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Known Galactic field Blazhko stars
A list of known Galactic field stars exhibiting Blazhko effectcontaining 242 stars is presented. All the entries including theirdesignations, positions, pulsation, and Blazhko periods were collectedfrom the available literature. The actual values of parameters aregiven.
| The All-sky GEOS RR Lyr Survey with the TAROT Telescopes: Analysis of the Blazhko Effect
We used the GEOS database to study the Blazhko effect of galactic RRabstars. The database is continuously enriched by maxima supplied byamateur astronomers and by a dedicated survey by means of the two TAROTrobotic telescopes. The same value of the Blazhko period is observed atdifferent values of the pulsation periods and different values of theBlazhko periods are observed at the same value of the pulsation period.There are clues suggesting that the Blazhko effect is changing from onecycle to the next. The secular changes in the pulsation and Blazhkoperiods of Z CVn are anticorrelated. The diagrams of magnitudes againstphases of the maxima clearly show that the light curves of Blazhkovariables can be explained as modulated signals, both in amplitude andin frequency. The closed curves describing the Blazhko cycles in suchdiagrams have different shapes, reflecting the phase shifts between theepochs of the brightest maximum and the maximum O - C. Our sampleshows that both clockwise and counterclockwise directions are possiblefor similar shapes. The improved observational knowledge of the Blazhkoeffect, in addition to some peculiarities of the light curves, has yetto be explained by a satisfactory physical mechanism.
| Blazhko RR Lyrae light curves as modulated signals
We present an analytical formalism for the description of Blazhko RRLyrae light curves. In this formalism the amplitude and frequencymodulations are treated in a manner similar to the theory of electronicsignal transmission. We consider monoperiodic RR Lyrae light curves tobe carrier waves, and modulate their amplitude (AM), frequency (FM) andphase (PM); as a general case we discuss simultaneous AM and FM. Themain advantages of this method are the following: (i) the mathematicalformalism naturally explains numerous light-curve characteristics foundin the Blazhko RR Lyrae stars such as mean brightness variations,complicated envelope curves and non-sinusoidal frequency variations;(ii) our elucidation also explains the properties of the Fourier spectrasuch as apparent higher order multiplets, amplitude distribution of thesidepeaks, the appearance of the modulation frequency itself and itsharmonics. In addition, compared to the traditional methods, ourlight-curve solutions reduce the number of necessary parameters. Thisformalism can be applied to any type of modulated light curves, not justto Blazhko RR Lyrae star light curves.
| The CoRoT star 105288363: strong cycle-to-cycle changes of the Blazhko modulation
We present an analysis of the COnvection, ROtation and planetaryTransits (CoRoT) star 105288363, a new Blazhko RR Lyrae star of typeRRab (f0= 1.7623 d-1), observed with the CoRoTspacecraft during the second long run in the direction of the GalacticCentre (LRc02, time-base 145 d). The CoRoT data are characterized by anexcellent time-sampling and a low noise amplitude of 0.07 mmag in the2-12 d-1 range and allow us to study not only the finedetails of the variability of the star, but also long-term changes inthe pulsation behaviour and the stability of the Blazhko cycle. We use,among other methods, standard Fourier analysis techniques and O-Cdiagrams to investigate the pulsational behaviour of the Blazhko star105288363. In addition to the frequency pattern expected for a BlazhkoRR Lyrae star, we find an independent mode (f1= 2.984d-1) showing a f0/f1 ratio of 0.59which is similar to that observed in other Blazhko RR Lyrae stars. Thebump and hump phenomena are also analysed, with their variations overthe Blazhko cycle. We carefully investigated the strong cycle-to-cyclechanges in the Blazhko modulation (PB= 35.6 d), which seem tohappen independently and partly diametrically in the amplitude and phasemodulations. Furthermore, the phasing between the two types ofmodulations is found to change during the course of the observations.
| Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| Long-term photometric monitoring of Messier 5 variables - II. Blazhko stars
The light curves of 50 RRab (RR0) stars in M5 collected in Szeidl et al.(Paper I) are investigated to detect Blazhko modulation. 18 Blazhkostars are identified, and modulation is suspected in two additionalcases. The mean pulsation period of Blazhko stars is 0.04 d shorter thanthe mean period of the entire RRab sample in M5. Among the RRab starswith period shorter than 0.55 d the incidence rate of the modulation isas high as 60 per cent. The mean B-V colours of Blazhko stars overlapwith the colours of first overtone RRc (RR1) pulsators. The mean Vmagnitudes of Blazhko stars are on the average 0.05-mag fainter thanthose of the RRab stars with stable light curves. Blazhko stars tend tobe situated close to the zero-age horizontal branch at the blue edge ofthe fundamental-mode instability strip in M5. We speculate that thisspecific location hints that the Blazhko effect may have an evolutionaryconnection with the mode switch from the fundamental to theovertone-mode pulsation.
| The multiperiodic Blazhko modulation of CZ Lacertae
A thorough analysis of the multicolour CCD observations of the RRab-typevariable, CZ Lacertae, is presented. The observations were carried outin two consecutive observing seasons in 2004 and 2005 within theframework of the Konkoly Blazhko Survey of bright, northern,short-period RRab variables. The O - C variation of CZ Lac indicatedthat a significant period decrease took place just around the time ofthe CCD observations. Our data gave a unique opportunity to study therelated changes in the pulsation and modulation properties of a Blazhkostar in detail. Two different period components (≈ 14.6 and ≈ 18.6d) of the Blazhko modulation were identified. Both modulation componentshad similar strength. The periods and amplitudes of the modulationschanged significantly from the first season to the next, while the meanpulsation amplitude decreased slightly. The modulation frequencies werein a 5:4 resonance ratio in the first observing season, and then thefrequencies shifted in opposite directions, and their ratio was close tothe 4:3 resonance in the next season. The interaction of the twomodulations caused beating with a period of 74 d in the first season,which resembled the 4-yr-long cycle of the ≈ 40-d modulation of RRLyr. The mean values of the global physical parameters and their changeswith the Blazhko phase of both modulation components were determined bythe inverse photometric method. Based on observations collected with theautomatic 60-cm telescope of Konkoly Observatory, Budapest,Svábhegy.
| Kepler photometry of the prototypical Blazhko star RR Lyr: an old friend seen in a new light
We present our analysis of the long-cadence Kepler data for thewell-studied Blazhko star RR Lyr, gathered during the first two quartersof the satellite's observations and covering a total of 127 d. Besidesbeing of great importance for our understanding of RR Lyrae stars ingeneral, these RR Lyr data can be regarded as a case study forobservations of bright stars with Kepler. Kepler can performhigh-precision photometry on targets like RR Lyr, as the saturated fluxis conserved to a very high degree. The Kepler data on RR Lyr arerevolutionary in several respects. Even with long-cadence sampling (onemeasurement per 29.4 min), the unprecedented precision (< mmag) ofthe Kepler photometry allows the study of the star's extreme light-curvevariations in detail. The multiplet structures at the main frequency andits harmonics, typical for Blazhko stars, are clearly detected up to thequintuplets. For the first time, photometric data of RR Lyr reveal thepresence of half-integer frequencies, linked to a period-doublingeffect. This phenomenon may be connected to the still unexplainedBlazhko modulation. Moreover, with three observed Blazhko cycles at ourdisposal, we observe that there is no exact repetition in thelight-curve changes from one modulation cycle to the next for RR Lyr.This may be due to additional periodicities in the star, or to transientor quasi-periodic changes.
| Recent Maxima of 64 Short Period Pulsating Stars
This paper contains times of maxima for 64 short period pulsating stars(primarily RR Lyrae and d Scuti stars). This represents a portion of theCCD observations received by the AAVSO Short Period Pulsator (SPP)section through December 2009.
| 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.
| 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.
| First CoRoT light curves of RR Lyrae stars. Complex multiplet structure and non-radial pulsation detections in V1127 Aquilae
Context. The CoRoT - Convection Rotation and planetary Transits - spacemission is a great opportunity for monitoring stars with excellenttime-sampling and unprecedented photometric precision for up to 150days. As an important benefit, high-quality RR Lyrae light curves areobtained with a quasi-uninterrupted coverage over several pulsation andBlazhko cycles. Aims: The Blazhko effect in RR Lyrae stars is anunsolved problem of astrophysics. We used the high-precision space datato contribute more precise knowledge to explain the possible physicalprocesses behind the phenomenon. Methods: We applied differentperiod-finding techniques including Period04, MuFrAn, PDM and SigSpec.Amplitude and phase modulation were investigated by an analyticalfunction method as well as with the traditional O-C diagrams. Results: The Blazhko modulation frequency is directly detected in thespectrum, as well as its first and second harmonics. It shows thenon-linear nature of the Blazhko modulation. Besides the triplets,further higher-order modulation side peaks appear around the pulsationfrequency as quintuplet, septuplet, nonuplet, undecaplet, tredecaplet,quindecaplet and sepdecaplet structures. Additional frequencies, notbelonging to the classical multiplet structures, are detected, as wellas their linear combinations with the fundamental radial mode. Weinterpret these additional terms as non-radial modes. During the fiveconsecutive Blazhko cycles, there is a shift of the maximum phase around0.011 pulsation phase which is likely the consequence of a long termmodulation.Full Table 1 is 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/510/A39The CoRoT spacemission was developed and is operated by the French space agency CNES,with participation of ESA's RSSD and Science Programmes, Austria,Belgium, Brazil, Germany, and Spain.
| 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.
| An extensive photometric study of the Blazhko RR Lyrae star DM Cyg
DM Cyg, a fundamental mode RRab star, was observed in the 2007 and 2008seasons in the framework of the Konkoly Blazhko Survey. Very smallamplitude light-curve modulation was detected with 10.57d modulationperiod. The maximum brightness and phase variations do not exceed0.07mag and 7min, respectively. In spite of the very small amplitude ofthe modulation, beside the frequency triplets characterizing the Fourierspectrum of the light curve, two quintuplet components were alsoidentified. The accuracy and the good phase coverage of our observationsmade it possible to analyse the light curves at different phases of themodulation separately. Utilizing the inverse photometric Baade-Wesselinkmethod, we could detect very small systematic changes in the global meanphysical parameters of DM Cyg during its Blazhko cycle. The detectedchanges are similar to what we have already found for a large modulationamplitude Blazhko variable, MW Lyrae. The amplitudes of the detectedchanges in the physical parameters of DM Cyg are only about 10 per centof those that have been found in MW Lyr. This is in accordance with itssmall modulation amplitude being about one-tenth of the modulationamplitude of MW Lyr.The pulsation period of DM Cyg has been increasing by a rate of ? =0.091dMyr-1 during the hundred-year time base of theobservations. Konkoly archive photographic observations indicate thatwhen the pulsation period of the variable was shorter by?ppuls = 5 × 10-6d the modulationperiod was longer by ?pmod = 0.066d than today.Based on observations collected with the automatic 60cm telescope ofKonkoly Observatory, Svábhegy, Budapest.E-mail: jurcsik@konkoly.hu
| A photometric study of the southern Blazhko star SS For: unambiguous detection of quintuplet components
We present our analysis of photometric data in the Johnson B and Vfilter of the southern Blazhko star SS For. In parallel, we analysed theV observations obtained with the All Sky Automated Survey-3 photometryof the star gathered between 2000 and 2008. In the frequency spectraresulting from a Fourier analysis of our data, the triplet structure isdetectable up to high order, both in the B and V data. Moreover, we findevidence for quintuplet components. We confirm from our data that themodulation components decrease less steeply than the harmonics of themain frequency. We derived the variations of the Fourier parametersquantifying the light-curve shape over the Blazhko cycle. There is goodagreement between the spectroscopic abundance and the metallicitydetermined from the Fourier parameters of the average light curve. SSFor is peculiar as a Blazhko star because of its strong variationsaround minimum light.
| BAV-Results of Observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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.
| BAV-Results of observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| An extensive photometric study of the Blazhko RRLyrae star MWLyr - I. Light-curve solution
We have obtained the most extensive and most accurate photometric dataof a Blazhko variable MWLyrae (MWLyr) during the 2006-2007 observingseasons. The data within each 0.05 phase bin of the modulation period(Pm = f-1m) cover the entire lightcycle of the primary pulsation period (P0 =f-10), making possible a very rigorous andcomplete analysis. The modulation period is found to be 16.5462d, whichis about half of that was reported earlier from visual observations.Previously unknown features of the modulation have been detected.Besides the main modulation frequency fm, sidelobe modulationfrequencies around the pulsation frequency and its harmonics appear at+/-2fm, +/-4fm and +/-12.5fmseparations as well. Residual signals in the pre-whitened light curvelarger than the observational noise appear at the minimum-risingbranch-maximum phase of the pulsation, which most probably arise fromsome stochastic/chaotic behaviour of the pulsation/modulation. TheFourier parameters of the mean light curve differ significantly from theaverages of the Fourier parameters of the observed light curves in thedifferent phases of the Blazhko cycle. Consequently, the mean lightcurve of MWLyr never matches its actual light variation. TheΦ21,Φ31 phase differences in differentphases of the modulation show unexpected stability during the Blazhkocycle. A new phenomenological description of the light-curve variationis defined that separates the amplitude and phase (period) modulationsutilizing the phase coherency of the lower order Fourier phases.
| The unique frequency spectrum of the Blazhko RRc Star LS Her
The Blazhko effect in RR Lyrae stars is still poorly understoodtheoretically. Stars with multiple Blazhko periods or in which theBlazhko effect itself varies are particularly challenging. This studyinvestigates the Blazhko effect in the RRc star LS Her. Detailed CCDphotometry in the V, RC and IC band has beenperformed on 63 nights during six months. LS Her is confirmed to have aBlazhko period of 12.75 +/- 0.02 d. However, where normally the sidefrequencies of the Blazhko triplet are expected, an equidistant group ofthree frequencies is found on both sides of the main pulsationfrequency. As a consequence, the period and amplitude of the Blazhkoeffect itself vary in a cycle of 109 +/- 4 d. LS Her is a unique objectturning out to be very important in the verification of the theories forthe Blazhko effect.
| 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.
| First Quintuplet Frequency Solution of a Blazhko Variable: Light Curve Analysis of RV UMa
RV UMa is one of the RRab stars showing regular large-amplitudelight-curve modulation. Extended photoelectric observations of RV UMaobtained at the Konkoly Observatory were published by Kanyó, andthe data were analysed by Kovács. After detecting an error in thereduction procedure of the published Konkoly data, corrected photometricdata are presented with additional, previously unpublished measurements.The re-analysis of the combination of the corrected Konkoly datasupplemented by Preston & Spinrad's observations has led to thediscovery that the appropriate mathematical model of the light curve is,in fact, a quintuplet frequency solution, rather than, a triplet. Thisfinding has crucial importance in the interpretation of the Blazhkophenomenon, as a triplet (doublet) is the preferred structure inresonance models, quintuplet in magnetic models. Period changes of boththe pulsation and modulation light variations of RV UMa have beendetected based on its century-long photometric observations. An overallanticorrelation between the pulsation and modulation period changes canbe defined by dPBl /dP 0 = -8.6 ×104 gradient, i.e., the modulation period is longer if thepulsation period is shorter. Between 1946 and 1975 the pulsation andmodulation periods showed, however, parallel changes, which points tothe fact that there is no strict relation between the changes in theperiods of the pulsation and modulation.
| Einstieg in die Veraenderlichenbeobachtung.
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
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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
Not Available
| 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 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.
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