K. Yüce

Carbon deficiencies in the primaries of some classical Algols

The equivalent widths (EWs) of the C IIλ4267 A line were measured for the mass-gaining primary stars of 18 Algol-type binary systems. The EWs of the gainers were compared with the EWs of single standard stars that have the same effective temperature and luminosity class. This comparison clearly indicates that the EWs of the gainers are systematically smaller than those of the standard stars. The primary components of the classical Algols, located in the main-sequence band of the Hertzsprung–Russell diagram, appear to be carbon-poor stars. We estimate [NC/Ntot] relative to the Sun as −1.91 for GT Cep, −1.88 for AU Mon and −1.41 for TU Mon, indicating poorer carbon abundance. An average differential carbon abundance has been estimated to be −0.82 dex relative to the Sun and −0.54 dex relative to the main-sequence standard stars. This result is taken to be an indication of material transferring from the evolved less-massive secondary components to the gainers, such that the CNO cycle processed material changed the original abundance of the gainers. There appear to be relationships between the EWs of the CII λ4267 A line and the rates of orbital period increase and mass transfer in some Algols. As the mass transfer rate increases, the EW of the C II line decreases. This indicates that accreted material has not yet been completely mixed in the surface layers of the gainers. This result supports the idea of mixing as an efficient process to remove the abundance anomaly built up by accretion. The chemical evolution of the classical Algol-type systems could lead to constraints on the initial masses of the less massive, evolved, mass-losing stars.

Wavelengths and oscillator strengths of Xe II from the UVES spectra of four HgMn stars

Aims. In spite of large overabundances of Xe ii observed in numerous mercury-manganese (HgMn) stars, Xe ii oscillator strengths are only available for a very limited number of transitions. As a consequence, several unidentified lines in the spectra of HgMn stars could be due to Xe ii. In addition, some predicted Xe ii lines are redshifted by about 0.1 A from stellar unidentified lines, raising the question about the wavelength accuracy of the Xe ii line data available in the literature. For these reasons we investigated the Xe ii lines lying in the 3900–4521 A, 4769–7542 A, and 7660–8000 A spectral ranges of four well-studied HgMn stars. Methods. We compared the Xe ii wavelengths listed in the NIST database with the position of the lines observed in the high-resolution UVES spectrum of the xenon-overabundant, slowly rotating HgMn star HR 6000, and we modified them when needed. We derived astrophysical oscillator strengths for all the Xe ii observed lines and compared them with the literature values, when available. We checked the stellar atomic data derived from HR 6000 by using them to compute synthetic spectra for three other xenon-overabundant, slowly rotating HgMn stars, HD 71066, 46 Aql, and HD 175640. In this framework, we performed a complete abundance analysis of HD 71066, while we relied on our previous works for the other stars. Results. We find that all the lines with wavelengths related to the 6d and 7s energy levels have a corresponding unidentified spectral line, blueshifted by the same quantity of about 0.1 A in all the four stars, so that we identified these lines as coming from Xe ii and modified their NIST wavelength value according to the observed stellar value. We find that the Xe ii stellar oscillator strengths may differ from one star to another from 0.0 dex to 0.3 dex. We adopted the average of the oscillator strengths derived from the four stars as final astrophysical oscillator strength.

Elemental abundance analyses with DAO spectrograms - XXV. The superficially normal B and A stars

Elemental abundances analyses of the superfically normal B and A stars α Dra (A0 III), τ Her (B5 IV), γ Lyr (B9 III), and HR 7926 (B8 II-III) are performed consistent with previous studies of this series using spectrograms obtained with Reticon and CCD detectors. Comparisons of the first two analyses with those of the same stars performed earlier in this series which used mostly coadded photographic plates show the general consistency of the derived elemental abundances. A slight increase in the adopted effective temperature produces a corresponding increase in the derived abundances. In these stars the He/H ratios are found to be close to solar. Except for γ Lyr the metals show for the most part marginally subsolar abundance values. But this star has Al, Ca, Sc, and Sr abundances that are substantially underabundant as well as other underabundant values.

\alpha

Detailed analyses of high-dispersion, high signal-to-noise spectra enable astronomers to infer many stellar properties. We study nonmagnetic normal and chemically peculiar B, A, and F stars to understand the details of their optical region abundances via graphical techniques using two kinds of figures for 32 elements. By characterizing the anomalies of the mercury-manganese (HgMn) and the metallic-line (Am) stars, we provide major theoretical tests. We confirmed the known Hg dichotomy between HgMn stars, which are greatly overabundant, and the Am stars with normal abundances. Further P, Ga, Xe, Pt, and Au values were only overabundant for some HgMn stars, and lines of the rare earth elements, such as Sm and Eu, were seen only in some Am and normal stars. These observations might be due in some cases to changes in the major ionization state of atoms in the relevant stellar atmosphere. That some HgMn stars with large Ga overabundances have positions close in the H-R diagram to HgMn stars that lack Ga II lines in the optical region suggests a dichotomy similar to Hg with a boundary close to, but not identical, to that for Hg. The spread of the abundance anomalies for a given element tends to be smaller among the Am stars than among the HgMn stars. Star-to-star differences are superimposed upon abundance trends.

Draconis,

The study of the elemental abundances of double-lined spectroscopic binaries should provide information on the chemical differentiation of a once uniform prestellar nebula. To determine the effective temperatures and surface gravities of the primary and secondary stellar components of HR 104 and ? Aql, we used parameters derived from their orbital analyses and the requirement of equal abundances derived from Fe I and Fe II lines. For constraints we had optical region spectrophotometry for ? Aql and the large equivalent width ratios for the many spectral metal lines which were produced in both stellar atmospheres for HR 104. Since the primary stars were much brighter than the secondary stars, the abundances are considerably better determined for the primary stars. For HR 104 A we found Teff?=?9875?K, log?g?=?4.26, and ??=?1.7?km?s-1; for HR 104 B Teff?=?7200?K, log?g?=?4.26, and ??=?0.6?km?s-1; for ? Aql A Teff?=?10400?K, log?=?3.63, and ??=?0.3?km?s-1; and for ? Aql B Teff?=?10250?K, log?=?4.20, and ??=?1.9?km?s-1. The abundances of HR 104 A, HR 104 B, and ? Aql A are best described as the solar pattern. Those of ? Aql B suggest a weak nonmagnetic CP star pattern. While there is no trace of the Hg II 3984 line for ? Aql, the most extreme observed abundance anomalies for the secondary are those of Ca, V, Mn, and Ni. Further study of this hot marginal Am star could provide insights into the origin of the nonsolar chemical abundances.

\tau

Supergiants are the most luminous stars in galaxies that are currently forming many stars. Reliable abundance determinations, for the most part, reflect the values of the interstellar material out of which they formed. Thus, they can be used to trace the chemical history of their parent galaxies. This study derived the stellar atmospheric parameters and elemental abundances of the early spectral type supergiants 4 Lac (B9 Iab) (HR 8541, HD 212593) and n Cep (A2 Ia) (HR 8334, HD 207260) from Reticon and CCD exposures obtained with the long camera of the 1.22 m telescope of the Dominion Astrophysical Observatory in Victoria, British Columbia. They cover 3830–4950 A with signal-to-noise ratios of at least 200 and a 2 pixel resolution of 0.072 A. The spectra were measured with the graphics spectroscopic analysis program REDUCE (G. Hill & W. A. Fisher 1986, Publ. Dominion Astrophys. Obs., 16, 193). The tailored analyses were performed using the LTE plane-parallel model atmospheres code ATLAS9 (R. L. Kurucz 1993, Kurucz CD-ROM 13 [Cambridge: Smithsonian Astrophys. Obs.]). They are similar to those performed by K. A. Venn (1995, ApJS, 99, 659) and B. Albayrak (2000, A&A, 364, 237), who studied supergiants with similar and cooler effective temperatures. The study of 4 Lac extends this type of analysis to a slightly hotter effective temperature. For weak features, the lines were measured using profiles whose width was found from medium-strength unblended lines to aid the process of trying to deconvolve blended lines. For each spectrogram, I identified the cleanest spectral features and found the radial velocity using the laboratory wavelengths. The remaining lines were identified with A Multiplet Table of Astrophysical Interest (C. E. Moore 1945, Princeton: Princeton Univ. Obs.) and more recent references. The adopted values Teff p 10,250 K and log g p 1.85 for 4 Lac and Teff p 8400 K and log g p 1.10 for n Cep were determined using the wings of Hb, and Fe i/ii and Si ii/iii ionization equilibria for 4 Lac and the wings of Hb and Fe i/ii and Cr i/ii ionization equilibria for n Cep. A microturbulence of 2.8 km s for 4 Lac was found from Fe ii lines using WIDTH9 1