Journal Article

The fundamental parameters of the roAp star α Circini*

H. Bruntt, J. R. North, M. Cunha, I. M. Brandão, V. G. Elkin, D. W. Kurtz, J. Davis, T. R. Bedding, A. P. Jacob, S. M. Owens, J. G. Robertson, W. J. Tango, J. F. Gameiro, M. J. Ireland and P. G. Tuthill

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 386, issue 4, pages 2039-2046
Published in print June 2008 | ISSN: 0035-8711
Published online April 2008 | e-ISSN: 1365-2966 | DOI:
The fundamental parameters of the roAp star α Circini*

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We have used the Sydney University Stellar Interferometer to measure the angular diameter of α Cir. This is the first detailed interferometric study of a rapidly oscillating A (roAp) star, α Cir being the brightest member of its class. We used the new and more accurate Hipparcos parallax to determine the radius to be 1.967 ± 0.066 R. We have constrained the bolometric flux from calibrated spectra to determine an effective temperature of 7420 ± 170 K. This is the first direct determination of the temperature of an roAp star. Our temperature is at the low end of previous estimates, which span over 1000 K and were based on either photometric indices or spectroscopic methods. In addition, we have analysed two high-quality spectra of α Cir, obtained at different rotational phases and we find evidence for the presence of spots. In both spectra we find nearly solar abundances of C, O, Si, Ca and Fe, high abundance of Cr and Mn, while Co, Y, Nd and Eu are overabundant by about 1 dex. The results reported here provide important observational constraints for future studies of the atmospheric structure and pulsation of α Cir.

Keywords: techniques: interferometric; stars: chemically peculiar; stars: fundamental parameters; stars: individual: α Cir

Journal Article.  6857 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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