Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005a%26a...438..973r&link_type=abstract
Astronomy and Astrophysics, Volume 438, Issue 3, August II 2005, pp.973-985
Astronomy and Astrophysics
Astrophysics
40
Stars: Atmospheres, Stars: Chemically Peculiar, Stars: Abundances, Stars: Individual: Hd 204411
Scientific paper
We present results of an abundance and stratification analysis of the weakly magnetic chemically peculiar star HD 204411 based on the echelle spectrum obtained with the high resolution spectrograph at the 3.55-m Telescopio Nazionale Galileo at the Observatorio del Roque de los Muchachos (La Palma, Spain). Atmospheric parameters obtained from the spectroscopy and spectrophotometry together with the Hipparcos parallax show that this star has already left the Main Sequence band. The upper limit for the surface magnetic field derived from the differential broadening of the spectral lines with different magnetic sensitivity is 750 G, which agrees with the recent detection of the weak effective magnetic field in this star. The best fit to the observed spectral line profiles was obtained with a combination of the rotational velocity v_e sin i = 5.4 km s-1 and the radial-tangential macroturbulence of 4.8 km s-1. The average abundances of HD 204411 are typical for an Ap star of the Cr-type: C and O are deficient, Cr and Fe are strongly overabundant. Sr, Y, Zr and the rare-earths, which usually have large overabundances in cool Ap stars with strong magnetic fields, are either normal (Y, Ce) or only +0.5 dex overabundant in the weakly magnetic star HD 204411. The chemical stratification analysis was performed for 5 elements, Mg, Si, Ca, Cr and Fe. Si, Ca and Fe show a tendency to be concentrated below logτ5000=-1, while for Mg we found marginal evidence for concentration in the upper atmosphere. This behaviour of Mg may be an artifact caused by the limited sample of spectral lines and poor atomic data available for the Mg II lines used in our analysis. Chromium, the most anomalous Fe-peak element, does not show significant abundance gradients in the line-forming region.
Kochukhov Oleg
Leone Francesco
Ryabchikova Tanya
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