Title: The sdB pulsating star V391 Peg and its putative giant planet revisited after 13 years of time-series photometric data,
Abstract: V391 Peg (alias HS2201+2610) is a subdwarf B (sdB) pulsating star that shows
both p- and g-modes. By studying the arrival times of the p-mode maxima and
minima through the O-C method, in a previous article the presence of a planet
was inferred with an orbital period of 3.2 yr and a minimum mass of 3.2 M_Jup.
Here we present an updated O-C analysis using a larger data set of 1066 hours
of photometric time series (~2.5x larger in terms of the number of data
points), which covers the period between 1999 and 2012 (compared with 1999-2006
of the previous analysis). Up to the end of 2008, the new O-C diagram of the
main pulsation frequency (f1) is compatible with (and improves) the previous
two-component solution representing the long-term variation of the pulsation
period (parabolic component) and the giant planet (sine wave component). Since
2009, the O-C trend of f1 changes, and the time derivative of the pulsation
period (p_dot) passes from positive to negative; the reason of this change of
regime is not clear and could be related to nonlinear interactions between
different pulsation modes. With the new data, the O-C diagram of the secondary
pulsation frequency (f2) continues to show two components (parabola and sine
wave), like in the previous analysis. Various solutions are proposed to fit the
O-C diagrams of f1 and f2, but in all of them, the sinusoidal components of f1
and f2 differ or at least agree less well than before. The nice agreement found
previously was a coincidence due to various small effects that are carefully
analysed. Now, with a larger dataset, the presence of a planet is more
uncertain and would require confirmation with an independent method. The new
data allow us to improve the measurement of p_dot for f1 and f2: using only the
data up to the end of 2008, we obtain p_dot_1=(1.34+-0.04)x10**-12 and
p_dot_2=(1.62+-0.22)x10**-12 ...