The sdB pulsating star V391 Peg and its putative giant planet revisited after 13 years of timeseries photometric data
Abstract
V391 Peg (alias HS 2201+2610) is a subdwarf B (sdB) pulsating star that shows both p and gmodes. By studying the arrival times of the pmode maxima and minima through the OC method, in a previous article the presence of a planet was inferred with an orbital period of 3.2 years and a minimum mass of 3.2 M_{Jup}. Here we present an updated OC analysis using a larger data set of 1066 h of photometric time series ( 2.5× larger in terms of the number of data points), which covers the period between 1999 and 2012 (compared with 19992006 of the previous analysis). Up to the end of 2008, the new OC diagram of the main pulsation frequency (f_{1}) is compatible with (and improves) the previous twocomponent solution representing the longterm variation of the pulsation period (parabolic component) and the giant planet (sine wave component). Since 2009, the OC trend of f_{1} changes, and the time derivative of the pulsation period (p^{.}) 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 OC diagram of the secondary pulsation frequency (f_{2}) continues to show two components (parabola and sine wave), like in the previous analysis. Various solutions are proposed to fit the OC diagrams of f_{1} and f_{2}, but in all of them, the sinusoidal components of f_{1} and f_{2} 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 analyzed. 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^{.} for f_{1} and f_{2}: using only the data up to the end of 2008, we obtain p^{.}_{1} = (1.34 ± 0.04) × 10^{12} and p^{.}_{2} = (1.62 ± 0.22) × 10^{12}. The longterm variation of the two main pulsation periods (and the change of sign of p^{.}_{1}) is visible also in direct measurements made over several years. The absence of peaks near f_{1} in the Fourier transform and the secondary peak close to f_{2} confirm a previous identification as l = 0 and l = 1, respectively, and suggest a stellar rotation period of about 40 days. The new data allow constraining the main gmode pulsation periods of the star.
The complete set of data shown in Fig. 1 is only available at the CDS via anonymous ftp to http://cdsarc.ustrasbg.fr (http://130.79.128.5) or via http://cdsarc.ustrasbg.fr/vizbin/qcat?J/A+A/611/A85Based on observations obtained at the following observatories: WHT 4.2m, TNG 3.6m, Calar Alto 2.2m, NOT 2.5m, Loiano 1.5m, LOAO 1.0m, MDM 1.3m, Moletai 1.6m, MONETNorth 1.2m, Piszkéstető 1.0m, Mercator 1.2m, Wise 1.0m, Lulin 1.0m, Baker 0.6m.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 April 2018
 DOI:
 10.1051/00046361/201731473
 arXiv:
 arXiv:1711.10942
 Bibcode:
 2018A&A...611A..85S
 Keywords:

 stars: horizontalbranch;
 stars: oscillations;
 asteroseismology;
 stars: individual: V391 Peg;
 planets and satellites: detection;
 planets and satellites: individual: V391 Peg b;
 Astrophysics  Solar and Stellar Astrophysics;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 13 pages, 11 figures, accepted for publication in Astronomy and Astrophysics