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# θ And (Theta Andromedae)

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 Unconstrained Astrometric Orbits for Hipparcos Stars with Stochastic SolutionsA considerable number of astrometric binaries whose positions on the skydo not obey the standard model of mean position, parallax, and linearproper motion were observed by the Hipparcos satellite. Some of themremain undiscovered, and their observational data have not been properlyprocessed with the more adequate astrometric model that includesnonlinear orbital motion. We develop an automated algorithm, based ongenetic optimization,'' to solve the orbital fitting problem in themost difficult setup, when no prior information about the orbitalelements is available (from, e.g., spectroscopic data or radial velocitymonitoring). We also offer a technique to accurately compute theprobability that an orbital fit is bogus, that is, that an orbitalsolution is obtained for a single star, and to estimate the probabilitydistributions for the fitting orbital parameters. We test this method onHipparcos stars with known orbital solutions in the catalog and furtherapply it to 1561 stars with stochastic solutions, which may beunresolved binaries. At a confidence level of 99%, orbital fits areobtained for 65 stars, most of which have not been known as binary. Itis found that reliable astrometric fits can be obtained even if theperiod is somewhat longer than the time span of the Hipparcos mission,that is, if the orbit is not closed. A few of the new probable binarieswith A-type primaries with periods 444-2015 days are chemically peculiarstars, including Ap and λ Bootis types. The anomalous spectra ofthese stars are explained by admixtures of light from the unresolved,sufficiently bright and massive companions. We estimate the apparentorbits of four stars that have been identified as members of the ~300Myr old Ursa Major kinematic group. Another four new nearby binaries mayinclude low-mass M-type or brown dwarf companions. Follow-upspectroscopic observations in conjunction with more accurate inclinationestimates will lead to better estimates of the secondary mass. Similarastrometric models and algorithms can be used for binary stars andplanet hosts observed by SIM and Gaia. The physical properties of normal A starsDesignating 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. Magnetospheres and Disk Accretion in Herbig Ae/Be StarsWe present evidence of magnetically mediated disk accretion in HerbigAe/Be stars. Magnetospheric accretion models of Balmer and sodiumprofiles calculated with appropriate stellar and rotational parametersare in qualitative agreement with the observed profiles of the Herbig Aestar UX Ori and yield a mass accretion rate of ~10-8Msolar yr-1. If more recent indications of anextremely large rotation rate for this object are correct, the magneticfield geometry must deviate from that of a standard dipole in order toproduce line emission consistent with observed flux levels. Models ofthe associated accretion shock qualitatively explain the observeddistribution of excess fluxes in the Balmer discontinuity for a largeensemble of Herbig Ae/Be stars and imply typically small mass accretionrates, <~10-7 Msolar yr-1. In orderfor accretion to proceed onto the star, significant amounts of gas mustexist inside the dust destruction radius, which is potentiallyproblematic for recently advocated scenarios of puffed'' inner dustwall geometries. However, our models of the inner gas disk show that forthe typical accretion rates we have derived, the gas should generally beoptically thin, thus allowing direct stellar irradiation of the innerdust edge of the disk. Elemental abundance analyses with DAO spectrograms. XXVII. The superficially normal stars theta And (A2 IV), epsilon Del (B6 III), epsilon Aqr (A1.5 V), and iota And (B9 V)The superficially normal stars theta And (A2 V), epsilon Del (B6 III),epsilon Aqr (A1.5 V), and iota And (B9 V), which have rotationallybroadened line profiles, are analyzed in a manner consistent withprevious studies of this series using 2.4 Åmm-1spectrograms obtained with CCD detectors and S/N >=200. Theirvariable radial velocities strongly suggest they are spectroscopicbinaries. As no evidence is seen for lines of their companions they areanalyzed as single stars. Their derived abundances are generally nearsolar. But those for theta And suggest that it is possibly a fastrotating Am star.Table 5 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/406/975 Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin iThis 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 On the effective temperatures and surface gravities of superficially normal main sequence band B and A starsEffective temperatures and surface gravities for 48 main sequence band Band A stars were found by matching optical region spectrophotometry andHγ profiles with the predictions of ATLAS9 solar composition modelatmospheres. When these values were compared with those found usingStrömgren uvbybeta photometry based on ATLAS6 model atmospheres, wefound a difference (photometry-spectrophotometry) of 25+/- 118 K for 29stars with 8000 K le Teff <= 10 050 K compared to 76 +/-105 K for 14 stars with 10 050 K <= Teff <= 17 000 K.The surface gravity scales are in agreement. These stars aresufficiently hot that their effective temperatures and surface gravitydeterminations are unaffected by discrepancies due to the choice ofMixing-Length or Canuto-Mazzitelli convection theories. CO 1st overtone spectra of cool evolved stars: Diagnostics for hydrodynamic atmosphere modelsWe present spectra covering the wavelength range 2.28 to 2.36 mu m at aresolution of Delta lambda = 0.0007 mu m (or R = 3500) for a sample of24 cool evolved stars. The sample comprises 8 M supergiants, 5 M giants,3 S stars, 6 carbon stars, and 2 RV Tauri variables. The wavelengthscovered include the main parts of the 12C16O v =2-0 and 3-1 overtone bands, as well as the v = 4-2 and 13CO v= 2-0 bandhead regions. CO lines dominate the spectrum for all the starsobserved, and at this resolution most of the observed features can beidentified with individual CO R- or P-branch lines or blends. Theobserved transitions arise from a wide range of energy levels extendingfrom the ground state to E/k > 20 000 K. We looked for correlationsbetween the intensities of various CO absorption line features and otherstellar properties, including IR colors and mass loss rates. Two usefulCO line features are the v = 2-0 R14 line, and the CO v = 2-0 bandhead.The intensity of the 2-0 bandhead shows a trend with K-[12] color suchthat the reddest stars (K-[12] > 3 mag) exhibit a wide range in 2-0bandhead depth, while the least reddened have the deepest 2-0 bandheads,with a small range of variation from star to star. Gas mass loss ratesfor both the AGB stars and the red supergiants in our sample correlatewith the K-[12] color, consistent with other studies. The data implythat stars with dot M_gas < 5x 10-7 Msuny-1 exhibit a much narrower range in the relative strengthsof CO 2-0 band features than stars with higher mass loss rates. Therange in observed spectral properties implies that there are significantdifferences in atmospheric structure among the stars in this sample.Figures 4-9, 11-14, 16, 17, 19-21, 23, 24 are only avalaible inelectronic form at http://www.edpsciences.org Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald ObservatoryThe Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission. Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statisticsThe 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 Research Note Hipparcos photometry: The least variable starsThe data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is 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/367/297 ICCD Speckle Observations of Binary Stars. XXIII. Measurements during 1982-1997 from Six Telescopes, with 14 New OrbitsWe present 2017 observations of 1286 binary stars, observed by means ofspeckle interferometry using six telescopes over a 15 year period from1982 April to 1997 June. These measurements constitute the 23dinstallment in CHARA's speckle program at 2 to 4 m class telescopes andinclude the second major collection of measurements from the MountWilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are alsopresented for 14 systems, seven of which have had no previouslypublished orbital analyses. Spectroscopy of Pre-Main-Sequence Candidates of Spectral Type AF in the Young Galactic Cluster IC 4996We present the results of a spectroscopic analysis of thepre-main-sequence (PMS) candidates in IC 4996, proposed by Delgado etal. Spectral types and heliocentric radial velocities are calculated for16 stars in the field observed by these authors, 13 of them located inthe region of the color-magnitude diagram where their proposed PMS starsare located. The estimated heliocentric radial velocity of the clusteris centered around -12+/-5 km s^-1. From the radial velocitydistribution, six stars are rejected as cluster members, one of themshowing spectral features characteristic of an Am star. The remaining 10stars are confirmed as cluster members: three B-type stars and seven PMSstars of spectral types A4-F0 (six stars) and early G (one star). One ofthe proposed PMS members clearly shows radial velocity and spectral typevariations, as well as relatively broad Hα absorption. The G-typecluster member is a weak-lined T Tauri star with strong Li Iλ6708 absorption [W_λ(Li I)~=0.26 Å]. These resultsstrongly support the presence in the cluster of a populated sequence ofPMS stars of AF spectral type. A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 StarsUltraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories. Averaged energy distributions in the stellar spectra.Not Available Effective temperatures of AP starsA new method of determination of the effective temperatures of Ap starsis proposed. The method is based on the fact that the slopes of theenergy distribution in the Balmer continuum near the Balmer jump fornormal" main sequence stars and chemically peculiar stars with thesame Teff are identical. The effective temperaturecalibration is based on a sample of main sequence stars with well knowntemperatures (\cite[Sokolov 1995]{sokolov}). It is shown that theeffective temperatures of Ap stars are derived by this method in goodagreement with those derived by the infrared flux method and by themethod of \cite[Stepien & Dominiczak (1989)]{stepien}. On the otherhand, the comparison of obtained Teff with Teffderived from the color index (B2-G) of Geneva photometry shows a largescatter of the points, nevertheless there are no systematicaldifferences between two sets of the data. Chemically peculiar stars in the field of NGC 2244Low-resolution long-slit spectra of reference stars, including MKKstandard stars and well-known chemically peculiar stars, are used todevelop a spectroscopic method for the detection of the 5200 {Angstroms} flux depression in CP stars. This new method is shown to beas sensitive a detection tool as the photometrical techniques, andprovides a higher resolution view of the excess blocking. Application tostars in the field of NGC 2244 allows us to estimate and eliminatereddening effects. CP stars detected in this field include two members(# 334 and # 276) of the very young stellar group NGC 2244 (age ~ 3 x10(6) yr) and two or three foreground stars (# 381, # 625 and maybe #629). # 334 and # 625 are strongly peculiar. Based on observationsobtained at the Observatoire du Haute--Provence (OHP), France Spectroscopic and photometric investigations of MAIA candidate starsIncluding our own observational material and the Hipparcos photometrydata, we investigate the radial velocity and brightness of suspectedMaia variable stars which are classified also in some examples aspeculiar stars, mainly for the existence of periodic variations withtime-scales of hours. The results lead to the following conclusions: (1)Short-term radial velocity variations have been unambiguously proved forthe A0 V star gamma CrB and the A2 III star gamma UMi. The stars pulsatein an irregular manner. Moreover, gamma CrB shows a multiperiodstructure quite similar to some of the best-studied neighbouring deltaScu stars. (2) In the Hipparcos photometry as well as in our photometricruns we find significant short- and long-term variations in the stars HD8441, 2 Lyn, theta Vir, gamma UMi, and gamma CrB. For ET And theHipparcos data confirm a short-period variation found already earlier.Furthermore, we find changes of the colour index in theta Vir and gammaCrB on a time-scale of days. (3) No proofs for the existence of aseparate class of variables, designated as Maia variables, are found. Ifthe irregular behaviour of our two best-investigated stars gamma CrB andgamma UMi is typical for pulsations in this region of theHertzsprung-Russell diagram, our observational runs are too short andthe accuracy of the measurements too low to exclude such pulsations inthe other stars, however. (4) The radial velocities of the binariesalpha Dra and ET And have been further used for a recalculation of theorbital elements. For HD 8441 and 2 Lyn we estimated the orbitalelements for the first time. (5) Zeeman observations of the stars gammaGem, theta Vir, alpha Dra, 4 Lac, and ET And give no evidence of thepresence of longitudinal magnetic field strengths larger than about 150gauss. Based on spectroscopic observations taken with the 2\,m telescopeat the Th{ü Identification of lambda Bootis stars using IUE spectra. I. Low resolution dataAn analysis of the stars included in the catalogue of lambda Bootisstars by Paunzen et al. (1997) and which also have IUE observations ispresented here. Population I A-F type stars as well as field horizontalbranch stars were also included in the analysis. Using line-ratios ofcarbon to heavier elements (Al and Ni) allows us to establishunambiguous membership criteria for the lambda Bootis group. Tables 1-3are only available in electronic form at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html The absolute magnitude of the early type MK standards from HIPPARCOS parallaxesWe analyse the standards of the MK system with the help of Hipparcosparallaxes, using only stars for which the error of the absolutemagnitude is <= 0.3 mag. We find that the main sequence is a wideband and that, although in general giants and dwarfs have differentabsolute magnitudes, the separation between luminosity classes V and IIIis not clear. Furthermore, there are a number of exceptions to thestrict relation between luminosity class and absolute magnitude. Weanalyse similarly the system of standards defined by Garrison & Gray(1994) separating low and high rotational velocity standards. We findsimilar effects as in the original MK system. We propose a revision ofthe MK standards, to eliminate the most deviant cases. Based on datafrom the ESA Hipparcos astrometry satellite A catalogue of [Fe/H] determinations: 1996 editionA 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 The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NMA spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%. Be stars in open clusters I. uvbyβ photometry.We present uvbyβ photometry for Be stars in eight open clusters andtwo OB associations. It is shown that Be stars occupy anomalouspositions in the photometric diagrams, which can be explained in termsof the circumstellar continuum radiation contribution to the photometricindices. In the (b-y)_0_-M_V_ plane Be stars appear redder than the nonemission B stars, due to the additional reddening caused by the hydrogenfree-bound and free-free recombination in the circumstellar envelope. Inthe c_0_-M_V_ plane the earlier Be stars present lower c_0_ values thanabsorption-line B stars, which is caused by emission in the Balmerdiscontinuity, while the later Be stars deviate towards higher c_0_values, indicating absorption in the Balmer discontinuity ofcircumstellar origin. The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51. The Consistency of Stromgren-Beta Photometry for Northern Galactic Clusters. II. Praesepe and NGC 752We have measured stars in Praesepe and NGC 752 in aninternally-consistent Stromgren-Beta system. This system is based inlarge part on published Hyades and Coma measurements. On comparing ourPraesepe results to those of Crawford and Barnes (1969, AJ, 74, 818), wefind that the published color indices require corrections of 10-18 mmagto put them on the Hyades-Coma system. This deduction applies for b-y,m_1 and Beta (but not c_1). For the NGC 752 data of Crawford and Barnes(1970, AJ, 75, 946), we obtain a nonzero correction only for Beta. Thiscorrection is about 9 mmag. Also for NGC 752, we find that the data ofTwarog (1983, ApJ, 267, 207) require corrections ranging from 4-17 mmag,with all Stromgren indices being affected and the largest correctionbeing for m_1. These corrections resolve the long-standing problem posedby the differences between the Twarog and Crawford-Barnes data. Forthree published sources of V magnitudes, we obtain offsets ranging from-14 to +27 mmag relative to our zero point, and we suggest that suchoffsets are fairly common in published photometry for galactic clusters.For Praesepe, we use new and corrected data to test for a c_1 anomalyand is indistinguishable from Coma in that regard. (SECTION: StellarClusters and Associations) The Relation between Rotational Velocities and Spectral Peculiarities among A-Type StarsAbstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&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. The determination of T_eff_ of B, A and F main sequence stars from the continuum between 3200 A and 3600 A.A method of determination of the effective temperature of B, A and Fmain sequence stars is proposed, using the slope of the continuumbetween 3200A and 3600A. The effective temperature calibration is basedon a sample of stars with energy distributions known from UV to the red.We have determined the Balmer jump and the effective temperatures for235 main sequence stars. The temperatures found have been compared withthose derived by Underhill et al. (1979), Kontizas & Theodossiou(1980), Theodossiou (1985), Morossi & Malagnini (1985). Thecomparison showed good agreement for most of the stars in common. On theother hand, the temperatures derived from the reddening-free colourfactor QUV, from the colour index (m1965-V) and from (B-V), given inGulati et al. (1989), are systematically lower than our temperatures,however the differences are within one-sigma error. Variability investigations of possible Maia stars.Series of spectrograms and a limited number of photometric measurementsof selected early-type stars have been used to search in the measuredradial velocities and light curves for stellar pulsations withtimescales of a few hours. For these stars, located in the HR diagrambetween the β Cep and the δ Scu stars and designed sometimesas Maia variables, the presence of pulsations is claimed to be a commonproperty. In our sample we found no hints for a general existence ofsuch pulsations. RV-variations with the expected short-term scale couldbe observed for only two of the program stars, γ UMi and γCrB. The variations are highly irregular in amplitude and frequency. Onthe other hand, for both stars a typical mean timescale of theRV-variation of about 2.4hr has been found which gives some hints topossibly common physical causes of short-term variations of stars inthis part of the HR diagram. The RV-variation of γ CrB in theyears 1992/93 could be attributed to a rotational splitting of nonradialpulsations. Compositional differences among the A-type stars. 2: Spectrum synthesis up to V sin i = 110 km/sThe results of an abundance analysis of 15 early A-type stars arepresented here. These stars have u sin i on the range 6 to 109 km/s andall but one of them (an Am star) are classified as normal. Reliableabundances (uncertainties about a quarter dex or less) are obtained fortwelve elements. Considerable star-to-star abundance variations arepresent among both the narrow lined and broader lined stars. Mostelements have abundances which scale with those of iron. Carbon andcalcium are interesting exceptions. Carbon abundances seem to beanti-correlated with those of iron, while calcium abundances may exhibita more complex behavior. Heavy elements seem enhanced for most stars. What is Normal among the A-StarsNot Available
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