their [Fe/H] suggests that they could havecome from a single globular cluster. Another group of outliers containstwo pairs of RR Lyrae stars; the stars in each pair have similarproperties.
| The Determination of Reddening from Intrinsic VR Colors of RR Lyrae Stars
New R-band observations of 21 local field RR Lyrae variable stars areused to explore the reliability of minimum light (V - R) colors asa tool for measuring interstellar reddening. For each star, R-bandintensity mean magnitudes and light amplitudes are presented.Corresponding V-band light curves from the literature are supplementedwith the new photometry, and (V - R) colors at minimum light aredetermined for a subset of these stars as well as for other stars in theliterature. Two different definitions of minimum light color areexamined, one which uses a Fourier decomposition to the V and R lightcurves to find (V - R) at minimum V-band light, (V - R)F min, and the other which uses the average colorbetween the phase interval 0.5-0.8, (V -R)phi(0.5-0.8) min. From 31 stars with awide range of metallicities and pulsation periods, the mean dereddenedRR Lyrae color at minimum light is (V - R) F min,0 = 0.28 ± 0.02 mag and (V -R)phi(0.5-0.8) min,0 = 0.27 ± 0.02mag. As was found by Guldenschuh et al. using (V - I) colors, anydependence of the star's minimum light color on metallicity or pulsationamplitude is too weak to be formally detected. We find that theintrinsic (V - R) of Galactic bulge RR Lyrae stars are similar tothose found by their local counterparts and hence that bulge RR0 Lyraestars do not have anomalous colors as compared to the local RR Lyraestars.
| BAV-Results of Observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Automated Variable Star Classification Using the Northern Sky Variability Survey
We have identified 4659 variable objects in the Northern Sky VariabilitySurvey. We have classified each of these objects into one of the fivevariable star classes: (1) Algol/β Lyr systems includingsemidetached, and detached eclipsing binaries, (2) W Ursae Majorisovercontact and ellipsoidal variables, (3) long-period variables such asCepheid and Mira-type objects, (4) RR Lyr pulsating variables, and (5)short-period variables including δ Scuti stars. All the candidateshave outside of eclipse magnitudes of ~10-13. The primary classificationtool is the use of Fourier coefficients combined with period informationand light-curve properties to make the initial classification. Briefmanual inspection was done on all light curves to remove nonperiodicvariables that happened to slip through the process and to quantify anyerrors in the classification pipeline. We list the coordinates, period,Two Micron All Sky Survey colors, total amplitude variation, and anyprevious classification of the object. 548 objects previously identifiedas Algols in our previous paper are not included here.
| 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.
| Korrekturen zu Vorhersagen im BAV Circular 2008.
Not Available
| Einfuhrung quadratischer Lichtwechselelemente.
Not Available
| Stellar evolution through the ages: period variations in galactic RRab stars as derived from the GEOS database and TAROT telescopes
Context: The theory of stellar evolution can be more closely tested ifwe have the opportunity to measure new quantities. Nowadays,observations of galactic RR Lyr stars are available on a time baselineexceeding 100 years. Therefore, we can exploit the possibility ofinvestigating period changes, continuing the pioneering work started byV. P. Tsesevich in 1969. Aims: We collected the available times ofmaximum brightness of the galactic RR Lyr stars in the GEOS RR Lyrdatabase. Moreover, we also started new observational projects,including surveys with automated telescopes, to characterise the O-Cdiagrams better. Methods: The database we built has proved to be a verypowerful tool for tracing the period variations through the ages. Weanalyzed 123 stars showing a clear O-C pattern (constant, parabolic orerratic) by means of different least-squares methods. Results: Clearevidence of period increases or decreases at constant rates has beenfound, suggesting evolutionary effects. The median values are β =+0.14 d Myr-1 for the 27 stars showing a period increase andβ = -0.20 d Myr-1 for the 21 stars showing a perioddecrease. The large number of RR Lyr stars showing a period decrease(i.e., blueward evolution) is a new and intriguing result. There is anexcess of RR Lyr stars showing large, positive β values. Moreover,the observed β values are slightly larger than those predicted bytheoretical models.Tables 3, 4, 5 and Figs. 2, 3 are only available in electronic form athttp://www.aanda.org
| The GEOS RR Lyr Survey
Not Available
| Bright Metal-poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields
We present a sample of 1777 bright (91.0) metal-poor([Fe/H]<-2.0) giants of 9%+/-2%, which is lower than previouslyreported. However, the frequency rises to similar (>20%) and highervalues with increasing distance from the Galactic plane. Although thenumbers of stars at low metallicity are falling rapidly at the lowestmetallicities, there is evidence that the fraction of carbon-enhancedmetal-poor stars is increasing rapidly as a function of decliningmetallicity. For ~60 objects, high-resolution data have already beenobtained; one of these, HE 1327-2326, is the new record holder for themost iron-deficient star known.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Proper identification of RR Lyrae stars brighter than 12.5 mag
RR Lyrae stars are of great importance for investigations of Galacticstructure. However, a complete compendium of all RR-Lyraes in the solarneighbourhood with accurate classifications and coordinates does notexist to this day. Here we present a catalogue of 561 local RR-Lyraestars (V_max ≤ 12.5 mag) according to the magnitudes given in theCombined General Catalogue of Variable Stars (GCVS) and 16 fainter ones.The Tycho2 catalogue contains ≃100 RR Lyr stars. However, manyobjects have inaccurate coordinates in the GCVS, the primary source ofvariable star information, so that a reliable cross-identification isdifficult. We identified RR Lyrae from both catalogues based on anintensive literature search. In dubious cases we carried out photometryof fields to identify the variable. Mennessier & Colome (2002,A&A, 390, 173) have published a paper with Tyc2-GCVSidentifications, but we found that many of their identifications arewrong.
| RR Lyrae stars: kinematics, orbits and z-distribution
RR Lyrae stars in the Milky Way are good tracers to study the kinematicbehaviour and spatial distribution of older stellar populations. Arecently established well documented sample of 217 RR Lyr stars withV<12.5 mag, for which accurate distances and radial velocities aswell as proper motions from the Hipparcos and Tycho-2 catalogues areavailable, has been used to reinvestigate these structural parameters.The kinematic parameters allowed to calculate the orbits of the stars.Nearly 1/3 of the stars of our sample have orbits staying near the MilkyWay plane. Of the 217 stars, 163 have halo-like orbits fulfilling one ofthe following criteria: Θ < 100 km s-1, orbiteccentricity >0.4, and normalized maximum orbital z-distance>0.45. Of these stars roughly half have retrograde orbits. Thez-distance probability distribution of this sample shows scale heightsof 1.3±0.1 kpc for the disk component and 4.6±0.3 kpc forthe halo component. With our orbit statistics method we found a(vertical) spatial distribution which, out to z=20 kpc, is similar tothat found with other methods. This distribution is also compatible withthe ones found for blue (HBA and sdB) halo stars. The circular velocityΘ, the orbit eccentricity, orbit z-extent and [Fe/H] are employedto look for possible correlations. If any, it is that the metal poorstars with [Fe/H] <1.0 have a wide symmetric distribution aboutΘ=0, thus for this subsample on average a motion independent ofdisk rotation. We conclude that the Milky Way possesses a halo componentof old and metal poor stars with a scale height of 4-5 kpc having randomorbits. The presence in our sample of a few metal poor stars (thus partof the halo population) with thin disk-like orbits is statistically notsurprising. The midplane density ratio of halo to disk stars is found tobe 0.16, a value very dependent on proper sample statistics.
| The GEOS RR Lyr Survey
Not Available
| 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.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
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| Ein Hoch auf die Hochs Helga und Liljana.
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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.
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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
| A New Analysis of RR Lyrae Kinematics in the Solar Neighborhood
Full space velocities are computed for a sample of 130 nearby RR Lyraevariables using both ground-based and Hipparcos proper motions. In manycases proper motions for the same star from multiple sources have beenaveraged to produce approximately a factor of 2 improvement in thetransverse space velocity errors. In most cases, this exceeds theaccuracy attained using Hipparcos proper motions alone. The velocityellipsoids computed for halo and thick-disk samples are in agreementwith those reported in previous studies. A distinct sample of thin-diskRR Lyrae variables has not been isolated, but there is kinematicevidence for some thin-disk contamination in our thick-disk samples.Using kinematic and spatial parameters, a sample of 21 stars with [Fe/H]< -1.0 and disklike kinematics have been isolated. From theirkinematics and spatial distribution we conclude that these starsrepresent a sample of RR Lyrae variables in the metal-weak tail of thethick disk that extends to [Fe/H] = -2.05. In the halo samples, thedistribution of V velocities is not Gaussian, even when the metal-weakthick-disk stars are removed. Possibly related, a plot of U and Wvelocities as a function of V velocity for the kinematically unbiasedhalo sample shows some curious structure. The cause of these kinematicanomalies is not clear. In addition, systematic changes to the distancescale within the range of currently accepted values of M_v(RR) are shownto significantly change the calculated halo kinematics. Fainter valuesof M_v(RR), such as those obtained by statistical parallax (~0.60 to0.70 at [Fe/H] = -1.9), result in local halo kinematics similar to thosereported in independent studies of halo kinematics, while brightervalues of M_v(RR), such as those obtained through recent analysis ofHipparcos subdwarf parallaxes (~0.30 to 0.40 at [Fe/H] = -1.9), resultin a halo with retrograde rotation and significantly enlarged velocitydispersions.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | בתולה |
| התרוממות ימנית: | 12h55m10.55s |
| סירוב: | -05°27'32.4" |
| גודל גלוי: | 11.616 |
| תנועה נכונה: | -58.4 |
| תנועה נכונה: | -23.7 |
| B-T magnitude: | 11.644 |
| V-T magnitude: | 11.619 |
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