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Heavy calcium in CP stars
Large wavelength shifts of infrared triplet lines of CaII have beenobserved in the spectra of HgMn and magnetic Ap stars. They have beenattributed to the heavy calcium isotopes, including 48Ca. Onemember of the triplet, ?8542, had been either unavailable, or ofpoor quality in earlier spectra. The present material shows conclusivelythat the stellar ?8542 shifts are consistent with aninterpretation in terms of 48Ca. We find no relation betweenisotopic shifts of the CaII triplet lines, and those of HgII?3984. There is a marginal indication that the shifts areanticorrelated with the surface field strengths of the magnetic stars.We see sparse evidence for 48Ca in other chemically peculiarstars, for example, Am stars, metal-poor stars or chemically peculiarred giants. However, the sample is still very small, and the wavelengthsof all three triplet lines, including those in the Sun, show slightpositive shifts with respect to terrestrial positions.Some profiles of the CaII infrared triplet in the magnetic stars showextensive wings beyond a well-defined core. We can obtain reasonablefits to these profiles using a stratified calcium abundance similar tothat used by previous workers. There is no indication that either thestratification or the Zeeman effect significantly disturbs themeasurement of isotope shifts.Based on observations obtained at the European Southern Observatory,Paranal and La Silla, Chile [ESO programmes 076.D-0169(A) and076.C-0172(A)].E-mail: cowley@umich.edu (CRC); shubrig@eso.org (SH);castelli@ts.astro.it (FC); fgonzalez@casleo.gov.ar (JFG); bwolff@eso.org(BW)
| The Ca II infrared triplet as indicator of anomalous Ca isotopic mixture in HgMn stars
For the first time we present observational evidence for an anomalousisotopic structure of Ca II in mercury-manganese (HgMn) stars. Thecentroid wavelengths of Ca II infrared triplet lines in a number ofstars have been found redshifted with respect to the centroids of theterrestrial Ca II lines. The record holder is the star HD 175640 forwhich the measured wavelength is consistent with Ca II being present inthe atmosphere entirely in form of the heaviest stable isotope48Ca. This is a very striking result as 48Ca makesup only 0.187% of the terrestrial Ca mixture.Based on observations obtained at the European Southern Observator, LaSilla and Paranal, Chile (ESO programme Nos. 65.L-0316 and 67.D-0579).
| Vertical distribution of chromium in the atmospheres of HgMn stars
We use multiplet 30 Cr II lines in the wings of Hbeta totest the hypothesis of an anomalous concentration of Cr in the upperlayers of the atmospheres of a sample of 10 HgMn stars. These lines areat different distances from the H_beta line center and are thereforeformed at different depths in the stellar atmosphere. Except for HD49606, all HgMn stars show an increase in Cr abundance with height inthe stellar atmosphere. A similar vertical distribution of Cr, but lesspronounced, has been previously found in Am stars. In contrast, novariation of Cr abundance with the depth has been found for the normallate B-type star HD 196426 and the weak magnetic late B-type star HD168733. It is possible that in HgMn stars the vertical stratificationparameter, a, depends on T_eff, with the strongest vertical gradientbeing found in the hotter stars. No correlation was found between a andthe average stellar abundance log varepsilon (Cr/H).Based on observations obtained at the European Southern Observatory, LaSilla and Paranal, Chile (ESO programmes Nos. 62.L-0348, 65.I-0644,67.D-0579).
| On the elemental abundance and isotopic mixture of mercury in HgMn stars
Optical region spectra of 31 HgMn stars have been studied for theabundance and isotope mixture of mercury. In the course of theinvestigation the lines Hg I lambda 4358 and Hg Ii lambda lambda3984,6149 have been studied, with abundances established for all threelines in several HgMn stars. The mercury isotope mixture has beendetermined from high resolution spectra of the lambda 3984 line.Possible signs of an ionization anomaly have been detected by thecomparison of the abundance derived from the Hg I line and the Hg Iilines in seven of the observed HgMn stars. A possible correlation of themercury abundance with Teff has been detected. Possible signsof a weak anticorrelation of the manganese and mercury abundance in HgMnstars have been found, which could be interpreted as a sign ofinhomogeneous surface distribution of these elements. For a number ofthe HgMn stars in this study the mercury abundance and isotope mixtureare reported for the first time.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| Evidence of decay of the magnetic fields of AP stars
Data obtained in the Geneva photometric system (Rufener, 1981) andappropriate calibrations of this system in terms of surface magneticfield and gravity are used to provide, on the basis of 708 field andcluster Ap stars, observational evidence that these stars undergo decayof their magnetic field on an evolutionary timescale. Justifications aregiven for the application of a photometric gravity calibration topeculiar stars. The dependence of the photometrically estimated surfacemagnetic field on gravity is found to differ markedly from availabletheoretical calculations. HgMn stars are found to show the same trend,strengthening the impression that they might be slightly magnetic.He-weak stars do not.
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