Bibcode
Kurtz, D. W.; Cunha, M. S.; Saio, H.; Bigot, L.; Balona, L. A.; Elkin, V. G.; Shibahashi, H.; Brandão, I. M.; Uytterhoeven, K.; Frandsen, S.; Frimann, S.; Hatzes, A.; Lueftinger, T.; Gruberbauer, M.; Kjeldsen, H.; Christensen-Dalsgaard, J.; Kawaler, S. D.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 414, Issue 3, pp. 2550-2566.
Advertised on:
7
2011
Citations
55
Refereed citations
42
Description
We have discovered a new rapidly oscillating Ap (roAp) star among the
Kepler mission target stars, KIC 10195926. This star shows two pulsation
modes with periods that are amongst the longest known for roAp stars at
17.1 and 18.1 min, indicating that the star is near the terminal-age
main sequence. The principal pulsation mode is an oblique dipole mode
that shows a rotationally split frequency septuplet that provides
information on the geometry of the mode. The secondary mode also appears
to be a dipole mode with a rotationally split triplet, but we are able
to show within the improved oblique pulsator model that these two modes
cannot have the same axis of pulsation. This is the first time for any
pulsating star that evidence has been found for separate pulsation axes
for different modes. The two modes are separated in frequency by 55
μHz, which we model as the large separation. The star is an
α2 CVn spotted magnetic variable that shows a complex
rotational light variation with a period of Prot= 5.684 59 d.
For the first time for any spotted magnetic star of the upper main
sequence, we find clear evidence of light variation with a period of
twice the rotation period, that is, a subharmonic frequency of
νrot/2. We propose that this and other subharmonics are
the first observed manifestation of torsional modes in an roAp star.
From high-resolution spectra, we determine Teff= 7400 K, log
g= 3.6 and v sin i= 21 km s-1. We have found a magnetic
pulsation model with fundamental parameters close to these values that
reproduces the rotational variations of the two obliquely pulsating
modes with different pulsation axes. The star shows overabundances of
the rare earth elements, but these are not as extreme as most other roAp
stars. The spectrum is variable with rotation, indicating surface
abundance patches.