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Публикации по объекту
A Complicated Pulsation δ Scuti Variable in Praesepe: HD 74028
We report the pulsation characteristics of the δ Scuti star HD74028, a low-amplitude pulsator in the Praesepe cluster. Amplitudespectra of 126 hr of observations spanning 16 nights indicatemultiperiodic pulsation behavior. We identify three frequencies,f1=22.6652, f2=23.8505, and f3=20.5254cycles day-1, and find four additional candidate frequencies,f4=17.3060, f5=12.0643, f6=14.8160, andf7=17.1143 cycles day-1. This complicatedfrequency distribution requires an explanation that includes rotationalsplitting.
| Zero-Age Main Sequence in the HR Diagram of the Vilnius Photometric System
The zero-age main sequence for solar metallicity stars in the absolutemagnitude vs. color diagram of the Vilnius seven-color photometricsystem is determined. The calibration is based on the results ofphotoelectric photometry of stars in the Hyades, Pleiades and Praesepeopen clusters and the Ori OB1 association. A theoretical Victoria-Reginaisochrone, corresponding to an age of 10 million years, coincides wellwith the lower envelope of the unevolved main sequence.
| 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
| 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.
| delta Scuti stars in Praesepe I. The STACC 1998 campaign - the photometry
We present the results of the multisite differential CCD photometry forthe two delta Scuti stars, BN and BV Cnc, in the open cluster Praesepe.The main objective was to identify the character of the pulsation modesin BN Cnc deriving their accurate periods, amplitudes and phases. Theseparameters are essential for the mode identification which uses combinedphotometric and spectroscopic data and is presented in the secondarticle. For BN Cnc, six pulsation modes with amplitudes above thedetection limit ( ~ 0.5 mmag) were detected. Using the same CCD framesit was possible to verify the presence of the four pulsation modes in BVCnc, the faintest of delta Scuti stars in Praesepe. It is shown that inthis very low-amplitude pulsator, substantial amplitude variations areseen between 1997 and 1998. Based in part on observations obtained atthe European Southern Observatory at La Silla, Chile (Application60D-0148).
| 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
| 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.
| 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
| Binaries in the Praesepe and Coma Star Clusters and Their Implications for Binary Evolution
This completes a study of the evolution of binary systems in five openclusters of various ages. Among 21 stars observed in Praesepe, eight arefound or confirmed to be spectroscopic binaries and orbital elements arederived, while one more shows long-term binary motion. Among 18 starsobserved in the Coma Berenices cluster, five are found or confirmed tobe spectroscopic binaries and orbital elements are derived, while asixth has tentative elements. Among five clusters studied we searchedfor three expected evolutionary effects, namely an increase with age inthe mass ratios, a decrease with age of the binary periods, and anincrease in binary frequencies. We find that there is a progression (atthe 3 sigma level) from no binaries out of 10 with mass ratios greaterthan 0.5 in the youngest cluster (combined with the published resultsfor NGC 6193) to 25% such stars in the intermediate-age clusters to 43%such stars in these two oldest clusters. There is no evidence for anincrease in short-period binaries with age. And there is slight evidence(at the 1 sigma level) for an increase with age from 15% to 28% in thefraction of large-amplitude binaries. These results are mostlyconsistent with the idea that most binaries are formed or modified inthree-body interactions, and successive generations of formation anddisruptions tend to form binaries with larger mass ratios. However, partof the initial generation of binaries is probably primordial.
| Photometric parameters for rotating models of A- and F-type stars
We have computed the photometric magnitudes of rotatingatmospheres-based on the simple model of Collins-for a grid suitable formain-sequence and slightly evolved stars of spectral type A0 to F5. Agravity-darkening law valid for radiative and convective envelopes hasbeen considered. The general results are given as magnitude differencesbetween rotating and non-rotating copartners to allow for the use of anyphotometric calibration. A simple interpolation on these results givesthe photometric parameters for interior rotating models but we alsoindicate how they can be used to correct for the effect of rotation whenan investigation with non-rotating models is carried out. We illustratethe procedure with the interesting case of the Praesepe Cluster.
| Amplitude investigation of delta Scuti variables in open clusters
We report here the results of a statistical analysis of 28 delta Scutistars from five open clusters, alpha Persei, Pleiades, Hyades, Praesepeand Coma. These delta Scuti variables, most of which are on the mainsequence, tend to show a positive correlation between oscillationamplitude and absolute luminosity. No correlation is found betweenamplitude and effective temperature.
| Seismology of delta Scuti stars in the Praesepe cluster. I. Ranges of unstable modes as predicted by linear analysis versus observations
We consider here a representative set of delta Scuti stars observed inthe Praesepe cluster, thanks to recent efforts of multi-site networks.We show that the effect of rotation on the determination of fundamentalparameters {Mbol} and {Teff} cannot be neglectedwhen modelling fast rotators as delta Scuti stars. We propose a methodto take this effect into account and gain some indication on therotation rate of the stars. We then use this unique homogeneous set ofobservational data to investigate the pulsational behaviour of deltaScuti stars for different masses, corresponding to differentevolutionary stages at the age of the Praesepe cluster. We propose herean alternative approach to seismology of delta Scuti stars, trying toavoid specific but questionable mode identifications. Via a large set ofmodels, we compare the observed modes with the unstable modes asobtained from a linear stability analysis including a nonlocaltime-dependent treatment of convection. We show that, in the frameworkof the linear analysis adopted here, a satisfying agreement can bereached between the predicted ranges of unstable modes and the rangesderived from observations. However we found that for ``low-mass'' deltaScuti stars (1.6-1.80 Msun) the agreement is found only for arestricted range of values of the mixing length parameter. These starsthus bring a valuable observational constraint on the description of theconvection in the outer layers of stars.
| Pulsation, binarity and close frequency spacing in $delta Scuti ta$ Scuti stars: BQ and BW Cancri. Results of the STEPHI VI campaign in Praesepe Cluster
New pulsation modes in two delta Scuti stars of Praesepe cluster, BQ andBW Cnc, have been detected during the STEPHI VI campaign in 1995. Inparticular, 3 frequencies for BQ Cnc and 9 frequencies for BW Cnc havebeen found above a 99% confidence level. The possibility of the presenceof a g-mode present in BQ Cnc is discussed, considering its binarity.The effect of mutual interference between very close detectedfrequencies in BW Cnc during the observations, is also considered. Thislast effect reveals the necessity of long-period observing runs, inorder to avoid its influence in the final number of detected modes. Insuch situation, studies of secular amplitude changes can be stronglyaffected.
| Photometry and asteroseismology of delta Scuti stars in Praesepe
We discuss observations and seismic analyses for three multi-periodicdelta Scuti stars in the Praesepe cluster: BU, BN and BV Cnc. For twostars (BU and BN Cnc) we re-analyse published photoelectric photometryand show that using statistical weights results in a dramatic reductionin the noise level. We detect seven frequencies in BU Cnc and eight inBN Cnc, with three of the latter being previously unknown. We alsopresent new time-series CCD observations of BN and BV Cnc thatsuccessfully demonstrate high-precision differential photometry onstrongly defocussed images. The observations show that BV Cnc is amulti-periodic variable, with at least four oscillation frequencies.Finally, we compare the observed oscillation frequencies in the threestars with models and derive luminosities, effective temperatures andmasses.
| Seismology of delta Scuti stars in the Praesepe cluster. II. Identification of radial modes and their associated stellar parameters
An analysis based on a comparison between observations and stellarmodels has been carried out to identify radial modes of oscillations inseveral multi-periodic delta Scuti stars of the Praesepe cluster (BU,BN, BW and BS Cnc). The assumption that all the stars considered havecommon parameters, such as metallicity, distance or age, is imposed as aconstraint. Even so, there is a large number of possible solutions,partially caused by the rotational effects on the pulsation frequenciesand on the stars' positions in the HR diagram, which need to beparameterized. When pairs of radial modes are assumed to be present inevery star, only a few similar identifications are found to be possible,corresponding to a metallicity of Z ~ 0.030 and an amount ofovershooting of alpha_ov ~ 0.20. They are associated with a distancemodulus of ~ 6.43 and an age of ~ 650 Myr. Estimates of mass androtation rates for each star are also deduced.
| The Age Range of Hyades Stars
On the basis of canonical models, the age of Hyades supercluster stars,whether in the Hyades and Praesepe clusters or the noncluster field,ranges from (5-6) x 10^8 to 10^9 yr. The difference between the parallaxderived from the supercluster motion and that obtained from Hipparcosobservations has a dispersion only twice that of the mean dispersion ofthe individual Hipparcos values. The supercluster appears not to containred giants on the first ascent of the red giant branch, but onlyasymptotic giant branch (``clump'') stars. The masses obtained forindividual components of binary stars in the supercluster show adispersion of less than 10% when compared with model predictions.
| Evolution of mass segregation in open clusters: some observational evidences
On the basis of the best available member list and duplicityinformation, we have studied the radial structure of Praesepe and of thevery young open cluster NGC 6231. We have found mass segregation amongthe cluster members and between binaries and single stars, which isexplained by the greater average mass of the multiple systems. However,the degree of mass segregation for stars between 1.5 and 2.3 M_sun isless pronounced in Praesepe than in the Pleiades. Furthermore, masssegregation is already present in the very young open cluster NGC 6231although this cluster is likely still not dynamically relaxed. Wediscuss the implications of these results and propose a qualitativescenario for the evolution of mass segregation in open clusters. InPraesepe the mass function of single stars and primaries appears to besignificantly different, like in the Pleiades. We observe an absence ofellipticity of the outer part of Praesepe. Tables 2 and 3 are availableonly in electronic form from the Strasbourg ftp server at 130.79.128.5
| Photoelectric photometry and period analysis of selected Delta Scuti stars in Praesepe
Photoelectric photometry of seven Delta Scuti stars in Praesepe wassecured. Three of them were observed simultaneously at observatorieslocated at different longitudes. Period analysis has been carried outfor each star with different computing packages and the results comparedto those in the literature. Their physical characteristics have beendetermined from the Stroemgren photometry and theoretical and empiricalcalibrations. The observations are available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.70.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Spectrophotometry of 237 Stars in 7 Open Clusters
Spectrophotometry is presented for 237 stars in 7 nearby open clusters:Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, andM39. The observations were taken by Lee McDonald and David Bursteinusing the Wampler single-channel scanner on the Crossley 0.9m telescopeat Lick Observatory from July 1973 through December 1974. Sixteenbandpasses spanning the spectral range 3500 Angstroms to 7780 Angstromswere observed for each star, with bandwidths 32Angstroms, 48 Angstromsor 64 Angstroms. Data are standardized to the Hayes-Latham system tomutual accuracy of 0.016 mag per passband. The accuracy of thespectrophotometry is assessed in three ways on a star-by-star basis.First, comparisons are made with previously published spectrophotometryfor 19 stars observed in common. Second, (B-V) colors and uvby colorsare compared for 236 stars and 221 stars, respectively. Finally,comparsions are made for 200 main sequence stars to the spectralsynthesis models of Kurucz, fixing log g = 4.0 and [Fe/H] = 0.0, andonly varying effective temperature. The accuracy of tests using uvbycolors and the Kurucz models are shown to track each other closely,yielding an accuracy estimate (1 sigma ) of 0.01 mag for the 13 colorsformed from bandpasses longward of the Balmer jump, and 0.02 mag for the3 colors formed from the three bandpasses below the Balmer jump. Incontrast, larger scatter is found relative to the previously publishedspectrophotometry of Bohm-Vitense & Johnson (16 stars in common) andGunn & Stryker (3 stars). We also show that the scatter in the fitsof the spectrophotometric colors and the uvby filter colors is areasonable way to identify the observations of which specific stars areaccurate to 1 sigma , 2 sigma , .... As such, the residuals from boththe filter color fits and the Kurucz model fits are tabulated for eachstar where it was possible to make a comparison, so users of these datacan choose stars according to the accuracy of the data that isappropriate to their needs. The very good agreement between the modelsand these data verifies the accuracy of these data, and also verifiesthe usefulness of the Kurucz models to define spectrophotometry forstars in this temperature range (>5000 K). These data define accuratespectrophotometry of bright, open cluster stars that can be used as asecondary flux calibration for CCD-based spectrophotometric surveys.
| The most resonant pulsation frequency of delta Scuti stars
Pulsation of the Sun with a period of P0 ~ 160 min discoveredabout two decades ago, is still waiting explanation. In view of thehypothesis about its cosmological origin, and attempting to findsignature of this \p\ periodicity among other (short--period variable)stars, the pulsation frequencies of \del stars are subjected to specificanalysis. With a confidence level ~ 3.8sigma it is found that thefrequency nu_ {0} be the most ``resonant'' one for the total sample of318 pulsating stars of del type (the most commensurable, or``synchronizing'', period for all these stars occurs to be 162 \pm 4min). We conjecture that a) the p \ oscillation might be connected withperiodic fluctuations of gravity field (metrics), and b) the primaryexcitation mechanism of pulsations of del stars, reflected by this``ubiquitous'' p \ resonance, must be attributed perhaps to superfastrotation of their inner cores (their rates tend to be in near--resonancewith the ``universal'' \nu0$ frequency). The arguments aregiven favouring a cosmological nature of the \p\ oscillation.
| Pulsation models of δ Scuti variables. I. The high-amplitude double-mode stars.
The relations between high-amplitude δ Scuti stars and the muchmore abundant low-amplitude δ Sct variables are not clear. Bothgroups have similar periods and seem to have almost the same basicphysical properties, although their light-curve characteristics are verydifferent. In the last few years much improved observational data havebeen published, and improved theoretical physics - in particular the newOPAL/OP opacities - now allows much more accurate calculations oftheoretical evolution models including the normal-mode pulsationfrequencies. We here use new series of stellar envelope models to givecalibrations of the first overtone-to-fundamental mode and thesecond-to-first overtone period ratios in terms of the primary modelparameters: metal content and mass-luminosity relation. Effects of thesecondary model parameters: hydrogen content, position within theinstability strip and assumed efficiency of convection are also studiedin detail, and shown to be small. These results combined with pulsationanalysis of new stellar evolution models are applied to discuss theavailable information for double-mode high-amplitude δ Sct stars.We conclude that observed period ratios and positions in the HR-diagramare in agreement with the assumption that these variables are normalstars following standard evolution. Observational data for SX Phoenicisand AI Velorum are compared with theoretical evolution sequences. It isshown that the photometry and the observed two periods of SX Pheconstrain the metal content to Z=0.001, the mass to 1.0 solar masses andthe bolometric magnitude to about 2.70mag. The inferred distance of SXPhe gives a parallax of 0.012+/-0.002arcsec compared with that of theHIPPARCOS Input Catalogue of 0.023+/-0.008arcsec. For AI Vel theavailable photometry and the two primary observed periods do not providea unique solution. Models based on OPAL opacities allow Z=0.01-0.02 withcorresponding masses 1.6-2.0 solar masses. This can be understood by thecompensating effects from Z and the mass-luminosity relation in thecalibration of the period ratio. It is suggested that the surprisinglynarrow interval in the first overtone-to-fundamental mode period ratioobserved in the double-mode δ Sct stars may be due to thesecompensating effects. Attempting to fit low-amplitude modes observed inAI Vel in addition to the primary oscillations, it is concluded that thepresent models cannot explain these oscillations in terms of radialmodes. The little understood relations between high- and low-amplitudeδ Sct stars are briefly discussed, and the problem of modeidentification is emphasized.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| High-precision study of proper motions and membership of 924 stars in the central region of Praesepe.
High-precision proper motions for 257 and 296 stars in a 90'x90' regioncentered on BD+20 2170 were obtained from seven plates taken with the40cm refractor (f=6895mm) at Zo-Se station of Shanghai Observatory withsix AC plates and the stellar positions in Russell's (1976) catalogue,respectively. Combining with the data given by Klein-Wassink (1927),Jones (1971), Artyukhina (1971), and Jones & Cudworth (1983), theseproper motions give a sample of 924 stars in the region mentioned above.With membership probabilities estimated by an improved maximumlikelihood method, a very good sample of 198 members is obtained withproper motion accuracies ranging from +/-0.2 to +/-5.0mas/yr, of which60 per cent are better than +/-1.0mas/yr, and the completeness nearlydown to B=15.5.
| Pulsation in moderate rotating delta Scuti stars: The case of BN and BU CANCRI
The results reported in this paper concern two delta Scuties in thePraesepe cluster, namely BN Cnc and BU Cnc, observed during the 1992STEPHI 4 campaign. Five and six frequency peaks, respectively, wererecorded as a result of the campaign. In this work, an attempt is madeto identify these frequency peaks as pulsation models, based on stellarstructure and oscillation computations. Rotation effects in thefrequencies are considered up to second order. Since both stars belongto the same cluster, more severe constraints than for isolated stars canbe imposed. Evidence is found to support the presence of mixed modessplit by rotation. The frequencies of such modes strongly depend on theinput physics to the models and can hence become an important test forthe stellar structure theory.
| A catalogue of variable stars in the lower instability strip.
Identifications, positions, photometry, spectra, some pulsationalfeatures, other astrophysical parameters and literature for 302pulsating variable stars in the lower instability strip, near the ZAMS,are given. About 185 stars have near homogeneous photometric informationin the Stroemgren's uvby-β photometric system. Thiscatalogue/database covers information published until November 1993.
| Main Sequence Variables
The pulsators along and near the main sequence are well-suited forasteroseismology and provide a probe of the stellar interior and itschanges with evolution. With the exception of rapidly oscillating Apstars (roAp), the pulsation periods range from 0.5 h to days. Thisrequires multisite campaigns lasting several weeks. The delta Scuti,roAp and beta Cephei variables offer the greatest potential, while thelonger-period g-mode pulsators (SPB -- slowly pulsating B stars -- andgamma Doradus variables) are very difficult to study. A summary of themultiperiod structure of delta Scuti stars is given. The twobest-studied stars, FG Vir and CD--24(deg) 7599, both have been WETtargets. A preliminary analysis of the 1995 campaign of FG Vir hasalready detected 19 frequencies. The standard photometric WET techniquehas a high duty cycle since the variable star is observed continuouslywith one channel. The study of main sequence variables requiresphotometric stability at low frequencies. The extension of the WETtechnique to low frequencies and its modification are discussed.
| Is Praesepe KW284 Actually a delta Scuti Star?
Not Available
| Multi-period pulsation of the delta Scuti star 63 Herculis
Multisite photoelectric B and V photometry of the delta Scuti star 63Her was obtained on three continents. Three frequencies of pulsation(f1 = 11.32, f2 = 20.07 and f3 = 7.72c/d) were detected with a signal/noise amplitude ratio greater than or =4.0. The three frequencies fit all the available data ranging back to1968. Reports in the literature of discepant behavior of the 1968measurements were probably caused by overinterpretation. The newfrequency values are in excellant agreement with the results found byReed & Welch from their 1983 data, except for a 1 c/d alias in theirvalue for f2. Two additional pulsation frequencies in thelow-frequency g-mode domain with amplitudes near two millimag reportedby the STEPHI group are not seen in the new campaign data. The new datashow average noise levels just below one millimag in this frequencydomain, so that the existence of these two frequencies cannot bedisproved from the new data alone. However, a reanalysis of the STEPHIdata also suggests that these frequencies might not be real. The resultsfrom the two multisite campaigns should be free of 1 c/d aliasing, sothat a resonance hypothesis involving f2 = f1 +f3 can be rejected. The value of the pulsation constantassociated with f3, Q = 0.046 +/- 0.008 d, is too high by 2standard deviations to be explained by radial pulsation. The Q value isincompatible with those of nonradial p1 to p4modes commonly found in delta Scuti stars.
| δ Scuti stars: a new revised list
An extensive and up to date list of δ Sct stars is presented. Thiscatalogue is intended to be a comprehensive review of observationalcharacteristics of all the δ Sct stars known until now, includingstars contained in earlier catalogues together with other new discoveredvariables, covering information published until November 1993. Globalinformation in the form of histograms and diagrams are also shown.
| Post-main-sequence and POST red giant branch variables with pulsation periods less than one day
Post-main-sequence (mass 1 to 3 solar masses) and post-giant branch (0.5to 1 solar mass) pulsators are discussed on the basis of four color andH beta light curves published elsewhere. The post-main-sequencevariables, called ultrashort period cepheid (USPC) (delta Sct), pulsatein the fundamental and first harmonic modes of radial pulsation and, inmany cases, in nonradial modes. The variables for which photometryallows accurate, luminosity estimates and are known to pulsatesimultaneously in the fundamental and first harmonic or in thefundamental mode alone, define a PL relation (MV = -2.80 logP - 0.60, fundamental). It is notable that the slope of this relation isin the range of slopes found for classical cepheids. Accurate Vphotometry is lacking for many of the variables known as 'anomalouscepheids', but the available data divide them into low mass,pseudocepheids (BL Her and W Vir stars) and post-main-sequence USPC(delta Sct) variables. Four USPC in NGC 5053 and six in NGC 6466, forwhich accurate photometry is available, give remarkably consistentmoduli of 16.06 +/- 0.05 and 15.98 +/- 0.08 mag, respectively, for theclusters, in which they are blue stragglers similar to SX Phe inKapteyn's star group. The assumption that the four post-giant branchvariables, called VSPC (RR Lyr), S Ari, SU Dra, and ST Leo in Kapteyn'sstar group and RR Lyr in the Groombridge 1830 group, are physicalmembers of these groups and share their V-velocities, leads to acalibration of the photometry for the derivation of reddening,luminosity, and heavy element abundance of 45 field variables. Theresulting reddenings are consistent with values obtained by othermethods and the metallicities are consistent with the most accuratelyavailable spectroscopic determinations of delta S and of Ca II K. Theluminosities of the bulk of the variables confirm Sandage's (1993)relation between MV and (Fe/H). Four or five of the fieldvariables are probably binary, including BB Vir which Kinman &Carreta (1992) have independently noted as double. The PL relation forUSPC (delta Sct) variables intersects the horizontal branch (HB) near P= 0.3d and at least two field very short period cepheid (VSPC) (RR Lyr)star, FW Lup (0.484 d) and ST Pic (0.486 d) may be first overtonepulsators of the USPC (delta Sct) variety. A dozen field VSPC (RR Lyr)stars populate a (Fe/H), MV relation with the same slope asthe other stars but displaced 0.7 mag toward higher luminosities. Theonly cluster variable found to populate this diplaced relation is No. 9in 47 Tuc, although ST Vir, which may be a member of the Arcturus group,should also be considered. The elevated luminosities are unlikely to becaused by either evolution or errors in the photometric indices. Apossible source of these apparently young VSPC(RR Lyr) variables withhalo metallicity is in second (or third) generation globular clustersformed during an episodic collapse of the galaxy that produced metalpoor stars but in a dynamical situation that hastened the disruption ofthe clusters, currently formed, before the still older globularclusters, created under conditions that have kept them in a moredisruptive free environment.
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Наблюдательные данные и астрометрия
| Созвездие: | Рак |
| Прямое восхождение: | 08h39m44.67s |
| Склонение: | +19°16'30.8" |
| Видимая звёздная величина: | 7.636 |
| Собственное движение RA: | -34.7 |
| Собственное движение Dec: | -12.9 |
| B-T magnitude: | 7.87 |
| V-T magnitude: | 7.656 |
Каталоги и обозначения:
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