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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.
| Amplitude ratios as mode characterizors in delta Scuti stars .
Seismology of delta Scuti star s holds great potential for testingtheories of stellar structure and evolution. The ratio of modeamplitudes in light and in equivalent width of spectral lines can beused for mode identification. However, the amplitude ratios (AR)predicted from theory are usually inconsistent with observations. Wehere present the first results from a campaign aimed at calibratingobservationally the absolute values of the AR.
| 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.
| The rapidly rotating delta Scuti star AV Cetei
We present results from an international spectroscopic and photometriccampaign on the delta Scuti star AV Cet. The starhas a rich and complex pulsation spectrum, and we find 7 individualfrequencies, with evidence for many more present below our detectionlimit. We investigate the prospects for mode identification in fastrotators, using several different techniques. We compare the methods andconclude that although no single technique can give unambiguous modeidentification, the collective evidence does allow some conclusions tobe drawn, suggesting the presence of one radial mode at 14.598d-1. During the campaign we found the star HD9139 to be a variable. From our photometry we find evidencefor a variability time scale around 1 day, but we cannot find anunambiguous interpretation for its light variations.Based partly on observations made with the Danish 1.5 m telescope atESO, La Silla, Chile.
| 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 Search for Small Kuiper Belt Objects by Stellar Occultations
We report the conditions and results of an observation campaignorganized in 2000 September at the Pic du Midi Observatory, anddedicated for the first time to the study of Kuiper belt objects (KBOs)by stellar occultations. The observation consisted of recording the fluxof a well-chosen star with a fast photometer (20 Hz) and countingoccultations of this star by passing KBOs. The campaign provided 15 hrof good-quality signal (rms σ~1.8%) and zero detections of KBOs ata 4 σ detection level. For a KBO differential size distributionassumed to vary as r-q, this first result suggests a slopeq<~4.5. A refined analysis of the data, studying diffractionpatterns, allowed us to find an event at a 3 σ detection levelcompatible with a 150 m KBO. More generally, observation campaigns ofstellar occultation by KBOs on >=2 m class telescopes couldstatistically constrain the slope and the expected turnover radius dueto collisional erosion of the subkilometer KBO size distribution.
| Time-series spectroscopy of pulsating sdB stars - III. Line indices of PG 1605+072
We present the detection and analysis of line index variations in thepulsating sdB star PG 1605+072. We have found a strong dependence ofline index amplitude on Balmer line order, with high-order Balmer lineamplitudes up to 10 times larger than Hβ. Using a simple model, wehave found that the line index may not only be dependent on temperature,as is usually assumed for oscillating stars, but also on surfacegravity. This information will provide another set of observables thatcan be used for mode identification of sdBs.
| 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.
| Mode characterisation in delta Scuti stars. I. rho Pup, GN And, V1208 Aql and AV Cet
We present new spectroscopic observations of four bright delta Scutipulsators. Line indices of the Balmer lines can be used to establishmode identifications using the ratio R between such line indexamplitudes and photometric amplitudes. For the well known radialpulsator rho Pup an absolute value of the amplituderatio of the radial mode was found to R=0.43, consistent with earliervalues of R ~ 0.5 reported for other delta Scuti stars. In GNAnd we recover the recently reported newly excited mode, whilethe former dominant mode was not recovered. We confirm thatV1208 Aql is a non-radial pulsator, containing twomodes of different degree. In V1208 Aql we report a previously unseenmode behavior: the phases of both modes are reversed between the coreand wings of the Hβ line, suggesting the presence of moreundetected modes. For AV Cet we find that thedominant mode is a previously undetected one. We suggest the undertakingof new photometric observations of rho Pup, GN And, V1208 Aql and AV Cetto determine the frequencies and amplitudes of the pulsations. Based inpart on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile.
| delta Scuti stars in Praesepe. II. The STACC 1998 campaign - The spectroscopy
We present the results of a large international spectroscopic campaignon the delta Scuti star BN Cnc. Combiningobservations from five observatories taken over more than two weeks, wecalculate line indices of the Hα line. A line index is theintegrated line flux in a software filter divided by the continuum flux.We demonstrate that this can be used in combination with simultaneousphotometry to classify the oscillation modes. We recover all thefrequencies also found from photometry and assign likely modeidentifications, which differ slightly from previously published values,but are found to be consistent with simple models. The difference inidentification is found to have very little effect on the derivedluminosity and temperature.
| 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
| 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
| 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
| The search for delta Scuti stars in open clusters
In order to improve the tests of models of stellar evolution,observations giving tighter constraints on the models were initiated bythe formation of an informal group STACC (Frandsen, 1992). The purposeof the group is to search for and make observations of delta Scuti starsin open clusters. This paper presents some of the results of the search,mainly for distant open clusters with a rich population of variables.Included is an announcement of a target list (Frandsen & Arentoft1998, The Book) and four examples of new Colour-Magnitude (CM) diagramsof open clusters considered to be interesting targets. Finally, wepresent the fruits of extensive searching: an open cluster that containsmany delta Scuti stars. Based on observations made at the EuropeanSouthern Observatory, La Silla, the Nordic Optical Telescope, ORM, LaPalma and the IAC80, OT, Tenerife
| 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
| 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.
| A ROSAT X-ray study of the Praesepe cluster.
We present the results of ROSAT PSPC observations of the Praesepecluster. 68 Praesepe candidates have been detected, above a threshold of=~2x10^28^erg/s, in the ~4x4deg area of the cluster covered by theobservations. 56 out of the 68 detected objects are cataloged as highprobability Praesepe members. Praesepe members of all spectral typeshave been detected with X-ray luminosities ranging from the sensitivitylimit to approximately 10^30^erg/s in the ROSAT broad band. The highestX-ray luminosity has been measured for a very short period W UMa typeSB2 binary. 2 out of the 4 Praesepe late-type giants have also beendetected. X-ray luminosity distribution functions have been derived forlate-type stars in the sample, taking into account both detections andupper limits. The main and most surprising finding are the low detectionrates derived for Praesepe low mass dwarfs. We detected about 30% of theF and G stars, and the detection rate among K and M dwarfs is evenlower. Correspondingly, the luminosity distribution functions for starsin selected color intervals are dominated by the contribution of upperlimits, with the medians below the sensitivity threshold. The comparisonwith the Hyades all-sky survey results shows an evident discrepancybetween the average X-ray properties of late-type dwarfs in the twoapparently coeval clusters; such a discrepancy must be an intrinsic one,since the observations are characterized by similar sensitivities.
| 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.
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Observation and Astrometry data
| Constellation: | Cancer |
| Right ascension: | 08h40m39.24s |
| Declination: | +19°13'41.9" |
| Apparent magnitude: | 7.766 |
| Proper motion RA: | -35.5 |
| Proper motion Dec: | -12.4 |
| B-T magnitude: | 8.039 |
| V-T magnitude: | 7.789 |
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