211 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
Evolutionary history of four binary blue stragglers from the globular clusters \omega Cen, M55, 47 Tuc and NGC 6752
Context. Origin and evolution of blue stragglers in globular clusters is
still a matter of debate. Aims. The aim of the present investigation is to
reproduce the evolutionary history of four binary blue stragglers in four
different clusters, for which precise values of global parameters are known.
Methods. Using the model for cool close binary evolution, developed by one of
us (KS), progenitors of all investigated binaries were found and their
parameters evolved into the presently observed values. Results. The results
show that the progenitors of the binary blue stragglers are cool close binaries
with period of a few days, which transform into stragglers by rejuvenation of
the initially less massive component by mass transfer from its more massive
companion overflowing the inner critical Roche surface. The parameters of V209
from \omega Cen indicate that the binary is substantially enriched in helium.
This is an independent and strong evidence for the existence of the helium rich
subpopulation in this cluster.Comment: Accepted by Astronomy and Astrophysic
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