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Observational Evidence of Convective Cycles as the Cause of the Blazhko Effect in RR Lyrae Stars
Among RR Lyrae stars displaying the Blazhko effect, a few show no periodmodulation in spite of striking changes in their light amplitudes. Thisanomalous behavior and the mean period of the affected variables arepredicted correctly by the theory of slow convective cycles in thestellar envelope.
| 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.
| Korrekturen zu Vorhersagen im BAV Circular 2008.
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| The Blazhko behavior of RV UMa
RV UMa is one of the most extensively studied RR Lyrae stars showingBlazhko modulation. Its photometric observations cover more than 90years. The published photoelectric observations of RV UMa obtained atthe Konkoly Observatory (Kanyó 1976) were re-considered andcompleted with previously unpublished data. During the time interval ofthe observations the periods of both the pulsation and the modulationvaried within the ranges of 0.000007 and 0.9 days, respectively. We havefound a definite but not strict inverse relation between the pulsationand modulation periods of RV UMa.
| The GEOS RR Lyr Survey
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| The Blazhko behaviour of RR Geminorum II. Long-term photometric results
Context: RR Gem is one of the few Blazhko RR Lyraethat has photometric observations available extended enough to study thelong-term courses of its pulsation and modulation properties in detail. Aims: We investigate the pulsation and modulation properties and therelations between them in RR Gem using photometricobservations from the past 70 years in order to gain further insightinto the nature of the Blazhko modulation. Methods: We studied thephotographic, photoelectric, and CCD light curves obtained at theKonkoly Observatory and other authors' published maxima observations.Detailed analysis of the light curves, maximum brightness, and O-C dataare carried out. Results: RR Gem showed modulationmost of the time it was observed. The modulation amplitude showed strongvariations from the undetectable level (less than 0.04 mag in maximumbrightness) to about 0.20 mag. The amplitudes of the amplitude and phasemodulations showed parallel changes, thus the total “power”of the modulation have changed during the past 70 years. Parallelchanges in the pulsation and modulation periods occur with adP_mod/dP_puls = 1.6 ± 0.8 × 103 ratio. We alsodetected 0.05-0.1 mag changes in the mean maximum brightness and meanpulsation amplitude.Tables 4-15 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/469/1033
| The GEOS RR Lyr Survey
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| A Search for Random Cycle-to-Cycle Period Fluctuations in Five ? Scuti, SX Phoenicis, and RR Lyrae Variables
Random cycle-to-cycle period fluctuations in pulsating stars were firststudied by Eddington and Plakidis in 1929, and have subsequently beenfound in almost all Mira stars, many RV Tauri stars, and a few Cepheids.They complicate the use of (O-C) diagrams for studying evolutionary period changes in these stars. We set out to study such fluctuations in four ? Scuti stars and SX Phoenicis stars; we added one RR Lyrae star for testing purposes. We discuss complications that arise in applying this method to short-period stars. Only one of the five stars -- the SX Phoenicis star XX Cyg -- showed statistically-significant fluctuations.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| The Blazhko effect of RR Lyrae in 2003-2004
Aims.Extensive photometry of RR Lyr was obtained over a 421-day intervalin 2003-2004, covering more than 10 Blazhko cycles in a multisitecampaign. The length and density of this data set allow for a detailedanalysis. Methods: .We used Fourier techniques to study RR Lyr'sbehavior over the pulsation and the Blazhko cycle. We propose atwo-frequency model for decomposing the frequency spectrum.Results: .The light variations were fitted with the main radialfrequency, its harmonics up to 11th order, and the detected tripletfrequencies. No significant quintuplet components were found in thefrequency spectrum. Given the total time span of the measurements, wecan now unambiguously conclude that the Blazhko period has becomenotably shorter than the previously known value of 40.8 days, whereasthe main pulsation period remained roughly the same. Changes in themodulation period have been reported for other well-studied Blazhkovariables. They challenge the explanations for the Blazhko effect whichlink the modulation period directly to the rotation period. The newphotometry reveals an interval in the pulsation cycle of RR Lyr duringwhich the star's intensity barely changes over the Blazhko cycle. Thisinterval occurs during the infalling motion and between the supposedphases of the early and the main shock. The data also permit a moredetailed study of the light curve shape at different phases in theBlazhko period through Fourier parameters.
| 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.
| The GEOS RR Lyr Survey
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| [Fe/H] derived from the light curves of RR Lyrae stars in the Galactic halo
Context: .The iron abundance of halo RR Lyrae stars can provideimportant information about the formation history of the Galactichalo. Aims: .We determine the [Fe/H] of the sample of halo RRabstars by using the P-ϕ31-[Fe/H] relation developed byJurcsik & Kovács based on their light curves. We need toextend the relation from the V band to our unfiltered CCD band. Methods: .To do this, we use the low-dispersion spectroscopic [Fe/H] ofliteratures and the photometric data released by the first-generationRobotic Optical Transient Search Experiment (ROTSE-I) project. We doregression analyses for the calibrating sample using a linear functionand test its validity by comparing of the predicted [Fe/H] with thespectroscopic [Fe/H]. In general, the fit accuracy for the two different[Fe/H] is better than 0.19 dex. Results: . We derive an empiricalP-ϕ31-[Fe/H] linear relation for the unfiltered CCD band(ROTSE-I), i.e. [ Fe/H]=-3.766-5.350P+1.044ϕ31. In ourtest, the P-ϕ31-[Fe/H] relation is also fit for ourunfiltered CCD band. In addition, another linear relation,ϕ31_V=0.882+0.792ϕ31_W, is also derivedfor the transformation between the V and W bands. We present thepredicted [Fe/H] of the sample (the 31 halo RRab stars) in a catalog. Conclusions: . The mean [Fe/H] of the sample is -1.63 with dispersionof 0.45 dex in distribution, which is consistent with the resultsderived from the blue horizontal branch star candidates by Kinnman etal. (2000, A&A, 364, 102). The mean [Fe/H] values of the RRab starsin the range of 1 kpc, 2 kpc, and 3 kpc from the star 91 (a double-modeRR Lyrae star), are all lower than that of the background halo stars.These values are consistent with that of star 91 suggested by Wu et al.(2005, AJ, 130, 1640), which indicates they might have a common origin.
| 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.
| On the Distribution of the Modulation Amplitudes of Blazhko Type RRab Stars
Using all available data on the modulation properties of Blazhko RRabvariables connection has been found between the pulsation period and theamplitude of the modulation. The possible largest value of themodulation amplitude, defined as the sum of the Fourier amplitudes ofthe first four modulation frequency components, increases towardsshorter period variables.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| 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
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| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| The GEOS RR Lyr Survey
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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].
| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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| The GEOS RR Lyr Survey
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| The Changing Blazhko Effect of XZ Cygni
New CCD photometry has been obtained for the RR Lyrae variable star XZCygni. An analysis of old and new photometry confirms earlier resultsthat XZ Cyg exhibits the Blazhko effect and that its Blazhko period haschanged over time. These changes in the Blazhko period areanticorrelated with observed changes in the primary period of XZ Cyg.During the first half of the 20th century, XZ Cyg had a Blazhko periodof approximately 57.4 days. Beginning in 1965, its primary periodunderwent a steep decline in several steps. Coincidentally, its Blazhkoperiod increased to about 58.5 days. In 1979, the primary periodsuddenly increased again. After an interval in which the Blazhko effectwas small, the Blazhko effect reestablished itself, with a period ofapproximately 57.5 days. When its Blazhko period is near 57.5 days, XZCyg has also shown a tertiary period of 41.6 days. We confirm that thereis evidence for a longer 3540 day period in photometry obtained duringthe first half of the 20th century. XZ Cyg is compared with three otherRR Lyrae stars that also appear to show changing Blazhko periods. Theobserved changes in the length of the Blazhko period of XZ Cyg constrainpossible explanations for the Blazhko effect. In particular, they argueagainst any theoretical explanation that requires that the Blazhkoperiod be exactly equal, or directly proportional, to the rotationperiod of the star.
| No evidence of a strong magnetic field in the Blazhko star RR Lyrae
In this paper we report a new series of high-precision (medianσB 80 G) longitudinal magnetic field measurementsof RR Lyrae, the brightest Blazhko star, obtained with the MuSiCoSspectropolarimeter over a period of almost 4 years from 1999-2002. Thesedata provide no evidence whatsoever for a strong magnetic field in thephotosphere of RR Lyrae, a result consistent with Preston's(\cite{Preston67}) results, but inconsistent with apparent magneticfield detections by Babcock (\cite{Babcock58}) and Romanov et al.(\cite{Romanov87}, \cite{Romanov94}). Following discussion of thesedisparate results, we conclude that RR Lyrae is a {bona fide}non-magnetic star, a conclusion which leads to the general falsificationof models of the Blazkho effect requiring strong photospheric magneticfields. Furthermore, due to the 4 year baseline of our observations, wecan also dismiss the hypothesis that RR Lyrae undergoes a 4-year``magnetic cycle''. Therefore the origin of the observed 4-yearmodulation of RR Lyrae remains unexplained, and we stress the need foradditional theoretical efforts to come to a better understanding of thisphenomenon.Based on observations obtained with the MuSiCoS spectropolarimeterattached to the 2 m Bernard-Lyot Telescope of the Pic du MidiObservatory, France.
| Unterschiedliche Helligkeitsauspragungen des Blazhko-Effectes.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
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| Photoelectric Maxima of Selected Pulsating Stars
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Observation and Astrometry data
| Constellation: | Dragon |
| Right ascension: | 19h09m42.60s |
| Declination: | +64°51'32.2" |
| Apparent magnitude: | 10.177 |
| Proper motion RA: | 9.2 |
| Proper motion Dec: | 3.6 |
| B-T magnitude: | 10.552 |
| V-T magnitude: | 10.208 |
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