201 research outputs found
Detection of high-degree prograde sectoral mode sequences in the A-star KIC 8054146?
This paper examines the 46 frequencies found in the Delta Sct star KIC
8054146 involving a frequency spacing of exactly 2.814 c/d (32.57 microHz),
which is also a dominant low-frequency peak near or equal to the rotational
frequency. These 46 frequencies range up to 146 c/d. Three years of Kepler data
reveal distinct sequences of these equidistantly spaced frequencies, including
the basic sequence and side lobes associated with other dominant modes (i.e.,
small amplitude modulations). The amplitudes of the basic sequence show a
high-low pattern. The basic sequence follows the equation fm = 2.8519 + m *
2.81421 c/d with m ranging from 25 to 35. The zero-point offset and the lack of
low-order harmonics eliminate an interpretation in terms of a Fourier series of
a non-sinusoidal light curve. The exactness of the spacing eliminates
high-order asymptotic pulsation. The frequency pattern is not compatible with
simple hypotheses involving single or multiple spots, even with differential
rotation. The basic high-frequency sequence is interpreted in terms of prograde
sectoral modes. These can be marginally unstable, while their corresponding
low-degree counterparts are stable due to stronger damping. The measured
projected rotation velocity (300 km/s) indicates that the star rotates with
app. 70% of the Keplerian break-up velocity. This suggests a near equator-on
view. We qualitatively examine the visibility of prograde sectoral high-degree
g-modes in integrated photometric light in such a geometrical configuration and
find that prograde sectoral modes can reproduce the frequencies and the
odd-even amplitude pattern of the high-frequency sequence
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