Surface structure of the CoRoT CP2 target star HD 50773^*

T. Lüftinger¹, H.-E. Fröhlich², W. W. Weiss¹, P. Petit³, M. Aurière³, N. Nesvacil¹, M. Gruberbauer¹, D. Shulyak¹, E. Alecian⁴, A. Baglin⁴, F. Baudin⁵, C. Catala⁴, J.-F. Donati³, O. Kochukhov⁶, E. Michel^4,7, N. Piskunov⁶, T. Roudier³ and R. Samadi^4,7

¹ Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, 1180 Wien, Austria e-mail: lueftinger@astro.univie.ac.at
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
³ Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, France
⁴ Observatoire de Paris, LESIA, 5 place Jules Janssen, 92195 Meudon Cedex, France
⁵ Institut d'Astrophysique Spatiale, UMR8617, Université Paris X, Bât. 121, 91405 Orsay, France
⁶ Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
⁷ Université Pierre et Marie Curie, Université Denis Diderot, Pl. J. Janssen, 92195 Meudon, France

Received: 31 March 2009
Accepted: 27 October 2009

Abstract

Aims. We compare surface maps of the chemically peculiar star HD 50773 produced with a Bayesian technique and based on high quality CoRoT photometry with those derived from rotation phase resolved spectropolarimetry. The goal is to investigate the correlation of surface brightness with surface chemical abundance distribution and the stellar magnetic surface field.

Methods. The rotational period of the star was determined from a nearly 60 days long continuous light curve obtained during the initial run of CoRoT. Using a Bayesian approach to star-spot modelling, which in this work is applied for the first time for the photometric mapping of a CP star, we derived longitudes, latitudes and radii of four different spot areas. Additional parameters like stellar inclination and the spot's intensities were also determined. The CoRoT observations triggered an extensive ground-based spectroscopic and spectropolarimetric observing campaign and enabled us to obtain 19 different high resolution spectra in Stokes parameters I and V with NARVAL, ESPaDOnS, and SemelPol spectropolarimeters. Doppler and Magnetic Doppler imaging techniques allowed us to derive the magnetic field geometry of the star and the surface abundance distributions of Mg, Si, Ca, Ti, Cr, Fe, Ni, Y, and Cu.

Results. We find a dominant dipolar structure of the surface magnetic field. The CoRoT light curve variations and abundances of most elements mapped are correlated with the aforementioned geometry: Cr, Fe, and Si are enhanced around the magnetic poles and coincide with the bright regions on the surface of HD 50773 as predicted by our light curve synthesis and confirmed by photometric imaging.