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.
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TY Gruis: A Metal-Poor Carbon and Neutron-Capture-Rich RR Lyrae Star
We have conducted a photometric and high-resolution spectroscopicanalysis of the high-latitude (l=1deg, b=-55deg)metal-poor RR Lyrae star TY Gru (=CS 22881-071). We find this star tohave large overabundances of carbon and neutron-capture elements. Masstransfer from an asymptotic giant branch binary companion prior to itsRR Lyrae evolutionary state is the simplest explanation of thiscircumstance. Unfortunately, TY Gru is afflicted by the Blazhko effect,which greatly complicates accurate measurement of the motion of itscenter of mass. We have not yet detected the small orbital motion thatwould be produced by a distant degenerate companion of TY Gru.This paper includes data gathered with the 6.5 m Magellan Telescopeslocated at Las Campanas Observatory, Chile.
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Astrophysics in 2005
We bring you, as usual, the Sun and Moon and stars, plus some galaxiesand a new section on astrobiology. Some highlights are short (the newlyidentified class of gamma-ray bursts, and the Deep Impact on Comet9P/Tempel 1), some long (the age of the universe, which will be found tohave the Earth at its center), and a few metonymic, for instance theterm ``down-sizing'' to describe the evolution of star formation rateswith redshift.
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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.
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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.
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UZ UMa: An RRab star with double-periodic modulation
Our CCD V observations show that the fundamental mode RR Lyrae star UZUMa displays double periodic Blazhko modulation of its light curve. TheBlazhko periods are 26.7 and approx. 143 days. UZ UMa is estimated to bea relatively metal poor RRab star with [Fe/H]=-1.2.
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The GEOS RR Lyr Survey
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How to make progress in the understanding of the Blazhko effect .
Almost a century after its discovery the Blazhko effect in RR Lyraestars remains a mystery. The Blazhko Project is an internationalcollaboration focusing at a better understanding of the phenomenon. Inthis short paper we summarize some of the results obtained so far, andpoint out some of the remaining challenges.
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Blazhko effect and double-mode RR Lyrae stars .
There are two kinds of multi-periodic RR Lyrae stars. The Blazhko effectis a modulation of the primary light cycle that takes place on a typicaltimescale of tens of days. Double-mode RR Lyrae stars pulsatesimultaneously in the fundamental and first overtone radial modes. Thestate of our knowledge of these multi-periodic variables is reviewed.
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Beobachtungskampagne SW Boo, was kam heraus?
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Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
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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.
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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.
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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.
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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].
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The Blazhko behaviour of RR Geminorum I. CCD photometric results in 2004
Extended CCD monitoring of RR Gem revealed that it isa Blazhko type RRab star with the shortest Blazhko period (7.23°)and smallest modulation amplitude (Δ Mmax<0.1 mag)currently known. The short period of the modulation cycle enabled us toobtain complete phase coverage of the pulsation at each phase of themodulation. This is the first multicolour observation of a Blazhko starwhich is extended enough to define accurate mean magnitudes and coloursof the variable at different Blazhko phases. Small, but real, changes inthe intensity mean colours at different Blazhko phases have beendetected. The Fourier analysis of the light curves shows that, in spiteof the mmag and smaller order of the amplitudes, the triplet structureis noticeable up to about the 14th harmonic. The modulation isconcentrated to a very narrow, 0.2 phase range of the pulsation, centredon the supposed onset of the H emission during rising light. Theseobservational results raise further complications for theoreticalexplanation of the long known but poorly understood Blazhko phenomenon.Tables 1-4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http ://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/1049
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Bericht uber die Veranderlichen-Beobachtungswoche an der VdS-Sternwarte in Kirchheim.
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Einige allgemeine Bemerkungen zum Blazhko-Effekt.
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Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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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.
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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.
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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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