Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Time-dependent convection seismic study of δ Sct stars
We apply for the first time the time-dependent convection (TDC)treatment of Gabriel and Grigahcène et al. to the modeidentification and seismic study of δ Sct stars. We consider theinfluence of this treatment on the photometric amplitude ratios andphase differences, and compare our TDC results to frozen convection (FC)results. We also compare the results obtained with different values ofthe mixing-length (ML) parameter α. Finally, we identify the modesand perform a seismic study of the stars V784 Cassiopeae (Cas), 1Monocerotis (Mon) and 28 Andromedae (And), and show that our TDC modelsagree better with observations than FC models.
| The chemical composition of δ Scuti*
We present chemical abundances in the photosphere of δ Scuti(δ Sct) - a prototype of the class of pulsating variables -determined from the analysis of a spectrum obtained by using the 2-mtelescope at the Peak Terskol Observatory and a high-resolutionspectrometer with R= 52000, a signal-to-noise ratio 250 and fromInternational Ultraviolet Explorer spectra. The abundance pattern ofδ Sct consists of 49 chemical elements. The abundances of 19elements have not been investigated previously. The abundances of Pr andNd obtained from the lines of the second and third spectra are equal.The abundances of heavy elements indicate the overabundances withrespect to the solar system values up to 1 dex. The abundance pattern ofδ Sct is similar to the abundance patterns of Am-Fm or δ Deltype stars.A splitting of the cores of all clean lines is observed for the spectraof δ Sct and HD 57749. This can signify evidence of non-radialpulsations in these stars.
| The physical properties of normal A stars
Designating a star as of A-type is a result of spectral classification.After separating the peculiar stars from those deemed to be normal usingthe results of a century of stellar astrophysical wisdom, I define thephysical properties of the "normal" stars. The hotter A stars haveatmospheres almost in radiative equilibrium. In the A stars convectivemotions can be found which increase in strength as the temperaturedecreases.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| Automated spectroscopic abundances of A and F-type stars using echelle spectrographs. II. Abundances of 140 A-F stars from ELODIE
Using the method presented in Erspamer & North (\cite{erspamer},hereafter Paper I), detailed abundances of 140 stars are presented. Theuncertainties characteristic of this method are presented and discussed.In particular, we show that for a S/N ratio higher than 200, the methodis applicable to stars with a rotational velocity as high as 200 kms-1. There is no correlation between abundances and Vsin i,except a spurious one for Sr, Sc and Na which we explain by the smallnumber of lines of these elements combined with a locally biasedcontinuum. Metallic giants (Hauck \cite{hauck}) show larger abundancesthan normal giants for at least 8 elements: Al, Ca, Ti, Cr, Mn, Fe, Niand Ba. The anticorrelation for Na, Mg, Si, Ca, Fe and Ni with Vsin isuggested by Varenne & Monier (\cite{varenne99}) is not confirmed.The predictions of the Montréal models (e.g. Richard et al.\cite{richard01}) are not fulfilled in general. However, a correlationbetween left [(Fe)/(H)right ] and log g is found for stars of 1.8 to 2.0M_sun. Various possible causes are discussed, but the physical realityof this correlation seems inescapable.Based on observations collected at the 1.93 m telescope at theObservatoire de Haute-Provence (St-Michel l'Observatoire, France) andCORALIE.Based on observations collected at the Swiss 1.2 m Leonard Eulertelescopes at the European Southern Observatory (La Silla, Chile).Tables 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u.strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/1121
| 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
| Abundance analysis of two late A-type stars HD 32115 and HD 37594
We have performed abundance analysis of two slowly rotating, late A-typestars, HD 32115 (HR 1613) and HD 37594 (HR 1940), based on obtainedechelle spectra covering the spectral range 4000-9850 Å. Thesespectra allowed us to identify an extensive line list for 31 chemicalelements, the most complete to date for A-type stars. Two approaches toabundance analysis were used, namely a ``manual'' (interactive) and asemi-automatic procedure for comparison of synthetic and observedspectra and equivalent widths. For some elements non-LTE (NLTE)calculations were carried out and the corresponding corrections havebeen applied. The abundance pattern of HD 32115 was found to be veryclose to the solar abundance pattern, and thus may be used as anabundance standard for chemical composition studies in middle and late Astars. Further, its Hα line profile shows no core-to-wing anomalylike that found for cool Ap stars and therefore also may be used as astandard in comparative studies of the atmospheric structures of cool,slowly rotating Ap stars. HD 37594 shows a metal deficiency at the levelof -0.3 dex for most elements and triangle-like cores of spectral lines.This star most probably belongs to the delta Sct group. Based onobservations obtained at the 2-m telescope of Peak Terskol Observatorynear Elbrus mountain, International Center of Astronomical andMedical-Ecological Researches, Russia. Table 4 is only available inelectronic form at http://www.edpsciences.org
| 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.
| Structure and Mass of a Young Globular Cluster in NGC 6946
Using the Wide Field Planetary Camera 2 on board the Hubble SpaceTelescope, we have imaged a luminous young star cluster in the nearbyspiral galaxy NGC 6946. Within a radius of 65 pc, the cluster has anabsolute visual magnitude, MV=-13.2, comparable to the mostluminous young ``super star clusters'' in the Antennae merger galaxy.UBV colors indicate an age of about 15 Myr. The cluster has a compactcore (radius ~1.3 pc) surrounded by an extended envelope with apower-law luminosity profile. The outer parts of the cluster profilegradually merge with the general field, making it difficult to measure aprecise half-light radius Re, but we estimateRe~13 pc. Combined with population synthesis models, theluminosity and age of the cluster imply a mass of8.2×105 Msolar for a Salpeter initial massfunction (IMF) extending down to 0.1 Msolar. If the IMF islognormal below 0.4 Msolar, then the mass decreases to5.5×105 Msolar. Depending on modelassumptions, the central density of the cluster is between5.3×103 and 1.7×104 Msolarpc-3, comparable to other high-density star-forming regions.We also estimate a dynamical mass for the cluster using high-dispersionspectra from the HIRES spectrograph on the Keck I telescope. The HIRESdata indicate a velocity dispersion of 10.0+/-2.7 km s-1 andimply a total cluster mass within 65 pc of(1.7+/-0.9)×106 Msolar. Comparing thedynamical mass with the mass estimates based on the photometry andpopulation synthesis models, we find that the mass-to-light ratio is atleast as high as for a Salpeter IMF extending down to 0.1Msolar, although a turnover in the IMF at 0.4Msolar is still possible within the ~1 σ errors. Thecluster will presumably remain bound, evolving into a globularcluster-like object. Based on observations with the NASA/ESA HubbleSpace Telescope and with the W. M. Keck Telescope.
| Light curve shape variability of SZ cassiopeiae between 1978-1994
The aim of our investigation was to approach the problem ofidentification for possible variability of light curve shape in case ofthe classical Cepheid SZ Cassiopeiae. In order to perform such a studywe analysed eight observational data sets obtained through Vphotoelectrical photometry, covering a time base of 16 years. We appliedthe Fourier decomposition technique to each data set; the obtainedFourier coefficients were used to calculate the corresponding amplituderatios and phase differences. Their time behavior were finally studiedin order to search for evidences of the variability of the light curveshape.
| Elemental abundance analyses with DAO spectrograms - XXIII. The superficially normal stars 28 And (A7III) and 99 Her (F7V)
Elemental abundances of 28 And (A7III) and 99 Her (F7V), which havemodest rotational velocities, are derived in a manner consistent withprevious studies in this series of papers. The values for 28 And, aδ Scuti variable, show that it is slightly metal-poor, but not aclassical Am star. 99 Her, which is somewhat more metal-poor, has arather small microturbulence for its spectral type.
| Abundances of C, N, O, and other elements in the atmospheres of the δ Scuti variables 14 Aur, δ Sct, and HD 127986
Using high-resolution spectra, we have determined the abundances ofcarbon (logε(C)), nitrogen (logε(N)), oxygen (logε(O)),silicon (logε(Si)), sulphur (logε(S)), and some other elementsfor three δ Scuti stars. Logε(C) for all three stars andlogε(N) for δ Sct and HD 127986 are close to the solarvalues, while there appears to be a slight (0.15 dex) nitrogendeficiency for 14 Aur. The logε(O) values correspond to a 0.30-dexdeficiency for 14 Aur and δ Sct and a 0.20-dex deficiency for HD127986. The values of logε(Si) for the three stars are close tosolar, and the logε(S) values indicate a slight deficiency (0.10dex) for 14 Aur and HD 127986 and a 0.20-dex excess for δ Sct.Comparison of the elemental abundances for seven δ Scuti starswith those for Am stars shows that the mean deficiencies of C, N, and Oare smaller for pulsating δ Scuti stars than for Am stars withsimilar effective temperatures. The sulphur abundances are virtually thesame for both types of stars.
| 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
| Metal abundances of field A and Am stars
Detailed abundances of 9 field A and Am stars are derived for Mg, Ca,Sc, Cr, Fe, and Ni using high resolution spectroscopy. Most of oursample Am stars show the characteristic deficiencies of Ca and Sc on onehand, and the overabundances of the iron peak elements on the other,which is consistent with the predictions of the diffusion model for MainSequence or slightly evolved stars. There seems to be a correlationbetween abundances of Ca and Sc and the effective temperature for starsof similar age: the abundance of Ca increases with increasing masswhereas that of Sc decreases. Two of our Am stars have a differentabundance pattern: Ca is overabundant in the hot magnetic Am star o Pegand its abundance is nearly normal in the metallic giant star rho Pup.The other objects of our sample have globally a solar composition except28 And, which shows significant deficiencies for most the studiedelements. Based on observations collected at the Observatoire deHaute-Provence (France), and on data from the ESA\protect\linebreakHIPPARCOS astrometry satellite.
| On the cobalt abundances of early-type stars
Photographic region high-dispersion high signal-to-noise spectra of Aand F main sequence band stars which exhibit modest rotation show Co Ilines. In the hottest of these stars, we also found weak Co II lineswhose abundances are consistent with those from Co I lines. As a classthe Am stars have cobalt abundances which are greater than solar whilethe normal stars have solar values.
| Stability in the Light Curves of High-Amplitude delta Scuti Stars: Selected Monoperiodic Stars
We have analyzed all the reliable photometric data sets available in thebibliography for a selected sample of monoperiodic high-amplitude deltaScuti stars in order to study the stability of their light curves. Atotal of 169 data sets and more than 22,000 points have been consideredfor seven stars: ZZ Mic, EH Lib, BE Lyn, YZ Boo, SZ Lyn, AD CMi, and DYHer. The results do not reveal significant long-term changes ofamplitude of the light curves for any of these stars.
| Mode and period changes in pulsating stars near the main sequence : delta Scuti stars.
Not Available
| Mode identification and asteroseismology of delta Scuti stars
The use of multicolour photometry for mode identification in pulsatingstars is discussed. We present a new, statistically based, algorithm forfinding the best estimate of the spherical harmonic degree, and aconfidence level from which the uniqueness can be ascertained. Themethod is applied to some well-observed delta Sct stars with multicolourphotometry. We also propose an algorithm to deduce the effectivetemperature, luminosity and equatorial velocity from the observedfrequencies. We find that fixing the modes of at least some frequenciesis essential for a unique solution. The method is applied to a subset ofthe delta Sct stars which have a suitable number of frequencies and modeidentifications.
| Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars
We discuss a spectroscopic and photometric technique that enables theidentification and classification of field horizontal-branch (FHB) andother A-type stars, even from relatively low signal-to-noise ratiomedium-resolution spectra. This technique makes use of broadband UBVcolors predicted from model atmosphere calculations and Balmer lineprofiles and Ca II K equivalent widths determined from synthetic spectrato estimate the physical parameters T_eff, log g, and [Fe/H] for starsin the effective temperature range 6000-10,000 K. A comparison of ourmethod with high signal-to-noise ratio spectra of standard starsindicates a scatter in the derived parameters of sigma(T_eff)=+/-250 K,sigma(log g)=+/-0.14 dex, and sigma([Fe/H])=+/-0.12 dex. This precisionallows for a separation of low surface gravity FHB and other, generallyhigher surface gravity, A-type (and somewhat later) stars. We alsodevelop a synthetic-template comparison technique, which is veryeffective in the identification of metallic-line and peculiar A-typestars. A detailed investigation of the influence of noise in the spectraon the determination of physical parameters shows that, for spectra withsignal-to-noise ratios in the range 10
| The effective temperature scale of giant stars (F0-K5). I. The effective temperature determination by means of the IRFM
We have applied the InfraRed Flux Method (IRFM) to a sample ofapproximately 500 giant stars in order to derive their effectivetemperatures with an internal mean accuracy of about 1.5% and a maximumuncertainty in the zero point of the order of 0.9%. For the applicationof the IRFM, we have used a homogeneous grid of theoretical modelatmosphere flux distributions developed by \cite[Kurucz (1993)]{K93}.The atmospheric parameters of the stars roughly cover the ranges: 3500 K<= T_eff <= 8000 K; -3.0 <= [Fe/H] <= +0.5; 0.5 <= log(g) <= 3.5. The monochromatic infrared fluxes at the continuum arebased on recent photometry with errors that satisfy the accuracyrequirements of the work. We have derived the bolometric correction ofgiant stars by using a new calibration which takes the effect ofmetallicity into account. Direct spectroscopic determinations ofmetallicity have been adopted where available, although estimates basedon photometric calibrations have been considered for some stars lackingspectroscopic ones. The adopted infrared absolute flux calibration,based on direct optical measurements of stellar angular diameters, putsthe effective temperatures determined in this work in the same scale asthose obtained by direct methods. We have derived up to fourtemperatures, TJ, TH, TK and T_{L'},for each star using the monochromatic fluxes at different infraredwavelengths in the photometric bands J, H, K and L'. They show goodconsistency over 4000 K, and there is no appreciable trend withwavelength, metallicity and/or temperature. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of error and their effect on final temperatures. Wealso provide a comparison of the results with previous work.
| Broad-band JHK(L') photometry of a sample of giants with 0.5 > [Fe/H] > -3
We present the results of a three-year campaign of broad-band photometryin the near-infrared J, H, K and L' bands for a sample of approximately250 giant stars carried out at the Observatorio del Teide (Tenerife,Spain). Transformations of the Telescopio Carlos Sanchez systeminto/from several currently used infrared systems are extended to theredward part of the colour axis. The linearity of our photometric systemin the range -3 mag [Fe/H] >-3. Data of comparable quality previouslypublished have been added to the sample in order to increase thereliability of the relations to be obtained. We also provide mean IRcolours for giant stars according to spectral type.ables 1, 2 and 3 are only available in electronic form via the CDS(anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html
| Are metallic A-F giants evolved AM stars? Rotation and rate of binaries among giant F stars
We test the hypothesis of Berthet (1992) {be91} which foresees that Amstars become giant metallic A and F stars (defined by an enhanced valueof the blanketing parameter Delta m_2 of the Geneva photometry) whenthey evolve. If this hypothesis is right, Am and metallic A-FIII starsneed to have the same rate of binaries and a similar distribution ofvsin i. From our new spectroscopic data and from vsin i and radialvelocities in the literature, we show that it is not the case. Themetallic giant stars are often fast rotators with vsin i larger than 100kms(-1) , while the maximum rotational velocity for Am stars is about100 kms(-1) . The rate of tight binaries with periods less than 1000days is less than 30% among metallic giants, which is incompatible withthe value of 75% for Am stars - [Abt & Levy 1985] {ab85}).Therefore, the simplest way to explain the existence of giant metallic Fstars is to suggest that all normal A and early F stars might go througha short ``metallic" phase when they are finishing their life on the mainsequence. Besides, it is shown that only giant stars with spectral typecomprised between F0 and F6 may have a really enhanced Delta m_2 value,while all A-type giants seem to be normal. Based on observationscollected at Observatoire de Haute Provence (OHP), France.
| Extreme amplitude variations in 28 And
New simultaneous observations using the four uvby filters of theStroemgren photometric system have been collected in the year 1996 forthe low amplitude delta Sct star 28 And. During the course of theseobservations, the observed amplitude of the light curves is very smallas compared with any other data set available in the literature for thisstar. In particular, the actual amplitude is about 19 times less thanduring the last observing run, five years before. The frequency analysisof the data also reveals the existence of a secondary frequency nu _2.Hence, the monoperiodicity is not confirmed with the new data. Inaddition, the analysis of the phase shifts between observed lightvariations confirms the nonradial nature of the main pulsation of thisstar.
| Period changes of delta Scuti stars and stellar evolution
Period changes of delta Scuti stars have been collected or redeterminedfrom the available observations and are compared with values computedfrom evolutionary models with and without convective core overshooting.For the radial pulsators of Pop. I, the observations indicate (1/P)dP/dt values around 10(-7) year(-1) with equal distribution betweenperiod increases and decreases. The evolutionary models, on the otherhand, predict that the vast majority should show increasing periods.This increase should be a factor of about ten times smaller thanobserved. For nonradial delta Scuti pulsators of Pop. I, thediscrepancies are even larger. The behavior suggests that for theserelatively unevolved stars the rate of evolution cannot be deduced fromthe period changes. The period changes of most Pop. II delta Scuti (SXPhe) stars are characterized by sudden jumps of the order of Delta P/P ~10(-6) . However, at least one star, BL Cam, shows a large, continuousperiod increase. The variety of observed behavior also seems to excludean evolutionary origin of the changes. Model calculations show that theevolutionary period changes of pre-MS delta Scuti stars are a factor of10 to 100 larger than those of MS stars. Detailed studies of selectedpre-MS delta Scuti stars are suggested.
| Behaviour of calcium abundance in Am-Fm stars with evolution
Calcium abundance in the atmosphere of Am stars is examined as afunction of their evolutionary state within the main sequence. Newspectroscopic abundances as well as abundances obtained photometricallyby Guthrie (1987) are used, since they are mutually quite consistent.The main result of this work is that, contrary to earlier suggestions,calcium abundance does not tend to be larger in evolved Am stars than inunevolved ones, for objects distributed along a given evolutionary trackin the HR diagram. The trend appears to be the reverse, if it is presentat all. For our whole sample of Am stars, there is a significantcorrelation between calcium abundance and effective temperature, in thesense that the cooler objects are the most Ca-deficient, hence have themost pronounced Am peculiarity. This implies an apparent correlationbetween calcium deficiency and age, although the lack of Am starsyounger than log t = 8.6 seems real. Our results are fully consistentwith the low rate of Am stars observed in young clusters and withtheoretical predictions of time-dependent radiative diffusion (Alecian1996). Based on observations collected at Observatoire de Haute Provence(CNRS), France, and on data from the ESA HIPPARCOS astrometry satellite.
| Amplitude variations of the multimode nonradial δ Scuti pulsator 4 CVn
New photoelectric photometry of the δ Scuti variable 4 CVn revealslong-term slow variations of multimode pulsational frequencies and theiramplitudes. We have confirmed 5(f1, f2,f3, f5, f7) of the 7 frequenciesidentified in the literature. Besides presenting the long-termvariations of the different amplitudes, we have found three newsuspected frequencies in the new data. Although Blazhko effect and moderesonance along with its coupling between different nonradial modesthrough interaction can be reasonably used to explain the observedchanges of periods and amplitudes, it should be carefully checked andanalyzed before RR Lyr-like light curve shape and new pulsation modescan be established with certainty.
| Amplitude variations of the multimode nonradial delta Scuti pulsator 4 CVn.
Not Available
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Spectroscopic survey of delta Scuti stars. I. Rotation velocities and effective temperatures
Projected rotational velocities and effective temperatures for 68 deltaSct stars as well as 41 non-variable stars of similar spectral type andluminosity are presented here. The rotational velocities have beencalculated following the method developed in \cite[Gray (1992)]{ref38}and effective temperatures have been derived using the Balmer lineprofiles. The temperatures obtained from this method are shown to be inreasonable agreement with those calculated using the Infrared FluxMethod (IRFM) or spectrophotometric methods. This result has allowed usto use our temperatures to compare different uvby beta photometriccalibrations. We find that the calibration given by \cite[Moon \&Dworetsky (1985)]{ref72} is the most consistent. In the second part ofthis paper we have studied the relation between the pulsationalproperties (periods and amplitudes) and the physical parameters (v sin iand Teff). Where pulsation modes have been determined, thelow amplitude $\delta$ Scutis tend to be multimode (radial andnon-radial) pulsators, consistent with the theory that non-linearcoupling between modes acts to limit the amplitude in these stars. Wehave compared the distribution of v sin i for low amplitude $\delta$Scutis and non-variable stars. This shows the $\delta$ Scutis have abroader distribution in v sin i suggesting that a high rotation velocitymay favour pulsation. We find that the large amplitude delta Scuti starstend to have longer periods, cooler temperatures and lower rotationvelocities. Given that the large amplitude stars are also relativelyrare all the above are consistent with the hypothesis that these starsare more evolved (sub-giants) than the low amplitude delta Scutis (mainsequence or early post-main sequence).
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Androméda |
| Rektaszcenzió: | 00h30m07.30s |
| Deklináció: | +29°45'06.0" |
| Vizuális fényesség: | 5.23 |
| Távolság: | 56.754 parszek |
| RA sajátmozgás: | 43.4 |
| Dec sajátmozgás: | -56.3 |
| B-T magnitude: | 5.523 |
| V-T magnitude: | 5.246 |
Katalógusok és elnevezések:
|
