50 research outputs found
Multi-element Doppler imaging of the CP2 star HD 3980
In atmospheres of magnetic main-sequence stars, the diffusion of chemical
elements leads to a number of observed anomalies, such as abundance spots
across the stellar surface. The aim of this study was to derive a detailed
picture of the surface abundance distribution of the magnetic chemically
peculiar star HD 3980. Based on high-resolution, phase-resolved spectroscopic
observations of the magnetic A-type star HD 3980, the inhomogeneous surface
distribution of 13 chemical elements (Li, O, Si, Ca, Cr, Mn, Fe, La, Ce, Pr,
Nd, Eu, and Gd) has been reconstructed. The INVERS12 code was used to invert
the rotational variability in line profiles to elemental surface distributions.
Assuming a centered, dominantly dipolar magnetic field configuration, we find
that Li, O, Mg, Pr, and Nd are mainly concentrated in the area of the magnetic
poles and depleted in the regions around the magnetic equator. The high
abundance spots of Si, La, Ce, Eu, and Gd are located between the magnetic
poles and the magnetic equator. Except for La, which is clearly depleted in the
area of the magnetic poles, no obvious correlation with the magnetic field has
been found for these elements otherwise. Ca, Cr, and Fe appear enhanced along
the rotational equator and the area around the magnetic poles. The intersection
between the magnetic and the rotational equator constitutes an exception,
especially for Ca and Cr, which are depleted in that region. No obvious
correlation between the theoretically predicted abundance patterns and those
determined in this study could be found. This can be attributed to a lack of
up-to-date theoretical models, especially for rare earth elements.Comment: 1o pages, accepted by A&
Lithium and its isotopic ratio 6Li/7Li in the atmospheres of some sharp-lined roAp star
The lines of lithium at 6708 A, and 6103 A, are analyzed in high resolution
spectra of some sharp-lined and slowly rotating roAp stars. Three spectral
synthesis codes - STARSP, ZEEMAN2 and SYNTHM were used. New lines of the rare
earth elements from the DREAM database, and lines calculated on the basis of
the NIST energy levels were included. Magnetic splitting and other line
broadening processes were taken into account. Enhanced abundances of lithium in
the atmospheres of the stars studied are obtained for both the lithium lines.
High estimates of 6Li/7Li ratio (0.2 -- 0.5) for the studied star can be
explained by Galactic Cosmic Ray (GCR) production through the spallation
reactions and the preservation of the original Li and Li by the strong
magnetic fields.Comment: 5 pages, 2*5 figs, submitted for IAUS #224 Proceeding
Lithium and its isotopic ratio ⁶Li/⁷Li in the atmospheres of sharp-lined roAp stars γ Equulei and HD 166473
The lithium lines at 6708 Å for two sharp-lined roAp stars γ Equ and HD 166473 and at 6103 Å for γ Equ were analyzed in high resolution spectra. Three spectral synthesis codes – STARSP, ZEEMAN2, and SYNTHM – were used. New lines of the rare-earth elements from the DREAM database and lines calculated on the basis of the NIST energy levels were included. Magnetic splitting and other line broadening processes were taken into account. Enhanced abundances of lithium in the atmospheres of the stars and high estimates of ⁶Li/⁷Li ratio (0.2 ÷ 0.5) can be explained by the Galactic Cosmic Ray (GCR) production due to spallation reactions and the preservation of original ⁶Li and ⁷Li by strong magnetic fields
Photometry of ET Andromedae and pulsation of HD 219891
ET And is a binary system with a B9p(Si) star as the main component. We report on the photometric observing campaigns in 1988, 1989 and 1994 which confirmed the rotation period of 1(.)(d)618875 for ET And while refuting other published values. Furthermore, the controversial issue of pulsational stability of ET And is resolved since we have discovered pulsation for HD 219891, which was the main comparison star and sometimes exclusively used. The frequency of 10.0816 d(-1), a semi-amplitude of 2.5 mmag, T(eff) and M(v) suggest this comparison star to be a delta Scuti variable close to the blue border of the instability strip. The pulsational stability of ET And could be clearly established and hence no need exists to derive new driving mechanisms for stars between the classical instability strip and the region of slowly pulsating B-type (SPB) stars