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Evolutionary stages and dominant modes in delta Scuti stars .
An examination has been done on the contribution of dominant modes tothe star's light variation. A sample of delta Scuti stars (altogether30 stars) with well-determined frequency solution (based mostly onmultisite international campaigns) are overviewed. Correlation of thedominant (highest amplitude) modes and evolutionary stages have beeninvestigated. Attention is called to the importance of dominant modes inthe theoretical investigations.
| Close frequencies in pulsating stars: common and mysterious! .
Amplitude and phase variability are commonly found in many differenttypes of pulsating stars. This suggests a common, presently unknownphysical origin. We have examined the phenomenon in several delta Scutistars with extensive data and find the beating of close frequencies tobe responsible. This is demonstrated for the star FG Vir by testing therelationship between the observed amplitude and phase variations. Mostclose frequency pairs are situated near the observed or theoreticallypredicted frequencies of radial modes. The large number of detectedclose frequencies excludes the possibility of accidental frequencyagreements.
| A common puzzle for Extreme Helium stars and evolved delta Scuti stars.
The Extreme Helium stars are hot luminous stars of about one solar massthat are believed to be shell He-burning. We modeled the pulsations ofthe hottest ExHe star V2076 Oph, for which the 2000 multisite campaignof Wright et al. detected as many as eight pulsation modes with periodsof 0.4 to 2.5 days. Our shallower envelope-only models predict suchperiods for ℓ=0 and 1. However, if the radiative core is included inthe models, a large number of closely-spaced modes are predicted thatare not observed, since a large number of g-type nodes are present inthe eigenfunctions in the deeper interior. This problem occurs also formodels of evolved shell H-burning delta Scuti stars such as 4 CVn.
| Multimode Resonant Coupling in Pulsating Stars
We consider evolution of an unstable acoustic mode interacting with anensemble of stable g-modes. We show that the static multimode solutiondoes not exist. We then find the condition for the stability of thestatistical equilibrium.Performing numerical integration of amplitude equations for a simplifiedsystem we find that the acoustic mode amplitude exhibits a largeirregular variability on the timescale given by the inverse of thegrowth rate.The g-mode pairs are excited in significantly wider range of detuningparameters than it is implied by the parametric instability criterionapplied to the average amplitude. However, the number of interactingg-mode pairs is reduced because the pairs differing in the detuningparameter by less than their damping rates are synchronized andeffectively act as a single pair.We apply the multimode resonant coupling theory to a realistic stellarmodel. We choose a seismic model of a delta Sct star XX Pyx. Althoughfor some l=2 modes we find amplitudes of the order of a fewmillimagnitudes, the typical amplitudes of low-degree modes are muchhigher. Taking into account the rotational splitting results in decreaseof amplitudes by a factor of few which is not enough to obtainconsistency with observations. We conclude that in this star and likelyin all evolved δ Sct stars, the resonant mode coupling cannot bethe dominant amplitude limiting effect. The nonresonant saturation ofthe driving effect must play the role.
| Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range
We present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to ``thin disk'' and ``thick disk'' components cannot besupported with the present data.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Non-adiabatic theoretical observables in δ Scuti stars
Phase differences and amplitude ratios at different colour photometricbands are currently being used to discriminate pulsation modes tofacilitate mode identification of κ-driven non-radial pulsatingstars. In addition to physical inputs (e.g., mass, T_eff, etc.), thesequantities depend on the non-adiabatic treatment of the atmosphere. Thispaper presents theoretical results concerning δ Scuti pulsatingstars. The envelope of each of these stellar structures possesses aconvection zone whose development is determined by various factors. Aninteracting pulsation-atmosphere physical treatment is introduced whichsupplies two basic non-adiabatic physical quantities: the relativeeffective temperature variation and the phase lag φT,defined as the angle between effective temperature variation and radialdisplacement. These quantities can be used to derive the phasedifferences and amplitude ratios. Numerivalues for these quantitiesdepend critically on the α MLT parameter used to calculate theconvection in the envelope. The dependence on α was analyzed andit was found that the use of colour observations may be of considerableimportance in testing the MLT. Finally, examples are given of howα introduces uncertainties in the theoretical predictionsregarding phases and amplitudes of photometric variations in δScuti pulsating stars.
| Variable stars in the globular cluster NGC 3201 - I. Multimode SX Phe type variables
We report on the discovery of 11 multimode SX Phoenicis type bluestragglers in the field of the southern globular cluster NGC 3201. Inthese variables both radial and non-radial modes are excited. For threevariables the derived period ratio is close to that observed in SXPhoenicis itself, suggesting that these stars are pulsating in thefundamental and the first-overtone radial modes. Using the McNamaraperiod-luminosity relation we have estimated the apparent distancemodulus to NGC 3201 to be 14.08 +/- 0.06 +/- 0.1 mag.
| Mt. Dushak-Erekdag Observatory: A Chance to Close the Asian Gaps in WET Coverage
The Mt. Dushak-Erekdag Observatory (Central Asia, Turkmenistan,58deg E longitude) is located just in the longitudes gap ofasteroseismological networks. It is the southernmost observatory of theformer Soviet Union, its latitude is +38deg . The sky seeingat the site is one of the best in Central Asia: a low light pollution,high and stable sky transparency, over 200 usable nights per year. Thealtitude is above 2000 m. Odessa Astronomical Observatory has its 0.8 mtelescope with a two-star high-speed photometer there, which frequentlyparticipates in international programs and multi-site campaigns. Anaccuracy of the photometry amounts to 1 mmag. Besides, a 1 m wide-angletelescope and a dual-tube telescope with 0.5 m mirrors are installed atthe observatory. The developed infrastructure at the site and thestable economy in Turkmenistan make the Mt. Dushak-Erekdag Observatoryvery interesting for the WET observations.
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731
| Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalog
This paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/721
| 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.
| Pulsation of the δ Scuti star θ2 Tau: new multisite photometry and modelling of instability
The results of a multisite photometric campaign of θ2Tau are reported. This binary system consists of an evolved and amain-sequence A star, both situated inside the instability strip. The12th Delta Scuti Network campaign included 152 h of high-precisionphotometry obtained at four observatories. This leads to the derivationof 11 frequencies of pulsation in the 10.8 to 14.6 cycle d-1range. These frequencies confirm the results from previous Earth-based(1982-1986) as well as satellite (2000) photometry, although amplitudevariability on a time-scale of several years is present. We show that atleast two high frequencies (26.18 and 26.73 cycle d-1) arealso present in θ2 Tau. Arguments are given that thesehigh frequencies originate in the main-sequence companion and are notcombination frequencies, fi+fj, from the primary.Models for both the primary and the secondary components were checkedfor the instability against radial and non-radial oscillations. All hotmodels of the primary with Teff > 8000 K are stable in theobserved frequency range. The best fit between the theoretical andobserved frequency ranges is achieved for models with Teff~7800 K (or slightly higher), in agreement with photometric calibrations.The instability range spans two or three radial orders in the rangep4 to p6 for radial modes. Post-main-sequencemodels (with or without overshooting) are preferable for the primary,but main-sequence models with overshooting cannot be excluded. For theless-luminous secondary component the instability range is wider andspans 5 to 7 radial orders from p2 to p8. Theobserved frequencies lie around radial modes p5 top6. The main uncertainties of these results are caused by asimple treatment of the convective flux in the hydrogen ionization zone.
| BVRJK Photometry and a Spectroscopic Study of the Algol Short-Period Binary VV Ursae Majoris
We present the first light curves in the infrared J and K filters of VVUMa and analyze them, together with a new set of BVR light curvesobtained in different runs from 1997 to 2000. Based on the spectra of VVUMa and standard stars in the region 8440-8870 Å, we classify theprimary component of the binary as a type A1.5-2 V star. Evidence ofperiodic small-amplitude variations in the brightness of the system isfound and is more clear during the secondary eclipse orbital phases. Aperiodicity of about 0.51 hr is in good agreement with a previousfinding based on Strömgren photometry, pointing to a real origin inthe system, presumably on low-amplitude pulsations of the primary star.The analysis of the BVRJK light curves, using a code based on ATLASmodel atmospheres, yields new orbital and stellar parameters. We deriveeffective temperatures Teff=9250+/-150 K andTeff=5600+/-100 K for the primary and secondary star,respectively. We challenge the current view that VV UMa is a system withunusually low mass components for their spectral type, and analternative solution is proposed, allowing masses of the stars in theexpected range for their spectral types that are in reasonable agreementwith the available photometric and spectroscopic data. From thevisual-infrared photometry we find no evidence of a significant infraredexcess in the system, deriving an interstellar reddeningE(B-V)<=0.10.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Long term behaviour of the double-mode high-amplitude delta Scuti star RV Arietis
Stability of both the fundamental and first overtone oscillations of RVAri was investigated by different methods which led to concordantresults. The fundamental period of RV Ari has been decreasing veryslowly with a rate of (1/P0)(dP0/dt)=-0.6x10-8 y-1 while the first overtone period has beenincreasing a little faster with a rate of(1/P1)(dP1/dt) =+0.9x 10-8y-1, if we assume linear period changes over the past 65years. Although the very slow change in the periods is consistent withthe evolutionary theories, the fact that the signs of the period changesfor the two modes are opposite indicates that the dominating part of theperiod variation may be the result of non-evolutionary effects. Theamplitudes of the fundamental and overtone oscillations have undergonesmall changes (several mmag) on a time scale of years, and a slightincrease in the amplitude of the first overtone pulsation is suspected.An additional frequency at f2=13.6116 cd-1 isfound. Table 2 is only available in electronic form at\http://www.edpsciences.org
| On the Period-Luminosity-Colour-Metallicity relation and the pulsational characteristics of lambda Bootis type stars
Generally, chemical peculiarity found for stars on the upper mainsequence excludes delta Scuti type pulsation (e.g. Ap and Am stars), butfor the group of lambda Bootis stars it is just the opposite. This makesthem very interesting for asteroseismological investigations. The groupof lambda Bootis type stars comprises late B- to early F-type,Population I objects which are basically metal weak, in particular theFe group elements, but with the clear exception of C, N, O and S. Thepresent work is a continuation of the studies by Paunzen et al.(\cite{Pau97}, \cite{Pau98}), who presented first results on thepulsational characteristics of the lambda Bootis stars. Since then, wehave observed 22 additional objects; we found eight new pulsators andconfirmed another one. Furthermore, new spectroscopic data (Paunzen\cite{Pau01}) allowed us to sort out misidentified candidates and to addtrue members to the group. From 67 members of this group, only two arenot photometrically investigated yet which makes our analysis highlyrepresentative. We have compared our results on the pulsationalbehaviour of the lambda Bootis stars with those of a sample of deltaScuti type objects. We find that at least 70% of all lambda Bootis typestars inside the classical instability strip pulsate, and they do sowith high overtone modes (Q < 0.020 d). Only a few stars, if any,pulsate in the fundamental mode. Our photometric results are inexcellent agreement with the spectroscopic work on high-degree nonradialpulsations by Bohlender et al. (\cite{Boh99}). Compared to the deltaScuti stars, the cool and hot borders of the instability strip of thelambda Bootis stars are shifted by about 25 mmag, towards smaller(b-y)_0. Using published abundances and the metallicity sensitiveindices of the Geneva 7-colour and Strömgren uvbybeta systems, wehave derived [Z] values which describe the surface abundance of theheavier elements for the group members. We find that thePeriod-Luminosity-Colour relation for the group of lambda Bootis starsis within the errors identical with that of the normal delta Scutistars. No clear evidence for a statistically significant metallicityterm was detected. Based on observations from the Austrian AutomaticPhotoelectric Telescope (Fairborn Observatory), SAAO and Siding SpringObservatory.
| Close frequency pairs in Delta Scuti stars
The majority of the well-studied delta Scuti stars shows frequency pairsin the power spectra with frequency separations less than 0.06cd-1 (0.7 mu Hz) as well as amplitude variability. We examinethe interpretation in terms of separate excited stellar pulsation modes,single modes with variable amplitudes, and observational problems. Thevariable-phase technique, which examines the phase jumps near the timesof minimum amplitude of an assumed single frequency, is applied to theextensive data of the star BI CMi, which shows some of the most extremebehavior. The following results are found for the 5 features in thepower spectrum which could be explained as single modes with variableamplitudes or as double modes: for three features it can be shown thatthese are indeed pairs of separate pulsation modes beating with eachother: at times of minimum amplitude the phase jumps are observed andboth the observed amplitude and phase variations can be predictedcorrectly by assuming two separate modes of nearly equal frequencies.Artifacts caused by observational error, insufficient frequencyresolution or variable amplitudes can be ruled out. A fourth pair has aprobable origin in two excited modes, while a 5th case is inconclusivedue to long time scales of variability and small amplitudes. Theexistence of close frequency needs to be taken into account in planningthe lengths of earth-based as well as space campaigns so that sufficientfrequency resolution is obtained. Possible reasons for the existence ofclose frequencies in delta Scuti stars are considered. They include thedense frequency spacing caused by the presence of mixed modes,rotational splitting as well as near-coincidence of the frequencies ofmodes with different l values (the so-called Small Spacing).
| Asteroseismology of δ Scuti Stars: A Parameter Study and Application to Seismology of FG Virginis
We assess the potential of asteroseismology for determining thefundamental properties of individual δ Scuti stars. We computed agrid of evolution and adiabatic pulsation models using the Yale RotatingEvolution Code to study the systematic changes in low-order (l=0, 1, 2,and 3) modes as functions of fundamental stellar properties. Changes tothe stellar mass, chemical composition, and convective core overshootinglength change the observable pulsation spectrum significantly. Ingeneral, mass has the strongest effect on evolution and on pulsationfollowed by the metal abundance. Changes to the helium content have verylittle effect on the frequencies until near the end of the mainsequence. Changes to each of the four parameters change the p-modefrequencies more, in both absolute and relative terms, than they do theg- and mixed-mode frequencies, suggesting that these parameters have agreater effect on the outer layers of the star. We also presentevolution and pulsation models of the well-studied star FG Virginis,outlining a possible method of locating favorable models in the stellarparameter space based on a definitive identification of only two modes.Specifically, we plot evolution models on the (period-period ratio) and(temperature-period ratio) planes to select candidate models and modifythe core overshooting parameter to fit the observed star. For thesetests, we adjusted only the mass, helium and metal abundances, and coreovershooting parameter, but this method can be extended to include theeffects of first-order rotational splitting and second-order rotationaldistortion of pulsation spectra.
| The Wolfgang and Amadeus Automatic Photoelectric Telescopes. A ``Kleine-Nacht-Musik'' during the first five years of routine operation
We present a summary of five years of continuous operation of theUniversity of Vienna twin Automatic Photoelectric Telescopes (APTs) --Wolfgang and Amadeus. These two telescopes are part of the FairbornObservatory facility located in the Sonoran desert close to WashingtonCamp in southern Arizona. The detection and distinction procedurebetween weather-induced data-quality loss and systematic data-qualityloss turned out to be a crucial task. Therefore, special emphasis islaid on the data quality monitoring tools developed throughout theyears. Furthermore, we summarize the scientific highlights from thefirst five years of operation
| Radial and Nonradial Oscillations of 44 Tauri
Evolutionary stellar models of 44 Tauri, a multiperiodic δ Scutistar, have been developed theoretically and compared with earlierobservational reports. The models depict 44 Tau at thehydrogen-shell-burning stage, when it is in radiative equilibrium with avery thin surface convective layer. Using the models, we performedcalculations to obtain radial and nonradial adiabatic oscillationfrequencies, and the equations were treated linearly. The results showedthat the radial fundamental (6.899 cycles day-1) andfirst-overtone (8.961 cycles day-1) frequencies and the fivenonradial modes of low harmonic degree that had been determinedtheoretically were in agreement with the observed values of previousauthors to an accuracy of a few parts in 103. However, adifference emerged in the nonradial frequencies, which we classified asg-modes of low harmonic degree, whereas the observational reports hadclassified them as p-modes. In addition, even though 44 Tau has arotation vsini=6.8 km s-1 (according to Solano and Fernley),which we considered negligible, we analyzed the effect of rotation. Ourfindings revealed that rotation modulated the oscillation frequencies ofthe nonrotating model on the order of 10-2.
| 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
| Multimode delta Scuti stars in the open cluster NGC 7062
The central field of NGC 7062 was observed intensively with the maingoal of finding delta Scuti stars suitable for use inasteroseismological tests of stellar structure and evolution theory. BVtime series photometry was obtained for this northern open cluster,which has a large population of stars inside the delta Scuti instabilitystrip, making it a probable host of several such variables. We reportfindings of 15 pulsating stars, including at least 13 delta Scuti stars.Ten variables oscillate in two or more frequencies. Only one of thesevariables was known before, for which we detected 9 frequencies. Fiveprobable variables are mentioned, and period analysis is given for all20 stars. Based on observations obtained at the Nordic OpticalTelescope, operated on the island of La Palma jointly by Denmark,Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio delRoque de los Muchachos of the Instituto de Astrofisíca deCanarias.
| 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
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| Sixth Vienna Workshop in Astrophysics: Delta Scuti and Related Stars
Not Available
| The multiperiodic δ Scuti star 4 Canum Venaticorum: amplitude variability
Recent multisite campaigns of the Delta Scuti Network have revealed 34frequencies of pulsation for the star 4 CVn. Our present knowledge ofthe frequencies makes it possible to reanalyse the shorter data sets inthe literature, photometric observations from 1966 to 1997. 4 CVn showsstrong amplitude variability with time-scales of ten years or longer,although for neighbouring years the amplitudes usually are similar.Seven of the eight dominant modes show annual variability of ~12 percent. The variability increases to ~40 per cent over a decade. Theformally derived time-scale of variation of 30 years can only be a roughestimate, since this is also the length of the available data span. Thevariability is compared with that of FG Vir, which shows lower amplitudevariability. The cyclic behaviour of the amplitude variations excludesan evolutionary origin. There exists some evidence that a mode at6.12d-1, which appeared during 1996 and 1997, may have beenpresent with small amplitudes in the 1976-1978 time period. Thepulsation mode at 7.375d-1 exhibited the most rapid decreasefound so far: the V amplitude dropped from the highest known value of15mmag in 1974 to 4mmag in 1976 and 1mmag in 1977. After that the modehas been increasing in amplitude. There exists a phase jump between 1976and 1977, suggesting the growth of a new mode. It is interesting to notethat this mode also has the strongest coupling with other modes withcombination frequencies, fi+/-fj. The amplitudesof these combination frequencies are also strongly variable from year toyear. We speculate that power is transferred between the modes throughmode-coupling.
| On the Variability of F1-F9 Luminosity Class III-V Stars
Hipparcos Satellite photometry of F1-F9 luminosity class III-V starsindicates that most are not particularly variable. A few stars for whichfurther study is desirable are identified.
| Asteroseismology of Delta Scuti Stars
This paper presents recent results for delta Scuti stars based onmeasurements obtained by WET/Delta Scuti Network as well as theoreticalmodeling of the pulsation modes. In particular, the two stars indifferent stages of evolution, FG Vir and 4 CVn, are discussed. For 4CVn, the XCOV13 campaign has revealed 34 frequencies, which sets a newrecord for delta Scuti stars. Preliminary mode identifications arepresented, indicating pulsation in low radial order and low degree (l =0 to 2). The star shows strong amplitude variability with timescales often years or longer, although for neighbouring years the amplitudesusually are similar. The cyclic behavior of the amplitude variationsexcludes an evolutionary origin. The pulsation mode at 7.375 c/dexhibits the most rapid decrease found so far: the V amplitude droppedfrom the highest known value of 15 mmag in 1974 to 4 mmag in 1976 and 1mmag in 1977. After that the mode has been increasing in amplitude.There exists a phase jump between 1976 and 1977, suggesting the growthof a new mode.
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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