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A δ Scuti Distance to the Large Magellanic Cloud
We present results from a well-studied δ Scuti star discovered inthe Large Magellanic Cloud (LMC). The absolute magnitude of the variablewas determined from the period-luminosity (P-L) relation for Galacticδ Scuti stars and from theoretical modeling of the observed B,V,Ilight curves with nonlinear pulsation models. The two methods givedistance moduli for the LMC of 18.46+/-0.19 and 18.48+/-0.15,respectively, for a consistent value of the stellar reddening ofE(B-V)=0.08+/-0.02. We have also analyzed 24 δ Scuti candidatesdiscovered in the OGLE II survey of the LMC, and seven variablesidentified in the open cluster LW 55 and in the galaxy disk by Kaluznyand coworkers . We find that the LMC δ Scuti stars define a P-Lrelation whose slope is very similar to that defined by the Galacticδ Scuti variables, and yield a distance modulus for the LMC of18.50+/-0.22 mag. We compare the results obtained from the δ Scutivariables with those derived from the LMC RR Lyrae stars and Cepheids.The corresponding distance moduli are as follows: δ Scuti stars,18.48+/-0.02 mag (standard deviation of the weighted average of thethree above solutions); RR Lyrae stars, 18.49+/-0.06 mag; and Cepheids,18.53+/-0.02 mag. We have assumed an average color excess ofE(B-V)=0.08+/-0.02 mag for both δ Scuti stars and Cepheids. Withinthe observational uncertainties, the three groups of pulsating starsyield very similar distance moduli. These moduli are all consistent withthe ``long'' astronomical distance scale for the Large Magellanic Cloud.Based on data collected at the European Southern Observatory, proposalnumbers 62.N-0802 and 66.A-0485.
| New catalogue of blue stragglers in open clusters
We present a catalogue of blue-straggler candidates in galactic openclusters. It is based on the inspection of the colour-magnitude diagramsof the clusters, and it updates and supersedesthe first version(Ahumada & Lapasset 1995). A new bibliographical search was made foreach cluster, and the resulting information is organised into twotables. Some methodological aspects have been revised, in particularthose concerning the delimitation of the area in the diagrams where thestragglers are selected.A total of 1887 blue-straggler candidates have been found in 427 openclusters of all ages, doubling the original number. The catalogued starsare classified into two categories mainly according to membershipinformation.The whole catalogue (Tables 8, 9, notes, and references) is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/789
| A comprehensive study of the SX Phoenicis star BL Camelopardalis
Context.BL Cam is an extreme field multiperiodic short-periodlow-metallicity high-amplitude SX Phe-type variable where its probablycomplex pulsational content is subject of controversies. Aims.Acomprehensive study has been carried out to investigate the nature andpulsational properties of this object. Methods.The analysis isbased on new photometric data collected during the last few years atdifferent sites, as well as on all available previously published data.Frequency analyses have been performed on a number of reliable data setsto analyse the pulsational content. In addition, the classical O-Cmethod was used to study the behaviour of the main period. Results.Our frequency analysis confirms some aspects on themultiperiodicity of BL Cam, previously found by other authors, showing anumber of secondary modes close to the main frequency f_0=25.5769cd-1. The secondary modes present eventual amplitudevariations. However, the main frequency exhibits no significant changesin its amplitude and seems to correspond to the fundamental mode ofradial pulsation. Abrupt changes sometimes observed in the light curvescould be due to spurious activity on or close to the star's photosphere.We confirm the existence of a secondary frequency at 31.6 or 32.6cd-1, with variable amplitude, and with the possibility ofboth frequencies being intrinsic to the star. More than one hundred ofnew times of light maxima have been determined in the present work.These together with those available in the literature allow us a morediscriminating analysis of the O-C diagram. This shows that the observedvariations of the main period can be described by two terms: (i) asecular increase of the main period at a rate ofdP/Pdt=117(±3)×10-9 yr-1; and (ii) aperturbation from a companion star in a rather eccentric orbit with aperiod of 10.5(±0.2) yr causing a light time semi-amplitude of148(±12) s.
| The role of rotation on Petersen diagrams. The Π1/0 (Ω) period ratios
The present work explores the theoretical effects of rotation incalculating the period ratios of double-mode radial pulsating stars withspecial emphasis on high-amplitude δ Scuti stars (HADS). Diagramsshowing these period ratios vs. periods of the fundamental radial modecan be employed as a good tracer of non-solar metallicities and areknown as Petersen diagrams (PD). In this paper we consider the effect ofmoderate rotation on both evolutionary models and oscillationfrequencies and show that such effects cannot be completely neglected ashas been done until now. In particular we find that differences inperiod ratios of some hundredths can be obtained even forlow-to-moderate rotational velocities (15-50 {km s-1}). Themain consequence is, therefore, the "confusing scenario" generated whentrying to fit the metallicity of a given star using this diagram withoutprevious knowledge of its rotational velocity.
| Pulsational behaviour of the SX Phe variable BL Cam.
The pulsational behaviour of the field high-amplitude SX Phe variable BLCam is investigated here on the basis of new photometric data collectedduring the last few years at different sites together with a revision ofall the available photometric data sets in the literature. Our resultsconfirm the existence of multiperiodicity in this star previously foundby other authors. In addition to the main frequency f_0=25.5769 c/d andits harmonics 2f_0 and 3f_0, with stable amplitude, a secondaryfrequency f_1 exists in the region 31-32 c/d with variable amplitude.Microvariability takes also place in this star, in the region close tof_0, with some additional secondary peaks shown as significant togetherwith some frequency combinations of these modes with f_0.Concerning f_1,it is shown that there is a possibility of the existence of twoindependent peaks (around 31.6 c/d and 32.6 c/d), nonradial and withvariable amplitudes.
| High-amplitude delta Scuti stars in the Galactic Bulge from the OGLE-II and MACHO data .
Searching for main-sequence pulsators, we analyzed photometry of˜200,000 variable star candidates from the OGLE-II Galacticfields, finding 193 high-amplitude delta Scuti stars. This doubles thenumber of known stars of this type. The MACHO data, available for halfof stars, were also analyzed. In our sample of the HADS stars, we found50 multiperiodic objects, including 39 that have period ratios in therange of 0.76-0.80, an indication of the radial fundamental andfirst-overtone pulsation. We discuss the resulting Petersen diagram forthese stars in view of the period ratios predicted by models. Except forstars showing pulsations in the radial fundamental mode and firstovertone, we find the evidence for higher radial overtones andnon-radial modes in the analyzed sample of multiperiodic HADS stars.
| A large and homogeneous sample of SX Phe stars in the Fornax dwarf spheroidal galaxy .
We report on the detection of sixty-one SX Phe stars in the Fornax dwarfspheroidal galaxy using the Wide-Field Imager at the 2.2m ESO-MPItelescope. In spite of their extreme faintness (22.0
| Completing the census of (bright) variable stars in galactic globular clusters .
We present a long-term project aimed at completing the census of(bright) variable stars in Galactic globular clusters. While our mainaim is to obtain a reliable assessment of the populations of RR Lyraeand type II Cepheid stars in the Galactic globular cluster system, dueattention is also being paid to other types of variables, including SXPhoenicis stars, long-period variables, and eclipsing binaries.
| Analysis of main-sequence A-type stars showing radial velocity variability.
We obtained high-resolution spectroscopic data for 33 bright (V < 8)A-type HIPPARCOS programme stars at the ``Observatoire deHaute-Provence'' (OHP) in December 2004. All our targets show someindication of radial velocity variability (Grenier et al, 1999), arelocated in or near the lower part of the Cepheid instability strip, andare poorly studied objects. In this contribution, we present the newdata of the most interesting programme stars and we derive a physicalinterpretation for their variable nature.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
Not Available
| The double-mode nature of the HADS star GSC 00144-03031 and the Petersen diagram of the class
The double-mode pulsation of GSC 00144-03031 has been detected whensearching for COROT targets. A very large dataset composed of 4722photometric measurements was collected at six observatories in Europeand America. There is no hint of the excitation of additional modes(down to 0.6 mmag) and therefore GSC 00144-03031 seems to be a puredouble-mode pulsator, with a very short fundamental radial mode (P = 84min). From uvbyβ photometry and evolutionary tracks it appears tobe a Pop. I star with M = 1.75 Mȯ, located in the middleof the instability strip, close to the Zero-Age Main Sequence. We alsodiscovered other new double-mode pulsators in the databases oflarge-scale projects: OGLE BW2_V142, OGLE BW1_V207, ASAS3 094303-1707.3,ASAS3 000116-6037.0, NSVS 3234596 and NSVS 3324715. An observationalPetersen diagram is presented and explained by means of new models. Acommon sequence connecting Pop. I stars from the shortest to the longestperiods is proposed and the spreads in the period ratios are ascribed todifferent metallicities (at the shortest periods) and to differentmasses (at the longest ones).
| Newly Discovered Variable Stars in the Globular Clusters NGC 5634, Arp 2 and Terzan 8
We report the discovery of a sizeable, previously unknown variable starpopulation in the Sagittarius dwarf spheroidal globular clusters NGC5634, Arp 2 and Terzan 8. Location, preliminary pulsation periods andB-band light curves in relative flux units are provided for all thesestars.
| PSST: The Planet Search Survey Telescope
The Planet Search Survey Telescope is an automated small-aperture CCDimaging photometer designed to search for transits by extrasolar planetsacross the disks of their parent stars. It simultaneously observesthousands of stars with apparent R magnitudes between 10 and 13 in afield approximately 6deg×6deg. Stars in thisbrightness range are well within the capability of the high-precisionradial velocity systems that have successfully detected over 100extrasolar planets to date. The combination of the photometric transitdepth and radial velocity amplitude can provide both the radius of theplanet and a good estimate of its mass, since the orbit is nearlyedge-on. As a result, estimates of the planet's density and otherparameters can be obtained.
| Brh V128 is a double-mode high-amplitude delta Scuti star.
Not Available
| Asteroseismology of HADS stars: V974 Oph, a radial pulsator flavoured by nonradial components
The analysis of a dense time-series on V974 Oph disclosed the richpulsational content (at least five independent terms) of thishigh-amplitude (0.60 mag in B-light) delta Scts star. A mode with afrequency very close to the main one (probably the fundamental radialmode) has been detected: such a doublet is not a common feature in starsof the same class. Also another term can be considered a radial one, butthe high ratio (0.786) raises some problems that can be solved only byadmitting very low metallicity. It is quite evident that someundetectable terms are again hidden in the noise, as the least-squaresfit leaves a rms residual much higher than the observational noise. Allthat considered, nonradial modes seem to play a key rôle in thelight variability of V974 Oph. Revealing an unsuspected asteroseismicinterest, V974 Oph provides a link between low- and high-amplitude deltaScts stars.Based on observations collected at Europan Southern Observatory, LaSilla, Chile
| A New Double-Mode High-Amplitude delta Scuti Star: GSC 2583-00504
CCD-V photometric data show that GSC 2583-00504 is a new high-amplitudedouble-mode Delta Scuti variable with a fundamental period of 0.05172days and a period ratio of 0.773, closely resembling the prototype SXPhe.
| New SX Phoenicis Stars in the Globular Cluster M53
Through time-series CCD photometry of the metal-poor globular clusterM53 we have discovered eight new SX Phoenicis-type stars (labeled``SXP1'' to ``SXP8''). All the new SX Phoenicis stars are located in theblue straggler star region of the color-magnitude diagram of M53. One ofthese stars (SXP2) is found to have very closely separated pulsationfrequencies: f1/f2=0.9595, where f1 andf2 are the primary and secondary frequencies, respectively.This may be due to excitation of nonradial modes. Six of these SXPhoenicis stars are considered to be pulsating in the fundamental mode.They show a tight linear correlation between the period and luminosity.We derive a period-luminosity relation for the fundamental mode for theperiod range of -1.36=-3.010(+/-0.262)logP+15.310(+/-0.048) with an rms scatter of0.038, corresponding to =-3.010logP-1.070 for anadopted distance modulus of (m-M)V=16.38.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| δ Scuti stars and their related objects
δ Scuti stars are a group of stars located on or a little abovethe main sequence of H-R diagram with spectral type from A3 to F5. Theyare low amplitude single or multi period pulsators with period shorterthan 0.3 d. Within the same area there are several groups of variablesor special stars correlated with them, e.g., Dwarf Cepheids, γ Dorvariables, Blue Stragglers, Am stars, Ap stars, ROAp variables, λBoo variables and δ Del variables. In this paper a general reviewin this field, including the number of new variables discovered after1995, is presented. The most reliable period variation rates for all thehigh amplitude variables and several low amplitude variables are listed.Statistic shows the higher the rotation rate v sin i is, the lower thelight variation amplitude is. Thus within young open clusters highamplitude variables cannot be found. The amplitudes-periods distributionhave 3 peaks with the highest of 1.0 mag in V at 0.17 d in period. Forδ Scuti variables in stellar systems the shorter the averageperiod is, the lower the metallicity and the older the age of thestellar system are.
| High-Amplitude δ Scuti and SX Phoenicis Stars: The Effects of Chemical Composition on Pulsations and the Period-Luminosity Relation
We present a theoretical study of the radially pulsating δ Scutiand SX Phoenicis variables, concentrating on the blue straggler SXPhoenicis variables found in globular clusters. We have evolved a gridof stellar models with the metal abundance of the globular cluster M55,including models with alpha-enhanced metal abundances, and tested thesemodels for radial pulsations observed in the high-amplitude δScuti and SX Phoenicis stars. Our grid includes models with globallyenriched helium content to simulate the effects of stellar collisionsand global mixing possible in blue stragglers. We find that globalenrichment of helium strongly affects the temperature and luminosity ofa given star, but the location of the instability strip blue edge andthe slope of the period-luminosity (PL) relation are unchanged. Thissuggests that the PL relation is not affected by blue stragglerformation if blue stragglers are fully mixed stellar mergers. Our blueedges and PL relations are in agreement with other theoreticaldeterminations and also with the observational PL relation of M55, butthey are not in agreement with the PL relation previously derived forhigh-amplitude δ Scuti stars in the field. Analysis of thedouble-mode variable, V41, suggests either that the star may not bepulsating in the first and second overtones as claimed or that normalstellar models may not be accurate models of blue straggler stars.
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| Physical Parameter Determination of the δ Scuti Star V1719 Cygni
New uvbyβ photoelectric photometry of the short-period variablestar V1719 Cygni (HD 200925) has been secured. A period analysis ofthese data and those reported in the literature has provided us withstable pulsation frequencies that fit all the available observationscovering a time span of 20 yr. The frequencies determined are 3.7411556,7.4823111, 11.2234667, and 4.6777749 cycles day-1 and ofsmaller amplitude 8.4189900 cycles day-1. It was found thatthis Population I star has logg around 3.1 and an effective temperatureof 6750 K.
| Period and amplitude variations in the high-amplitude delta Scuti star AE Ursae Majoris
We present a comprehensive investigation of the variations of period andamplitude in the high-amplitude delta Scuti star AE UMa based on our newJohnson V time-series measurements and the existing data. No additionalfrequencies were detected even though all the available data sets from1974 to 2001 were analysed. The light variations of AE UMa can bewell-reproduced with the fundamental and first-overtone radial modes andtheir coupled terms. New observations and analyses support the mostrecent results of Pócs & Szeidl (\cite{pocs}). Thefundamental period was essentially constant over the past 27 years withits standard value of 0fd 086017066 (f_0= 11.625600 cd-1),while the first overtone period decreased at a rate of(1)/(P_1)(dP_1)/(dt) = -4.3x 10-8 yr-1. Theamplitude variations in the two modes of AE UMa are detected at themilli-magnitude level on a time-scale of years. It seems that theamplitudes vary in opposite phases, implying an energy conservation orsome kind of intrinsic variability cause. We deny theover-interpretation of the period change given by Hintz et al.(\cite{hintz97}) and explore its reason. Figure~\ref{Fig:lightcurve} isonly available in electronic form at http://www.edpsciences.org
| Linear Nonadiabatic Properties of SX Phoenicis Variables
We present a detailed linear, nonadiabatic pulsational scenario foroscillating blue stragglers (BSs)/SX Phe variables in Galactic globularclusters (GGCs) and in Local Group (LG) dwarf galaxies. The sequences ofmodels were constructed by adopting a wide range of input parameters andproperly cover the region of the H-R diagram in which these objects areexpected to be pulsationally unstable. Current calculations togetherwith more metal-rich models already presented by Gilliland et al.suggest that the pulsation properties of SX Phe variables are partiallyaffected by metal content. In fact, the pulsation periods for the firstthree modes are marginally affected when moving from Z=0.0001 to 0.006,whereas the hot edges of the instability region move toward coolereffective temperatures by approximately 300-500 K. The inclusion of ametallicity term in the period-luminosity-color (P-L-C) relations causesa substantial decrease in the intrinsic scatter and in the individualerror of the coefficients. This supports the result recently brought outby Petersen & Christensen-Dalsgaard for δ Scuti stars.Moreover, we find that the discrepancy between our relation and similartheoretical and empirical relations available in the literature istypically smaller than 5%. The comparison between theory andobservations in the MV-logP plane as well as in theluminosity amplitude-logP plane does not help to disentangle thelong-standing problem of mode identification among SX Phe stars.However, our calculations suggest that the secular period change seemsto be a good observable to identify the pulsation mode of cooler SX Phevariables. Together with the previous models we also constructed newsequences of models by adopting selected effective temperatures andluminosities along two evolutionary tracks characterized by the samemass value and metal content (M/Msolar=1.2, Z=0.001) butdifferent He contents in the envelope, namely, Y=0.23 and 0.30. The Hecontent in the latter track was artificially enhanced soon after thecentral H exhaustion to mimic, with a crude approximation, thecollisional merging between two stars. Interestingly enough, we findthat the He-enhanced models present an increase in the pulsation periodand a decrease in the total kinetic energy of the order of 20% whencompared with the canonical ones. At the same time, the blue edge of thefundamental mode for the He-enhanced models is approximately 1000 Kcooler than for canonical ones. Moreover, we find that the secularperiod change for He-enhanced models is approximately a factor of 2larger than for canonical ones. According to this evidence, we suggestthat the pulsation properties of SX Phe variables can be soundly adoptedto constrain the evolutionary history of BSs and in turn to single outthe physical mechanisms that trigger their formation.
| SX Phœnicis stars in the core of 47 Tucanae
We present new results on five of six known SX Phœnicis stars inthe core of the globular cluster 47 Tucanae. We give interpretations ofthe light curves in the V and I bands from 8.3 days of observations withthe Hubble Space Telescope near the core of 47 Tuc. The most evolved SXPhe star in the cluster is a double-mode pulsator (V2) and we determineits mass to be (1.54+/-0.05) Msun from its position in theHertzsprung-Russell diagram and by comparing observed periods withcurrent theoretical pulsation models. For V14 we do not detect anypulsation signal. For the double-mode pulsators V3, V15, and V16 wecannot give a safe identification of the modes. We also describe thephotometric techniques we have used to extract the light curves of starsin the crowded core. Some of the SX Phœnicis are saturated and wedemonstrate that even for stars that show signs of a bleeding signal wecan obtain a point-to-point accuracy of 1-3%. Based on observations madewith the NASA/ESA Hubble Space Telescope, obtained at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy Inc., under NASA contractNAS5-26555.
| Stability of pulsation of the double-mode high-amplitude delta Scuti star AE Ursae Majoris
Stability of both the fundamental and first overtone oscillations of AEUMa was investigated by different methods which led to concordantresults. The fundamental period of AE UMa has been essentially constantin the past 60 years consistent with the theoretical expectation (Breger& Pamyatnykh \cite{BP98}). The reported fast period decrease (Hintzet al. \cite{HHJ97}) is shown to be incorrect. The constancy of thefundamental period suggests that the star is in the post-main sequenceevolutionary state as suggested by the evolutionary theories. The firstovertone period is decreasing with a rate of (1/P_1) (dP_1/dt)=-7.310-8 y-1. The fact that the rate of period changefor two modes is quite different indicates that non-evolutionary effectsmay also generate period changes. The changes in amplitude of thefundamental and first overtone were examined by comparing theleast-squares amplitude solution for different segments of observations.Small long-term variations in the amplitudes have occurred in the past25 years.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Cluster AgeS Experiment. CCD photometry of SX Phoenicis variables in the globular cluster M 55
We present CCD photometry of SX Phe variables in the field of theglobular cluster M 55. We have discovered 27 variables, three of whichare probable members of the Sagittarius dwarf galaxy. All of the SX Phestars in M 55 lie in the blue straggler region of the clustercolor-magnitude diagram. Using period ratio information we haveidentified the radial pulsation modes for one of the observed variables.Inspection of the period-luminosity distribution permits the probableidentifications of the pulsation modes for most of the rest of the starsin the sample. We have determined the slope of the period-luminosityrelation for SX Phe stars in M 55 pulsating in the fundamental mode.Using this relation and the HIPPARCOS data for SX Phe itself, we haveestimated the apparent distance modulus to M 55 to be(m-M)_V=13.86+/-0.25 mag.
| delta Scuti and related stars: Analysis of the R00 Catalogue
We present a comprehensive analysis of the properties of the pulsatingdelta Scuti and related variables based mainly on the content of therecently published catalogue by Rodríguez et al.(\cite{retal00a}, hereafter R00). In particular, the primaryobservational properties such as visual amplitude, period and visualmagnitude and the contributions from the Hipparcos, OGLE and MACHOlong-term monitoring projects are examined. The membership of thesevariables in open clusters and multiple systems is also analyzed, withspecial attention given to the delta Scuti pulsators situated ineclipsing binary systems. The location of the delta Scuti variables inthe H-R diagram is discussed on the basis of HIPPARCOS parallaxes anduvbybeta photometry. New borders of the classical instability arepresented. In particular, the properties of the delta Scuti pulsatorswith nonsolar surface abundances (SX Phe, lambda Boo, rho Pup, delta Deland classical Am stars subgroups) are examined. The Hipparcos parallaxesshow that the available photometric uvbybeta absolute magnitudecalibrations by Crawford can be applied correctly to delta Scutivariables rotating faster than v sin i ~ 100 km s{-1} withnormal spectra. It is shown that systematic deviations exist for thephotometrically determined absolute magnitudes, which correlate with vsin i and delta m1. The photometric calibrations are found tofit the lambda Boo stars, but should not be used for the group ofevolved metallic-line A stars. The related gamma Dor variables and thepre-main-sequence delta Scuti variables are also discussed. Finally, thevariables catalogued with periods longer than 0fd 25 are examined on astar-by-star basis in order to assign them to the proper delta Scuti, RRLyrae or gamma Dor class. A search for massive, long-period delta Scutistars similar to the triple-mode variable AC And is also carried out.
| Structural Parameters of DY Pegasi Light Curves between 1949-1986
Structural change of DY Pegasi light curve shape are being studied usingboth traditional and Fourier-type structural parameters. In order toperform this investigation we applied the Fourier decompositiontechnique to each considered data set. The values of the above mentionedstructural parameters were then calculated.
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