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Observational constraints on the magnetic field of RR Lyrae stars
Context: A high percentage of the astrophysically important RR Lyraestars show a periodic amplitude and/or phase modulation of theirpulsation cycles. More than a century after its discovery, this“Blazhko effect” still lacks acceptable theoreticalunderstanding. In one of the plausible models for explaining thephenomenon, the modulation is caused by the effects of a magnetic field.So far, the available observational data have not allowed us to eithersupport nor rule out the presence of a magnetic field in RR Lyrae stars.Aims: We intend to determine whether RR Lyrae stars are generallycharacterized by the presence of a magnetic field organized on a largescale. Methods: With the help of the FORS1 instrument at the ESOVLT we performed a spectropolarimetric survey of 17 relatively brightsouthern RR Lyrae stars, both Blazhko stars and non-modulated stars, anddetermined their mean longitudinal magnetic field with a typical errorbar <30 G. Results: All our measurements of the meanlongitudinal magnetic field resulted in null detections within 3?.From our data we can set an upper limit for the strength of the dipolecomponent of the magnetic fields of RR Lyrae stars to ~130 G. Because ofthe limitations intrinsic to the diagnostic technique, we cannot excludethe presence of higher order multipolar components. Conclusions:The outcome of this survey clarifies that the Blazhko modulation in thepulsation of RR Lyrae stars is not correlated with the presence of astrong, quasi-dipolar magnetic field.
| 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.
| Multiperiodic Galactic field RR Lyrae stars in the ASAS catalogue
The All Sky Automated Survey (ASAS) monitors bright stars (8 < V <14 mag) south of declination +28°. The ASAS Catalogue of VariableStars (ACVS) presently contains 50099 objects; among them are 2212objects classified as RR Lyrae pulsating variables. We use ASASphotometric V-band data to search for multiperiodicity in those stars.We find that 73 of 1435 RRab stars and 49 of 756 RRc stars exhibit theBlazhko effect. We observe a deficiency of RRab Blazhko variables withmain pulsation periods greater than 0.65 d. The Blazhko periods of RRcstars exhibit a strongly bimodal distribution. During our study wediscovered the Blazhko effect with multiple periods in object ASAS050747-3351.9 = SU Col. Blazhko periods of 89.3 and 65.8 d and acandidate of 29.5 d were identified with periodogram peaks near thefirst three harmonics of the main pulsation. These observations mayinspire new models of the Blazhko effect, which has eluded a consistenttheory since its discovery about one hundred years ago. Long-term lightcurve changes were found in 29 stars. We also found 19 Galactic doublemode pulsators (RRd), of which four are new discoveries, raising thenumber of ASAS discoveries of such objects to 16, out of 27 known in thefield of our Galaxy.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
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.
| Absolute Magnitudes and Kinematic Parameters of the Subsystem of RR Lyrae Variables
The statistical parallax technique is applied to a sample of 262 RRabLyrae variables with published photoelectric photometry, metallicities,and radial velocities and with measured absolute proper motions.Hipparcos, PPM, NPM, and the Four-Million Star Catalog (Volchkov et al.1992) were used as the sources of proper motions; the proper motionsfrom the last three catalogs were reduced to the Hipparcos system. Wedetermine parameters of the velocity distribution for halo [(U_0, V_0,W_0) = (-9 +/- 12, -214 +/- 10, -16 +/- 7) km/s and (sigma_U, sigma_V,sigma_W) = (164 +/- 11, 105 +/- 7, 95 +/- 7) km/s] and thick-disk [(U_0,V_0, W_0) = (-16 +/- 8, -41 +/- 7, -18 +/- 5) km/s and (sigma_U,sigma_V, sigma_W) = (53 +/- 9, 42 +/- 8, 26 +/- 5) km/s] RR Lyrae, aswell as the intensity-averaged absolute magnitude for RR Lyrae of thesepopulations: = 0.77 +/- 0.10 and = +1.11 +/-0.28 for the halo and thick-disk objects, respectively. The metallicitydependence of the absolute magnitude of RR Lyrae is analyzed(=(0.76 +/- 0.12) + (0.26 +/- 0.26) x ([Fe/H] + 1.6) = 1.17 +0.26 x [Fe/H]). Our results are in satisfactory agreement with the_(RR)-[Fe/H] relation from Carney et al. (1992)(_(RR) = 1.01 + 0.15 x [Fe/H]) obtained by Baade-Wesselink'smethod. They provide evidence for a short distance scale: the LMCdistance modulus and the distance to the Galactic center are 18.22 +/-0.11 and 7.4 +/-±0.5 kpc, respectively. The zero point ofthe distance scale and the kinematic parameters of the RR Lyraepopulations are shown to be virtually independent of the source ofabsolute proper motions used and of whether they are reduced to theHipparcos system or not.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| The absolute magnitudes of RR Lyraes from HIPPARCOS parallaxes and proper motions
We have used HIPPARCOS proper motions and the method of StatisticalParallax to estimate the absolute magnitude of RR Lyrae stars. Inaddition we used the HIPPARCOS parallax of RR Lyrae itself to determineit's absolute magnitude. These two results are in excellent agreementwith each other and give a zero-point for the RR Lyrae M_v,[Fe/H]relation of 0.77+/-0.15 at [Fe/H]=-1.53. This zero-point is in goodagreement with that obtained recently by several groups usingBaade-Wesselink methods which, averaged over the results from thedifferent groups, gives M_v = 0.73+/-0.14 at [Fe/H]=-1.53. Taking theHIPPARCOS based zero-point and a value of 0.18+/-0.03 for the slope ofthe M_v,[Fe/H] relation from the literature we find firstly, thedistance modulus of the LMC is 18.26+/-0.15 and secondly, the mean ageof the Globular Clusters is 17.4+/-3.0 GYrs. These values are comparedwith recent estimates based on other "standard candles" that have alsobeen calibrated with HIPPARCOS data. It is clear that, in addition toastrophysical problems, there are also problems in the application ofHIPPARCOS data that are not yet fully understood. Table 1, whichcontains the basic data for the RR Lyraes, is available only at CDS. Itmay be retrieved via anonymous FTP at cdsarc.u-strasbg.fr (130.79.128.5)or via the Web at http://cdsweb.u-strasbg.fr/Abstract.html
| Early evolution of the Galactic halo revealed from Hipparcos observations of metal-poor stars
The kinematics of 122 red giant and 124 RR Lyrae stars in the solarneighborhood are studied using accurate measurements of their propermotions obtained by the Hipparcos astrometry satellite, combined withtheir published photometric distances, metal abundances, and radialvelocities. A majority of these sample stars have metal abundances of(Fe/H) = -1 or less and thus represent the old stellar populations inthe Galaxy. The halo component, with (Fe/H) = -1.6 or less, ischaracterized by a lack of systemic rotation and a radially elongatedvelocity ellipsoid. About 16 percent of such metal-poor stars have loworbital eccentricities, and we see no evidence of a correlation between(Fe/H) and e. Based on the model for the e-distribution of orbits, weshow that this fraction of low-e stars for (Fe/H) = -1.6 or less isexplained by the halo component alone, without introducing the extradisk component claimed by recent workers. This is also supported by theabsence of a significant change in the e-distribution with height fromthe Galactic plane. In the intermediate-metallicity range, we find thatstars with disklike kinematics have only modest effects on thedistributions of rotational velocities and e for the sample at absolutevalue of z less than 1 kpc. This disk component appears to constituteonly 10 percent for (Fe/H) between -1.6 and -1 and 20 percent for (Fe/H)between -1.4 and -1.
| Radial velocities and iron abundances of field RR Lyraes. II.
This is the second of the papers devoted to derive radial velocities andiron abundances of field RR Lyraes observed by HIPPARCOS. Our abundancesshow good agreement with those in the literature obtained both fromphotometric (Delta S index) and spectroscopic methods. Binary candidatesand stars misclassified as RR Lyraes in the original HIPPARCOS list havebeen also identified. Appendix is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u- strasbg.fr/Abstract.html
| Accurate Positions Of Variable Stars Near The South Galactic Pole
Not Available
| AH Cam: A metal-rich RR Lyrae star with the shortest known Blazhko period
Analysis of 746 new V-band observations of the RR Lyrae star AH Camobtained during 1989 - 1992 clearly show that its light curve cannot bedescribed by a single period. In fact, at first glance, the Fourierspectrum of the photometry resembles that of a double-mode pulsator,with peaks at a fundamental period of 0.3686 d and an apparent secondaryperiod of 0.2628 d. Nevertheless, the dual-mode solution is a poor fitto the data. Rather, we believe that AH Cam is a single-mode RR Lyraestar undergoing the Blazhko effect: periodic modulation of the amplitudeand shape of its light curve. What was originally taken to be the periodof the second mode is instead the 1-cycle/d alias of a modulationsidelobe in the Fourier spectrum. The data are well described by amodulation period of just under 11 d, which is the shortest Blazhkoperiod reported to date in the literature and confirms the earliersuggestion by Goranskii. A low-resolution spectrum of AH Cam indicatesthat it is relatively metal rich, with delta-S less than or = 2. Itshigh metallicity and short modulation period may provide a critical testof at least one theory for the Blazhko effect. Moskalik's internalresonance model makes specific predictions of the growth rate of thefundamental model vs fundamental period. AH Cam falls outside the regimeof other known Blazhko variables and resonance model predictions, butthese are appropriate for metal-poor RR Lyrae stars. If the theorymatches the behavior of AH Cam for a metal-rich stellar model, thiswould bolster the resonance hypothesis.
| The metallicity of RR Lyrae stars in Baade's window
Metallicities are derived via the Delta S method for 59 RR Lyraevariables in the Baade's window field of the Galactic nuclear bulge.Both RRab and RRc variables have average Fe/H = -1.0. The metallicitydistribution for the whole sample is sharply peaked, with a dispersionin Fe/H of only 0.16 dex, far smaller than suggested by previousstudies. The narrow metallicity distribution does not permit the variouscurrent estimates of the magnitude of a luminosity/metallicity relationfor RR Lyrae stars to be distinguished. It is also found that the metalabundance of the globular cluster NGC 6522 in Baade's window is close tothat of the bulge RR Lyraes, which sets the reddening to the Baadewindow to be E(B - V) = 0.50 + or - 0.05 and the distance to thegalactic center to be 8.2 + or - 1 kpc.
| Period analysis of the RR Lyrae star RU PISCIUM
RU Psc is a c-type RR Lyrae star (period P = 0.39 d) known for irregularcycle-to-cycle brightness variations and a possible 28 d Blazhko period.Using proven period-finding techniques over 1100 extant photometricobservations were analyzed to see if RU Psc might also be a double-modeRR Lyrae star of the kind recently discovered in the globular clusters M15, M 3, and IC 4499 (Cox et al. 1983; Clement et al. 1986), and in theDraco dwarf galaxy (Nemec 1985). It is concluded that the peculiaritiesseen in the photometry of RU Psc are due primarily to rapid andirregular period changes, and are not due to low-amplitude oscillationscaused by a secondary period.
| A spectroscopic study of the c-type RR Lyraes
Image tube scanner observations have been made for a sample of fieldc-type RR Lyraes. Using these spectra, it is shown how Preston's metalabundance indicator Delta-S can be applied to the RRc's to derive (Fe/H)on Butler's system. Mean temperatures for the field RRc's based onreddening free colors determined from the strength of the H-beta line.These abundances and temperatures allow the delineation of Oosterhoffgroups among field stars. It is shown that, as in clusters, theOosterhoff effect for field stars occurs star by star and not just formean properties of the group. There is a temperature region in thefield-star instability strip where the RRc's and RRab's can both existat the same temperature. Data on the temperature boundaries of theinstability strip provide no convincing case for helium abundancedifferences among field RR Lyraes with differing metal abundances.
| Four-color photometry of short-period variable stars.
Abstract image available at:http://adsabs.harvard.edu/abs/1973AJ.....78...83E
| On the 95 RR Lyrae stars.
Not Available
| Benennung von veränderlichen Sternen
Not Available
| 115 neue Veränderliche
Not Available
| 25 New Variable Stars, Principally in Harvard Maps 39 and 45.
Not Available
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