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, P. G. Tuthill

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)2039-2046
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - Jun 2008
Externally publishedYes

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