Abundances and chemical stratification analysis in the atmosphere of Cr-type Ap star HD 204411

¹ Institute for Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 119017 Moscow, Russia e-mail: ryabchik@inasan.rssi.ru
² Institute for Astronomy, University of Vienna, Türkenschanzstraße 17, 1180 Vienna, Austria e-mail: last_name@astro.univie.ac.at;oleg@astro.uu.se
³ INAF - Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy e-mail: fleone@ct.astro.it

Received: 12 September 2004
Accepted: 31 March 2005

Abstract

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  = 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 , 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  lines used in our analysis. Chromium, the most anomalous Fe-peak element, does not show significant abundance gradients in the line-forming region.