A surface-brightness analysis of selected northern Cepheids

B. Csák1, E.J. Alfaro2, L.L. Kiss1
1 Department of Experimental Physics and Astronomical Observatory, University of Szeged, H-6720 Szeged, Dóm tér 9., Hungary
2 Instituto de Astrofísica de Andalucía, CSIC, P.O. Box 3004, E-18080, Spain

 

We present an analysis of new Strömgren photometric observations of ~30 northern Cepheids obtained at Sierra Nevada Observatory between 1998 and 2001. Our study concentrated on the application of the intermediate band approach to the surface-brightness method for Cepheid radii and distance determination as calibrated by Arellano Ferro & Rosenzweig (2000, MNRAS 315, 296). For this, we have performed the following steps:

  1. New periods and epochs of maxima were determined to take into account the slightly changing ephemerides.
  2. The interstellar reddenings were estimated with two independent calibrations taken from the literature.
  3. After collecting all available radial velocity measurements, we have calculated distances, radii, absolute magnitudes for the programme stars. The resulting period-radius and period-luminosity relations are in excellent agreement with those of published most recently.
  4. Since a number of target stars are members of open clusters and associations, we could compare cluster reddenings and distances with the Cepheid values. We found them to be in good agreement except for RU Sct. We suggest this to be caused by a bright blue companion that strongly affects the observed colour indices.

 
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