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Einfuhrung quadratischer Lichtwechselelemente.
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| 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
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| 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
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| The GEOS RR Lyr Survey
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| The Shortest Modulation Period Blazhko RR Lyrae Star: SS Cancri
Extended BV(RI)C CCD observations of SS Cnc, a short-periodRRab star, are presented. Nearly 1400 data points in each band have beenobtained, spanning over 79 days during the spring of 2005. The starexhibits light-curve modulation, the so-called Blazhko effect, withsmall amplitude (B maximum brightness varies by 0.1 mag) and with theshortest modulation period (5.309 days) ever observed. In the Fourierspectrum of the V light curve, the pulsation frequency components aredetected up to the 24th harmonic order, and modulation sidelobefrequencies with significantly asymmetric amplitudes are seen up to the15th and 9th orders for the lower and higher frequency components,respectively. A detailed comparison of the modulation behavior of SS Cncand RR Gem, two recently discovered small-amplitude,short-modulation-period Blazhko stars, is presented. The modulationfrequency (fm) appears in the Fourier spectrum of both starswith similar amplitude. We also demonstrate that the modulationfrequencies have basically different properties from those of thepulsation and modulation sidelobe frequencies, indicating that thephysics behind these frequency components is not the same. The discoveryof small amplitude modulations of RRab stars cautions that the largephotometric surveys (MACHO and OGLE) may seriously underestimate thenumber of modulated RR Lyrae stars.
| 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.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
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| Pulkovo compilation of radial velocities for 35495 stars in a common system.
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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.
| 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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| 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 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
| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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| The GEOS RR Lyr Survey
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| Image-Subtraction Photometry of the Globular Cluster M3: Identification of New Double-Mode RR Lyrae Stars
We have applied the image subtraction method of Alard and Lupton to theextensive M3 data set previously analyzed by Corwin and Carney usingDAOPHOT and ALLSTAR. This new analysis has produced light curves andperiods for 15 variables not found in the previous study but alreadyknown to be variables, and it has also resulted in improved periods forseveral other variables. The additional variables recovered with theimage subtraction analysis are in the very central region of M3, wherecrowding is severe and the photometry was not of sufficient quality thatit could be put on the standard system. The present study brings to 222the total number of RR Lyrae variables in Corwin and Carney's M3 dataset for which light curves and periods are available. Among them we haveidentified three new candidate double-mode pulsating variables (V13,V200, and V251), reported here for the first time. This brings to eightthe total number of double-mode RR Lyrae (RRd's) identified in M3. Ofthe newly discovered RRd's V13 is unusual in that it has the fundamentalas the dominant pulsation mode. M3 is unique among the globular clustersin having RRd variables with a dominant fundamental mode. Two of the newcandidate RRd's (V13 and V200) have period ratios as low as 0.738-0.739.They lie well separated from all previously known double-mode variablestars in the Petersen diagram in positions implying a large spread inmass and/or, less likely, in heavy element mass fraction, among the M3horizontal-branch (HB) stars. We explore mass transfer and heliumenhancement as possible explanations for the apparent spread in HBmasses. We also note that the masses derived from the double-modeanalyses now favor little mass loss on the red giant branch. We findthat V200 has changed its dominant pulsation mode from fundamental tofirst overtone, while V251 has changed its dominant mode from firstovertone to fundamental in the interval 1992 to 1993. Together withM3-V166 this is the first time that double-mode variables are observedto switch their dominant pulsation modes while remaining RRd's. Thephenomenon is found to occur in a 1 yr time span, thus suggesting thatthese stars are undergoing a rapid evolutionary phase and that bothredward and blueward evolution may take place among the HB stars in theOosterhoff type I cluster M3. The unusual behavior of the M3 RRd's isdiscussed in detail and compared with that of the double-mode RR Lyraeidentified so far in globular clusters and in the field of our and otherLocal Group galaxies. We find a lack of correlation between the presenceof RRd variables and any of the cluster structural parameters.
| Unterschiedliche Helligkeitsauspragungen des Blazhko-Effectes.
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| Photoelectric Maxima of Selected Pulsating Stars
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| 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.
| Zur qualitat der visuellen Beobachtung kurzperiodisch Veranderlicher.
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| Times of Light Maxima of Some RRab Stars
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| BVI Time-Series Data of the Galactic Globular Cluster NGC 3201. I. RR Lyrae Stars
We present Johnson BV- and Kron-Cousins I-band time-series datacollected over three consecutive nights in a region of 13arcmin2 centered on the Galactic globular cluster (GGC) NGC3201. The time sampling of current CCD data allowed us to deriveaccurate light curves and, in turn, mean magnitudes and colors for asample of 53 RR Lyrae stars. To overcome the thorny problem ofdifferential reddening affecting this cluster, we derived new empiricalrelations connecting the intrinsic B-V and V-I colors of fundamental(RRab) RR Lyrae stars to the luminosity amplitude, the metallicity, andthe pulsation period. The key features of these relations are thefollowing: (1) they rely on stellar parameters, which are not affectedby reddening; (2) they supply accurate estimates of intrinsic colorsacross the fundamental instability strip and cover a wide metallicityrange; (3) they were derived by neglecting the RR Lyrae stars that areaffected by amplitude modulation. Moreover, the zero point of the E(B-V)reddening scale was empirically checked using the large sample of RRLyrae stars in M3 from Corwin & Carney, a GGC affected by avanishing reddening. According to these relations we estimatedindividual reddenings for RR Lyrae stars in our sample and the mainresults we found are the following: (1) The mean cluster reddening basedon E(B-V) color excesses is =0.30+/-0.03. This estimate isslightly higher than the mean reddening evaluations available in theliterature or based on the dust infrared map by Schlegel, Finkbeiner,& Davis, i.e., =0.26+/-0.02. Note that the angularresolution of this map is ~6', whereas for current reddening map it is~1'. (2) The mean cluster reddening based on E(V-I) color excesses is=0.36+/-0.05. This estimate is only marginally inagreement with the mean cluster reddening obtained using the reddeningmap by von Braun & Mateo and derived by adopting cluster turnoffstars, i.e., =0.25+/-0.07. On the other hand, currentintrinsic spread among individual reddenings (~0.2 mag) agrees quitewell with the estimate provided by previous authors. It is noteworthythat previous mean cluster reddenings are in very good agreement withvalues obtained using the empirical relations for intrinsic RR Lyraecolors provided by Kovacs & Walker. (3) According to currentindividual E(B-V) and E(V-I) reddenings and theoretical predictions forhorizontal-branch stars, we found that the true distance modulus forthis cluster is 13.32+/-0.06 mag. This determination is somehowsupported by the comparison between predicted and empirical pulsationamplitudes. (4) The comparison between present luminosity amplitudes andestimates available in the literature discloses that approximately 30%of fundamental RR Lyrae stars are affected by amplitude modulation (theBlazhko effect). This finding confirms empirical evidence originallybrought out by Szeidl and by Smith. Based on observations collected atthe European Southern Observatory, La Silla, Chile.
| Blazhko stars: Always distorted?
A reexamination of the amplitude ratios of the photometric and radialvelocity changes of Blazhko RRab stars in their different Blazhko phasesshows that a normal amplitude ratio occurs near the phase of maximumamplitude. Checking the Fourier parameters of maximum amplitude lightcurves with different methods proved, however, that none of these lightcurves can be regarded as a normal RR Lyrae type light curve.
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