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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.
| δ Sct-type pulsations in eclipsing binary systems: RZ Cas
We present the results of a three-continent multisite photometriccampaign carried out on the Algol-type eclipsing binary system RZ Cas,in which the primary component has recently been discovered to be aδ Sct-type pulsator. The present observations include, for thefirst time, complete simultaneous Strömgren uvby light curvestogether with a few Crawford Hβ data collected around the orbitalphase of the first quadrature. The new observations confirm thepulsational behaviour of the primary component. A detailed photometricanalysis, based on these observations, is presented for both binarityand pulsation. The results indicate a semidetached system where thesecondary fills its Roche lobe. The appearance of the light curvesreveals the presence of the mass stream from the secondary component anda hotspot where this stream impacts on the surface of the primary star.There are also some indications of chromospheric activity in thesecondary. On the other hand, the pulsational behaviour out-of-primaryeclipse can be well described with only one frequency at 64.1935cd-1 similar to the main peak found by Ohshima et al. Theexistence of multiperiodicity is not confirmed in our data. Concerningthe mode identification, our results indicate non-radial pulsation in ahigh radial order (n= 6), with l= 2, |m|= 1, 2 as the most suitable.However, additional effects must be taken into account in thepredictions. Moreover, the pulsation amplitude in the u band is largerthan in b and v, which is unusual among the δ Sct-type variables.This can be explained as due to pulsation in a high n value and close tothe blue edge of the δ Sct region. On the other hand, the earlydata of Ohshima et al. have also been analysed and similar results arefound concerning the frequency content and pulsational amplitude.Finally, a revision of all the photometric out-of-primary-eclipse datasets available in the literature is made together with some additionalunpublished data leading to interesting findings relative to changestaking place in the pulsation amplitudes and frequencies from season toseason. Furthermore, multiperiodicity is probably present in someepochs.
| 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.
| The Evolution of Cool Algols
We apply a model of dynamo-driven mass loss, magnetic braking, and tidalfriction to the evolution of stars with cool convective envelopes; inparticular, we apply it to binary stars where the combination ofmagnetic braking and tidal friction can cause angular momentum loss fromthe orbit. For the present we consider the simplification that only onecomponent of a binary is subject to these nonconservative effects, butwe emphasize the need in some circumstances to permit such effects inboth components.The model is applied to examples of (1) the Sun, (2) BYDra binaries, (3) Am binaries, (4) RS CVn binaries, (5) Algols, and (6)post-Algols. A number of problems regarding some of these systems appearto find a natural explanation in our model. There are indications fromother systems that some coefficients in our model may vary by a factorof 2 or so from system to system; this may be a result of the chaoticnature of dynamo activity.
| 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.
| Low-frequency variability and binarity of the δ Scuti star XX Pyx
We analyse 147h of single-site CCD time series photometry of themultiperiodic low-amplitude δ Scuti star XX Pyx with the aim ofinvestigating variability at low frequencies. Part of the data wereobtained in the context of the 1998 multisite campaign on XX Pyx, theresults of which were described by Handler et al. We find that periodiclow-frequency variations are present in the XX Pyx light curves, and wedetect two frequencies at fA=0.8695cycled-1 andfB=1.7352cycled-1, respectively, with amplitudesof 4.5 and 5.4mmag. The low-frequency variability is intrinsic to XXPyx, and cannot be attributed to instrumental or atmospheric effects.The near 2:1 ratio of the frequencies leads us to suggest that XX Pyx isa δ Scuti star in a binary system, with a possible binary periodof 27.6h. This is strongly supported by the detection of radial velocityvariations from the re-analysis of echelle spectra obtained by Handleret al. However, in the absence of a spectroscopic period, alternativeexplanations of the photometric variability involving pulsation are alsopossible; the variations occur close to possible combination frequenciesof the short-period (δ Scuti) variations, but high Q values of0.57 and 0.28d suggest that the variations are not a result of normal(p-)modes. They could possibly be due to g-modes excited to observableamplitudes as a result of resonance effects. Surface features (spots)are unlikely to be the cause of the variations. We searched forcombination frequencies (fi-fj), f being thenormal δ Scuti frequencies detected by Handler et al., but failedto detect any.
| Pulsation in the pre-main-sequence Herbig Ae star HD 142666
Asteroseismology of pre-main-sequence δ Scuti stars has thepotential not only to provide unprecedented constraints on models ofthese stars, but also to allow for the possibility of detectingevolutionary period changes, thus providing a direct measure of thepre-main-sequence evolutionary time-scale. In the last two years, thepublished number of such stars known has doubled from four to eight.Searches are now being conducted amongst the Herbig Ae stars, which areconsidered to be excellent candidates. We announce the discovery ofδ Scuti pulsation in one Herbig Ae star, HD 142666, which lieswithin Marconi & Palla's theoretically predicted instability stripfor pre-main-sequence stars, making this the ninth knownpre-main-sequence δ Scuti star. We also demonstrate a lack ofδ Scuti pulsation in another such star, HD 142527.
| Simultaneous uvby photometry of the delta Sct star HD 129231
We present the results of a three-year Strömgren uvby photometricstudy of the recently discovered multiperiodic low amplitude deltaSct-type pulsator HD 129231. Some additional Hbeta -Crawfordmeasurements were also collected. Multiperiodicity is needed to describethe pulsational behaviour of this variable during each of the observingruns. A set of five significant frequencies has been found as the bestfitting for the 1997 dataset, but only the two main ones result assignificant during the 1995 and 1996 observing runs. Amplitudevariations from season to season are also found for the main frequencyf_1. Nonradial pulsation is suggested for some of the modes. Using thederived uvbybeta indices, the most relevant physical parameters of HD129231 are also determined placing this object as a hot Population Idelta Sct star evolving on its main sequence stage.
| 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).
| Asteroseismology of the Multiply Periodic δ Scuti Star θ Tucanae
We present an asteroseismological analysis of the δ Scuticomponent of the binary star system θ Tucanae, using the 10pulsational frequencies obtained photometrically by Paparó et al.and the mode identifications of Sterken. We have tested theoreticalmodels with masses between 1.8 and 2.8 Msolar that have solarmetal abundances, and we find that based upon mode stability arguments,the photometrically derived mass estimate of 2.1+/-0.1 Msolaris probably accurate. The models with the best frequency match toθ Tucanae have masses of 1.9-2.1 Msolar, luminositiesbetween 20 and 25 Lsolar, effective temperatures between 7500and 7685 K, logg values between 3.82 and 3.92, and rotational velocitiesbetween 70 and 90 km s-1. The luminosities of our models aremore than a factor of 2 less than the Hipparcos-derived luminosity of 54Lsolar, which suggests that the secondary star must be ofcomparable luminosity. We cannot determine whether tidal distortion iscausing nonspherical perturbations in the pulsating component of thissystem with our current models, but the frequency spacing of observedpulsation modes suggests that rotation has a strong effect on theobserved spectrum. Our models are consistent with the observed pulsationspectrum if rotational splitting is taken into account. Recently, DeMey, Daems, & Sterken determined spectroscopically that the θTucanae system is a spectroscopic binary with an anomalous mass ratio of0.0896. In their model of this system, the δ Scuti component ofthe system is probably the beneficiary of mass transfer from thesecondary, and the system was likely once an Algol-type system. Thesecondary is probably a 0.2 Msolar post-red giant branchobject at ~7000 K (logg~3.0), which has lost most of its mass via masstransfer and winds. This scenario raises the possibility that theinterior of the δ Scuti star may be radically different from whatsingle-star evolution models predict, although our results do not showany obvious differences. However, the age and envelope abundances shouldbe different from single-star model predictions. We believe that thisobject provides an excellent opportunity to study the interiors ofpost-mass transfer objects using asteroseismology, and we suggest futureobservational and theoretical work that will help us understand thissystem.
| 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
| The delta Scuti star theta Tucanae. III. Observational guidelines for mode identification
On the basis of almost 2000 b, y photoelectric observations of thetaTucanae collected in an international campaign at two sites and ofalmost 1500 v, u observations collected at one site, observationalguidelines for mode identification have been searched. Not only thegenerally used plane (Ab-y/Ay versus phib-y - phiy ) but each combination of thenonadiabatic observables including amplitude ratio vs. amplitude ratioand phase difference vs. phase difference planes were checked forguidelines. Especially Ab/Ay amplitude ratio andphi b-y - phib phase difference proved to beuseful criteria for mode separation in the case of theta Tucanae. The 10pulsational frequency values published previously by Paparó etal. (\cite{pap96}) are distributed in three groups according toAb/Ay and in two distinct levels according to phib-y - phib . The groups consist of closely spacedfrequencies. Group III (15.86, 15.94 and 17.06 cycles/day) displays ahigher, distinct level than the others according to theAb-y/Ay amplitude ratio and unusual behaviour in ucolour. Although the discriminative plane does not give the exact valueof quantum numbers but predicts which theoretical modes must share thesame behaviour. Calibration of the pure observational guidelines by new,delicate theoretical calculation for planes of nonadiabatic observablesconcerning the location of theoretical modes is urged. Based onobservations obtained at the South African Astronomical Observatory,Sutherland, South Africa and at the European Southern Observatory, LaSilla, Chile (Program 51 - 7 - 038).
| Mode and period changes in pulsating stars near the main sequence : delta Scuti stars.
Not Available
| An improved method for the determination of the orbital parameters of a binary system that contains a pulsating component
In this paper we present a method to assign statistical weights toradial-velocity measurements of a binary system of which one of thecomponents is a variable star. The basic idea of the method is toseparate the radial-velocity changes due to the intrinsic variabilityfrom those due to the orbital motion. This can be achieved if part ofthe data set consists of good coverages of the intrinsic variabilitycycle. These full coverages are used to estimate the variability for thenights on which only one or a few spectra were obtained. Our techniqueis applicable when the intrinsic variability has a period that isconsiderably shorter than the orbital period. Once weights have beenassigned, existing methods to derive the orbital parameters can be usedwith better accuracy compared to the case where all data points aretreated as if no intrinsic variability were present (equal weights). Weillustrate our method and compare the orbital solution obtained with andwithout assigning weights for three pulsating stars in a binary system:beta Cru, varepsilon Per, and kappa Sco.
| XCOV13 and Asteroseismology of Delta Scuti Stars
The Whole Earth Telescope XCOV13 campaign, which was carried out from atemporary command center in Vienna, included two main-sequencepulsators: the delta Scuti star 4 CVn and the new gamma Dor variable, HD108100. The astronomical results for these stars are summarized. Thepaper also discusses the progress as well as further potential of deltaScuti stars for asteroseismology. Extensive multi-site campaigns ofindividual delta Scuti stars show that 24 or more pulsation modes with lvalues of 0, 1 and 2 can be detected photometrically. Spectroscopically,also about 30 modes have been detected, and these can be identified withmodes of l values up to 20. Since each technique favors the detection ofspecific types of modes, hundreds or thousands of modes must be excitedin delta Scuti stars. We examine the quantities which can be matchedbetween observations and theoretical models specifically computed foreach star. Recent progress in the mode identification of multiplepulsation modes is illustrated by presenting an application of the phaseshift method for the two stars, FG Vir and 4 CVn, recently measured byDSN (Delta Scuti Network) and WET. The XCOV13 results on 4 CVn can beused to illustrate why less extensive studies of delta Scuti could leadto erroneous conclusions of unstable pulsation modes.
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Theta Tucanae: a binary with a delta Scuti primary
Using seven four-hour time series of high-resolution spectra, the binarynature and the oscillations of theta Tuc are investigated. The spectrumis double-lined, proving the binarity. theta Tuc is a binary with acircular orbit and with an anomalous mass ratio q=0.09. The for thefirst time determined orbital elements are P=7.1036 days,K1=8.6 km/s and K2=95.6 km/s. The oscillations ofthe delta Scuti-type main component are spectroscopically investigated.Line-profile variations are discovered, and radial-velocity variationsreveal a main oscillation frequency of f1=20.27 c/d whichcorresponds to the main oscillation 20.2806 c/d in photometry. Anotherfrequency, f2=18.82 c/d found in the spectroscopic data andnot present in the photometric dataset, needs to be investigated moreprofoundly. Based on observations collected at the European SouthernObservatory, La Silla, Chile. (Observing proposals 57 E-0269 and 58D-0150)
| Convection, Thermal Bifurcation, and the Colors of A Stars
Broadband ultraviolet photometry from the TD-1 satellite andlow-dispersion spectra from the short wavelength camera of IUE have beenused to investigate a long-standing proposal of Bohm-Vitense that thenormal main-sequence A and early-F stars may divide into two differenttemperature sequences: (1) a high-temperature branch (and plateau)comprised of slowly rotating convective stars, and (2) a low-temperaturebranch populated by rapidly rotating radiative stars. We find noevidence from either data set to support such a claim, or to confirm theexistence of an "A-star gap" in the B-V color range 0.22 <= B-V <=0.28 due to the sudden onset of convection. We do observe, nonetheless,a large scatter in the 1800--2000 A colors of the A--F stars, whichamounts to ~0.65 mag at a given B-V color index. The scatter is notcaused by interstellar or circumstellar reddening. A convincing case canalso be made against binarity and intrinsic variability due topulsations of delta Sct origin. We find no correlation with establishedchromospheric and coronal proxies of convection, and thus nodemonstrable link to the possible onset of convection among the A--Fstars. The scatter is not instrumental. Approximately 0.4 mag of thescatter is shown to arise from individual differences in surface gravityas well as a moderate spread (factor of ~3) in heavy metal abundance andUV line blanketing. A dispersion of ~0.25 mag remains, which has noclear and obvious explanation. The most likely cause, we believe, is aresidual imprecision in our correction for the spread in metalabundances. However, the existing data do not rule out possiblecontributions from intrinsic stellar variability or from differential UVline blanketing effects owing to a dispersion in microturbulentvelocity.
| Luminosity and related parameters of δ Scuti stars from HIPPARCOS parallaxes. General properties of luminosity.
The absolute magnitudes of δ Scuti stars derived from parallaxesmeasured by the Hipparcos astrometric satellite are discussed andcompared with the previous estimates based on photometric uvbyβindices. There are significant differences which are related tophotometric effects of metallicity and rotational velocity, but thepossible effect of a close companion on the measured apparent magnitudeshould be also taken into account. The possibility of differentgroupings of δ Scuti stars based on the absolute magnitudes isbriefly discussed. Some high amplitude δ Scuti stars withintermediate or normal metallicity and small and uncertain parallax haveapparently a very low luminosity; this could be a systematic effectrelated to the observational errors.
| The δ Scuti star θ Tucanae. II. UVBY colour variations and pulsational/orbital properties.
On the basis of almost 1500 uvby photometric observations of θTucanae collected in 1993, we discuss the colour variation of thismulti-periodic δ Scuti star and debate some of its binary andpulsational properties. The frequencies f_1_=0.281 and f_2_=0.142c/dembody orbital motion in a 7.04d day ellipsoidal configurationcharacterised by a light curve with unequal maxima and minima and acolour index that becomes bluer during the minimum phases. The firstresults of an analysis of the light curve points towards a mass ratio qof the order of 0.10-0.15. We present dependable numerical values forcolour phase differences and amplitude ratios A_b-y_/A_y_,φ_b-y_-φ_y_, A_v-y_/A_y_, φ_v-y_-φ_y_ andA_u-y_/A_y_, φ_u-y_-φ_y_ which can be used for pulsation-modeidentification. The principal pulsation frequency f_7_=20.28c/d isreconcilable with a radial mode.
| Complex behaviour of the δ Scuti star θ Tucanae. I. Frequencies in the light variation.
On the basis of more than 2300 new Stroemgren y and Johnson Vphotometric observations collected during 246 hours spread over 42nights at three sites in 1993, we present a frequency analysis of thelight variation of θ Tuc. 10 frequencies were found in the rangeof 15.8 to 20.28cycles/day displaying an extreme regularity. Frequenciesare situated in groups and these groups are equally spaced. Some kind ofsplitting is definitely involved. The frequencies are constant inamplitude on a short time scale. Two frequencies, 0.282 and0.142cycles/day (3.56 and 7.04days period) were found to be responsiblefor the mean light level variation of θ Tuc. Although θTuc is known as a single star, the length and shape of the mean lightlevel variation and the unusual behaviour of θ Tuc in ultravioletand infrared suggest that the δ Scuti star θ Tuc is aprimary in a binary system with a late F type companion.
| γ Doradus and δ Scuti stars: cousins or twins?
γ Doradus stars are a group of slowly pulsating early F dwarfswith typical low frequencies near 1c/d. The pulsation modes are probablyg modes. These stars are slightly cooler than the typical δ Scutivariables, which pulsate with higher frequencies of typically 10c/d(mostly nonradial p modes). This paper examines the relationship betweenthe two groups of variables. Additional low-frequency variability hasbeen reported for fewer than 10% of the 300 δ Scuti starsexamined. In at least one case (1 Mon), the observational data areconsistent with an alternate interpretation in terms of a modeinteraction, f_1_-f_2_, between two p modes of higher frequency, ratherthan by the excitation of g modes. In several other stars (e.g. 4 CVn),the reported low-frequency variability may originate in the comparisonstar used. Arguments are given that for a number of stars the observedlow-frequency variations are caused by observational errors (such asinstrumental drift and transparency variations). A few δ Scutistars remain for which intrinsic γ Doradus-type variability mayalready have been discovered, although no case is well-studied. One ofthe best candidates is the star BI CMi, which is situated in the smallregion of overlap of the two groups of pulsators in theHertzsprung-Russell diagram. The star deserves further study.
| Photoelectric Observations of \theta Tucanae and AB Doradus
Not Available
| A catalog of far-ultraviolet point sources detected with the fast FAUST Telescope on ATLAS-1
We list the photometric measurements of point sources made by the FarUltraviolet Space Telescope (FAUST) when it flew on the ATLAS-1 spaceshuttle mission. The list contains 4698 Galactic and extragalacticobjects detected in 22 wide-field images of the sky. At the locationssurveyed, this catalog reaches a limiting magnitude approximately afactor of 10 fainter than the previous UV all-sky survey, TDl. Thecatalog limit is approximately 1 x 10-14 ergs A sq cm/s,although it is not complete to this level. We list for each object theposition, FUV flux, the error in flux, and where possible anidentification from catalogs of nearby stars and galaxies. Thesecatalogs include the Michigan HD (MHD) and HD, SAO, the HIPPARCOS InputCatalog, the Position and Proper Motion Catalog, the TD1 Catalog, theMcCook and Sion Catalog of white dwarfs, and the RC3 Catalog ofGalaxies. We identify 2239 FAUST sources with objects in the stellarcatalogs and 172 with galaxies in the RC3 catalog. We estimate thenumber of sources with incorrect identifications to be less than 2%.
| Blue Stragglers in the Solar Vicinity: Newborn or Reborn
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110..823E&db_key=AST
| 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.
| 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.
| 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.
| A catalog of stellar Lyman-alpha fluxes
We present a catalog of stellar Ly-alpha emission fluxes, based on newand archival images obtained with the IUE spacecraft. The catalogincludes 227 stars with detectable Ly-alpha emission fluxes, and upperlimits on the Ly-alpha emission flux for another 48 stars. Multiple fluxmeasurements are given for 52 stars. We present a model for correctingthe observed Ly-alpha flux for attenuation by the local interstellarmedium, and we apply this model to derive intrinsic Ly-alpha fluxes for149 catalog stars which are located in low H I column density directionsof the local interstellar medium. In our catalog, there are 14 late-Aand early-F stars at B-V = 0.29 or less that show detectable emission atLy-alpha. We find a linear correlation between the intrinsic Ly-alphaflux and C II 1335 A flux for stars with B-V greater than 0.60, but theA and F stars deviate from this relation in the sense that theirLy-alpha flux is too low. We also find a good correlation betweenLy-alpha strength and coronal X-ray emission. This correlation holdsover most of the H-R diagram, even for the F stars, where an X-raydeficit has previously been found relative to the transition regionlines of C II and C IV.
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Osservazione e dati astrometrici
| Costellazione: | Tucano |
| Ascensione retta: | 00h33m23.30s |
| Declinazione: | -71°15'58.0" |
| Magnitudine apparente: | 6.13 |
| Distanza: | 150.376 parsec |
| Moto proprio RA: | 73.9 |
| Moto proprio Dec: | -12.5 |
| B-T magnitude: | 6.415 |
| V-T magnitude: | 6.141 |
Cataloghi e designazioni:
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