Lithium Abundances in the Atmospheres of SLR C-Giants WZ Cas and WX Cyg from Resonance and Subordinate Li I Lines

Lithium abundances in the atmospheres of the super Li-rich C-giants WZ Cas and WX Cyg are derived by the spectral synthesis technique using the Li I resonance line at λ670.8 nm and three subordinate lines at λλ 812.6, 610.4 and 497.2 nm. The differences between the Li abundances derived from the λ670.8 nm line and the λλ 497.2, 812.6 nm lines do not exceed ±0.5 dex. The lithium line at λ610.4 nm provides typically lower abundances than the resonance line (by ≈ 1 dex). The mean LTE and NLTE Li abundances from three Li I lines (excluding λ610.4 nm) are 4.7, 4.9 for WZ Cas, and 4.6, 4.8 for WX Cyg, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Lithium in chemically peculiar CP stars with magnetic fields

The problem of lithium in chemically peculiar Ap-CP stars has been the subject of debate for many years. The main reason for this is a lack of spectral observations of Ap stars in the neighborhood of the lithium resonance doublet Li I 6708 Å. An international cooperation project on “Lithium in cool CP stars with magnetic fields” was started in 1996. Systematic observations of CP stars in spectral regions of the 6708 Å and 6103 Å lines at the ZTSh (CrAO), CAT (ESO), Feros (ESO), and the 74″ telescope of the Mount Stromlo Observatory (Australia) have been used to analyze spectra of several CP stars studied by the way the 6708 Å lithium line varies with the stars’ rotational phase. Monitoring of the spectra of the oscillating CP stars (group I) HD 83368, HD 60435, and HD 3980, for which significant Doppler shifts of the Li I 6708 Å line are observed led to the discovery of “lithium spots” on the surface of these stars whose positions are related to the magnetic field structure. Models of the surfaces of these stars with the special program “ROTATE” based on the profiles of the Li I 6708 Å line are used to estimate the size of the spots, their positions on the stars’ surface, and the lithium abundances in these spots. A detailed analysis and modelling of the spectra of slowly rotating oscillating CP stars with strong, invariant lithium 6708 Å emission, including blending with lines of the rare earth elements, reveals an enhanced lithium abundance, with the abundance determined from the lithium 6103 Å line being higher than that determined from the 6708 Å line for all the stars. This may indicate vertical stratification of lithium in the atmospheres of CP stars with an anomalous isotopic composition (⁶Li/⁷Li = 0.2–0.5). HD 101065, an ultraslow rotator (vsini ≈ 1.5) visible from the poles and with powerful oscillations which cause pulsating line broadening in its spectrum, is unique among these stars. The amount of lithium in the atmosphere of HD 101065 logN(Li) = 3.1 on a scale of logN(H) = 12.0 and the isotope ratio ⁶Li/⁷Li ≈ 0.3. The high estimates of ⁶Li/⁷Li may be explained by the production of lithium in spallation reactions and the preservation of surface ⁶Li and ⁷Li by strong magnetic fields in the upper layers of the atmosphere near the magnetic poles. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 463–492 (August 2007).     

Identification of absorption lines of rare-earth elements in the region of the spectrum λλ 610.25–610.57 nm roAp stars,HD 101065, HD 134214, HD 137949, and HD 24712

In the spectral region λλ = 610.25−610.57 nm of the roAp star HD 101065, we performed the identification of the rare-earth element absorption lines absent from the atomic spectral line databases VALD and DREAM. The identified lines were used for calculating the synthetic spectra of the roAp stars HD 137949, HD 134214, and HD 24712. The upper limit of the identified line estimates was determined. The rotation/pulsation parameter νsini and magnetic field modulus were determined using the lines Nd III 669.083 nm and Ca I 616.217 nm. The element abundance in the roAp stars HD 134214 and HD 24712 was determined for the first time using Nd III lines. Calculations were carried out with the help of the code SynthM developed by S.A. Khan.     

Spectral observations using a BTA telescope of chemically peculiar stars in the spectral region near the Li I (6708 Å) resonance doublet

New spectral observations of chemically peculiar (CP) magnetic stars were obtained using an NES echelle spectrometer with a BTA telescope in the Special Astrophysical Observatory (Russian Academy of Sciences). Several stars were shown to have anomalous Li abundances. Testing and monitoring the stars with Doppler shifts Vsini > 10 km/s indicated that the lithium 6708 Å line was variable in the spectra of some roaAP-CP stars. To distinguish variable features in the spectra, the dispersogram technique was used. The most peculiar among the stars studied is HD 12098. The strong and variable lithium 6708 Å line was detected in the spectrum of this star. The star has been shown to have greatly different lithium abundances in two rotation phases corresponding to opposite surface areas. As mentioned earlier, a similar behavior of the Li blend was found in the spectra of HD 83368 and HD 60435 which have lithium spots on their surface. Spectral observations of slowly rotating CP stars with the Doppler shifts Vsini < 10 km/s revealed the strong and nonvariable lithium 6708 Å line in the spectra of these stars. Quantitative spectral analysis using the Li I 6708 Å resonance doublet and the Li I 6103 Å line shows the lithium abundance, as determined by the 6103 Å line, to be somewhat greater than that determined by the 6708 Å line. A higher ratio of ⁶Li/⁷Li amounting to ～0.3–0.5 was found in these stars. ⁶Li production is assumed to be due to spallation reactions on the surface of magnetic CP stars; this isotope ratio remained in strong magnetic fields.     

X-ray Spectroscopy of Active Stars with ASCA and BeppoSAX

We discuss representative cases of X-ray spectra of active stars obtained with ASCA and BeppoSAX. We focus in particular on our own observations of the RS CVn binaries γ And and UX Ari, of the BY Dra eclipsing binary HD9770, and of the young stars AB Dor and HD35850. This revised version was published online in July 2006 with corrections to the Cover Date.     

The violet opacity in the red peculiar stars (II)

Moderate dispersion (25-35 Å mm^–1) spectra were obtained from two carbon stars, V Cyg and WZ Cas, in a wide range of wavelengths (3400-6800 Å) with the echelle-spectrometer, ZEBRA, of the 6 m telescope and two-dimensional photon-counting system. Spectral feature identification was carried out from 3850 to 6200 Å. Most of the bands are due to C₂, SiC₂, and CN, however, particularly in WZ Cas, moderate atomic lines of the iron peak and s-process elements are also found. WZ Cas is a so-called lithium star, however, we have found no evidence for a strong line of Li. The spectra of V Cyg contain an emission line of H.     

Observing Boron in Metal-Poor Stars

A new sample of 7 stars ranging in metallicity from [Fe/H] = −2.0 to [Fe/H] = −0.75 has been analyzed in the boron spectral region. The targets were selected according to the availability (in the literature) of their lithium and beryllium abundances, because the simultaneous knowledge of LiBeB in the same targets is a powerful diagnostic for testing depletion and internal mixing predicted by different stellar structure models. Two stars (HD 94028 and HD 194598), characterized by similar Li contents, are found to have also similar B abundances, despite a 0.3 dex difference in their Be abundances claimed by Thorburn and Hobbs (1996). Four stars out of 7 are characterized by strongly depleted Li and Be abundances: 2 of them (HD 2665 and HD 3795) are also significantly B-depleted, while two others (HD 106516 and HD 221377) have near normal B abundances despite being depleted by a factor ≥ 10 in both Li and Be abundances. These stars place strong constraints on the nature and depth of the mixing processes responsible for their light element abundances. The 7th star (HD 160617) shows the remarkable aspect of deficient B, probably deficient Be, and completely normal Li. No stellar destruction mechanism can explain this. Rather, chemical inhomogeneities in the halo could be the cause. This revised version was published online in July 2006 with corrections to the Cover Date.     

Anomalous abundance of lithium in the roAp star HD 12098 recently discovered in the northern hemisphere of the sky

Spectral observations of Ap-CP stars with the BTA (Special Astronomical Observatory, Russian Academy of Sciences) using the NES echelle spectrometer have revealed several stars with an anomalous lithium abundance. The oscillating star HD 12098, which is the first roAp star in the northern hemisphere of the sky, merits special attention. Strong, variable LiI 6708 Å line was observed in the spectrum of this star. There are not enough observations for a reliable analysis by Doppler mapping, but there are enough to indicate the presence of lithium spots on the surface of this star similar to the roAp stars HD 83368 and HD 60435, on whose surfaces spots with a high lithium abundance have been reliably detected. Parameters for a model of its atmosphere have been chosen using the method of synthetic spectra based on atmospheric models including lines from the VALD list and several additional blended REE lines calculated by the authors. The profile of the lithium LiI 6708 Å blend has been calculated taking the magnetic field into account using the SYNTHM code. A lithium abundance has been determined for two phases of the rotation of HD 12098 that is anomalously high compared to the solar and meteoritic abundances. The large difference in the lithium abundance in the two phases (in two different regions on the star's surface) exceeds 0.5 dex and is very close to that which we have found by analyzing the spectra of the roAp stars HD 83368 and HD 60435. Thus, we have discovered yet another roAp star, HD 12098, with lithium spots on its surface. Translated from Astrofizika, Vol. 51, No. 4, pp. 607–616 (November 2008).     

Elemental abundance analyses with DAO spectrograms – XXII. The B9–A3 stars λ Ursae Majoris, 59 Herculis, 14 Cygni and 29 Cygni

Elemental abundances of the moderately rotating B9–A3 stars λ UMa, 59 Her, 14 Cyg and 29 Cyg have been derived in a consistent manner with previous studies of this series from spectrograms obtained with Reticon and CCD detectors. The derived elemental abundances show that λ UMa is a mild Am star, while 59 Her is slightly metal-rich. Although 14 Cyg has values closer to solar than these stars, its subsolar Ca and Sc abundances indicate that it might be the hottest known hot-Am star. 29 Cyg is a metal-poor λ Boo star.     

Comparison of UV spectra from solar-type stars

We compare high-resolution spectra from the Sun and the four solar-type stars 16 Cyg A, 16 Cyg B, HD 32008, HD 34411 obtained with IUE in the wavelength range 2650–2930 Å. The comparison is made for peak intensities between absorption lines. At the level of accuracy of the IUE observations, the stars 16 Cyg A, 16 Cyg B, HD 34411 are indistinguishable from the Sun, in particular the Mgii resonance line profiles are identical. HD 32008 is not a solar analog but is evidently of late G to early K spectral type.Based on observations with the International Ultraviolet Explorer collected at the Villafranca Satellite Tracking Station of the European Space Agency.     

WR stars with the Ovi λλ3811, 3834 emission doublet

The catalog of the classical WR stars which have the emission doublet Ovi 3811, 3834 in their optical spectra (the catalog of the WR-Ovi stars) and the results of the spectroscopic investigations of the WR-Ovi stars HD 16523, HD 17638, and HD 192103 are presented. Rapid spectral variability of the emission doublet Ovi 3811, 3834 in the spectra of WR-Ovi stars HD 16523, HD 17638, and of the emission band 3680-3780 Å in the spectra of the WR-Ovi star HD 16523 is observed. It is shown that spectral sub-types of the stars HD 16523 and HD 17638 as estimated from different criteria are uncertain. We argue that the WR-Ovi stars HD 16523 and HD 17638, the optical spectra of which display emission doublet Ovi 3811, 3834, may be considered as WO5 stars. The sub-type WO5 is proposed for the first time. Classification criteria of the WO5 sub-type are represented. The possible contribution of the ions Heii to the emission at 3811 Å and 3834 Å is investigated. Thez-distributions of WR-Ovi stars and WR stars with the probable relativistic companions are found to be similar.     

Analysis of the lithium lines in the atmosphere of the roAp star HD 24712

We use the synthetic spectrum technique to analyze two lithium lines in the spectrum of the roAp star HD 24712. The synthetic spectra are calculated in the ranges λλ 610.2–610.4 nm and 670.5–670.8 nm. We take into account the magnetic splitting of the lines and their blending by the lines of rare-earth elements. The effect of the magnetic field on absorption lines is estimated by the synthetic spectrum software SynthM developed by S.A. Khan. The upper limit for the lithium abundance turns out to be log N/N _tot = ?10.0.     

Analysis of the Spectra of Two Pleiades Brown Dwarfs: Teide 1 and Calar 3

Results of the numerical simulation of spectra of the Pleiades brown dwarfs Calar 3 and Teide 1 are discussed. Synthetical spectra were computed for several model atmospheres from a grid of Allard and Hauschildt (1995). From the comparison of computed and observed spectra we have found that: – the spectrum of Teide 1 may be reasonably well fitted by JOLA in the visible region, including the spectral regions around the Li I lines at λλ 670.8 and 812.6 nm. – The structure of absorption bands observed in the spectrum of Teide 1 and Calar 3 depends mainly on T_eff. The dependence on gravity is much weaker. – A comparison of observed and computed spectra shows that effective temperatures of these Pleiades brown dwarfs is T_eff ≈ 2900 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Observational study of interacting binary stars

We present a progress report on the results obtained from photometric and spectroscopic observations of the interacting binary stars SW Cyg, RR Dra, Y Leo, and SW Lyn in our Galaxy. Analogous studies could be eventually carried out for interacting binaries in the Local Group galaxies. From this study we note the significant Hα line profile variations in spectra of SW Cyg taken at two different orbital phases.     

Isotope spectroscopy

The measurement of isotopic ratios provides a privileged insight both into nucleosynthesis and into the mechanisms operating in stellar envelopes, such as gravitational settling. In this article, we give a few examples of how isotopic ratios can be determined from high‐resolution, high‐quality stellar spectra. We consider examples of the lightest elements, H and He, for which the isotopic shifts are very large and easily measurable, and examples of heavier elements for which the determination of isotopic ratios is more difficult. The presence of ⁶Li in the stellar atmospheres causes a subtle extra depression in the red wing of the ⁷Li 670.7 nm doublet which can only be detected in spectra of the highest quality. But even with the best spectra, the derived ⁶Li abundance can only be as good as the synthetic spectra used for their interpretation. It is now known that 3D non‐LTE modelling of the lithium spectral line profiles is necessary to account properly for the intrinsic line asymmetry, which is produced by convective flows in the atmospheres of cool stars, and can mimic the presence of ⁶Li. We also discuss briefly the case of the carbon isotopic ratio in metal‐poor stars, and provide a new determination of the nickel isotopic ratios in the solar atmosphere. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical composition of a sample of bright solar‐metallicity stars

We present a detailed analysis of seven young stars observed with the spectrograph SOPHIE at the Observatoire de Haute‐Provence for which the chemical composition was incomplete or absent in the literature. For five stars, we derived the stellar parameters and chemical compositions using our automatic pipeline optimized for F, G, and K stars, while for the other two stars with high rotational velocity, we derived the stellar parameters by using other information (parallax), and performed a line‐by‐line analysis. Chromospheric emission‐line fluxes from Caii are obtained for all targets. The stellar parameters we derive are generally in good agreement with what is available in the literature. We provide a chemical analysis of two of the stars for the first time. The star HIP 80124 shows a strong Li feature at 670.8 nm implying a high lithium abundance. Its chemical pattern is not consistent with it being a solar sibling, as has been suggested. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Circumstellar molecular envelopes of AGB and post-AGB objects

The line Li I 6708 has been sought in a sample of spectra of slow-rotating Ap stars, selected on the basis of their richness in metallic lines. The problem of the determination of the atmospheric parameters T _eff and log g from colour indices is discussed. More than 20 per cent of the stars show an absorption line at 6708, but the presence of this feature, among Ap stars, appears to be erratic. Its identification as Li I is discussed and the parameters needed to obtain meaningful lithium abundances are examined.Based on observations collected at the European Southern Observatory (ESO), La Silla, Chile and at the Observatoire de Haute Provence (OHP), Saint Michel l'Observatoire, France.     

Oxygen abundance in giant H II galaxies

A sample of 93 emission-line high luminosity galaxies from the Sloan Digital Sky Survey (SDSS) has been investigated. Line intensities have been measured in 116 SDSS spectra. Oxygen abundance has been determined in the studied galaxies. Since the auroral line of twice ionized oxygen [O III] λ 436.3 nm cannot be detected in the spectra of the sample, the intensity ratio of nebular to auroral lines needed to determine the electron temperature is calculated using the ff-relation. The oxygen abundances obtained in SDSS high luminosity galaxies are 0.2–0.5 dex lower than the maximum attainable value. This is caused by the fact that the sample includes only the gas-rich galaxies in which intense bursts of star formation occur. The equivalent number of O7 V stars which are responsible for excitation of luminescent H II regions in the studied sample is two or three orders of magnitude more than the number of stars which cause the luminescence of the brightest H II regions in nearby galaxies, and it exceeds by one order of magnitude the number of stars which cause gas in SBS 0335-052 E to glow.     

An atlas of ground UV spectra of selected stars

We present a spectral atlas of 4 B and A stars containing spectra in a poorly studied spectral range of 305–452 nm. The atlas is based on high resolution (R=60 000) spectra obtained with the 6 meter telescope (SAO, Russia) combined with the NES-spectrograph. The procedure of spectral lines identification and compilation of the atlas is discussed in detail. Using the spectral data we thoroughly investigated the velocity field in expanding atmospheres and envelopes of hot evolved stars β Ori, α Cyg and supergiant KS Per with the extreme hydrogen deficiency. The complete atlas and list of the identified spectral lines will be available via the astronomical database SIMBAD.     

Detection of lithium in the spectrum of the symbiotic Mira star V407 Cygni

We detected the resonance lithium doublet, ⁷LiI λ6708, in the spectra of the symbiotic Mira V407 Cyg (P≈763^d) obtained with a resolution R = λ/Δλ ≈ 18 500. The line equivalent width is ～0.34 Å. The presence of lithium in the atmosphere of the Mira, which, judging by its period, appreciably ascended the asymptotic giant branch (AGB), can be explained by the penetration of its convective envelope into the hot-bottom-burning (HBB) hydrogen-shell source. At the same time, the spectrum of V407 Cyg does not reveal the ZrO λ5551, 6474 absorption bands, which are used to classify S-type stars from low-resolution spectra. We found only weak ZrO λ5718, 6412 bands, which are, however, invisible in low-resolution spectra. Thus, the Mira star V407 Cyg should be classified as being of the spectral type M. In general, the spectrum of V407 Cyg is similar to the spectrum of the red giant in the symbiotic star CH Cyg, but the latter exhibits no lithium lines. The switch-on of the HBB process without any significant enrichment of the atmosphere of an AGB star with s-process elements implies that the third dredge-up is not efficient for some of these stars.