Asteroseismic analysis of the roAp star alpha Circini: 84 days of high-precision photometry from the WIRE satellite - Astrophysics > Solar and Stellar AstrophysicsReport as inadecuate




Asteroseismic analysis of the roAp star alpha Circini: 84 days of high-precision photometry from the WIRE satellite - Astrophysics > Solar and Stellar Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: We present a detailed study of the pulsation of alpha Circini, the brightestof the rapidly oscillating Ap stars. We have obtained 84 days of high-precisionphotometry from four runs with the star tracker on the WIRE satellite.Simultaneously, we collected ground-based Johnson B observations on 16 nightsat the South African Astronomical Observatory. In addition to the dominantoscillation mode at 2442 microHz, we detect two new modes that liesymmetrically around the principal mode to form a triplet. The averageseparation between these modes is 30.173+-0.004 microHz and they are nearlyequidistant with the separations differing by only 3.9 nHz. We compare theobserved frequencies with theoretical pulsation models based on constraintsfrom the recently determined interferometric radius and effective temperature,and the recently updated Hipparcos parallax. We show that the theoretical largeseparations for models of alpha Cir with global parameters within the 1-sigmaobservational uncertainties vary between 59 and 65 microHz. This is consistentwith the large separation being twice the observed value, indicating that thethree main modes are of alternating even and odd degrees. The frequencydifferences in the triplet are significantly smaller than those predicted fromour models, for all possible combinations of mode degrees, and may indicatethat the effects of magnetic perturbations need to be taken into account. TheWIRE light curves are modulated by a double wave with a period of 4.479 days,and a peak-to-peak amplitude of 4 mmag. This variation is due to the rotationof the star and is a new discovery, made possible by the high precision of theWIRE photometry. The rotational modulation confirms an earlier indirectdetermination of the rotation period.



Author: H. Bruntt, D. W. Kurtz, M. S. Cunha, I. M. Brandao, G. Handler, T. R. Bedding, T. Medupe, D. L. Buzasi, D. Mashigo, I. Zhang, F.

Source: https://arxiv.org/



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