Precise radial velocities of giant stars. XII. Evidence against the proposed planet Aldebaran b. (arXiv:1903.09157v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Reichert_K/0/1/0/all/0/1">Katja Reichert</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reffert_S/0/1/0/all/0/1">Sabine Reffert</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stock_S/0/1/0/all/0/1">Stephan Stock</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Trifonov_T/0/1/0/all/0/1">Trifon Trifonov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Quirrenbach_A/0/1/0/all/0/1">Andreas Quirrenbach</a>
Radial-velocity variations of the K giant star Aldebaran ($alpha$ Tau) were
first reported in the early 1990s. After subsequent analyses, the
radial-velocity variability with a period of $sim 629,mathrm{d}$ has
recently been interpreted as caused by a planet of several Jovian masses. We
want to further investigate the hypothesis of an extrasolar planet around
Aldebaran. We combine 165 new radial-velocity measurements from Lick
Observatory with seven already published data sets comprising 373
radial-velocity measurements. We perform statistical analyses and investigate
whether a Keplerian model properly fits the radial velocities. We also perform
a dynamical stability analysis for a possible two-planet solution. As best
Keplerian fit to the combined radial-velocity data we obtain an orbit for the
hypothetical planet with a smaller period ($P=607,mathrm{d}$) and a larger
eccentricity ($e=0.33 pm 0.04$) than the previously proposed one. However, the
residual scatter around that fit is still large, with a standard deviation of
$117,mathrm{ms}^{-1}$. In 2006/2007, the statistical power of the $sim
620,mathrm{d}$ period showed a temporary but significant decrease. Plotting
the growth of power in reverse chronological order reveals that a period around
$620,mathrm{d}$ is clearly present in the newest data but not in the data
taken before $sim$ 2006. Furthermore, an apparent phase shift between
radial-velocity data and orbital solution is observable at certain times. A
two-planet Keplerian fit matches the data considerably better than a
single-planet solution, but poses severe dynamical stability issues. The
radial-velocity data from Lick Observatory do not further support but in fact
weaken the hypothesis of a substellar companion around Aldebaran. Oscillatory
convective modes might be a plausible alternative explanation of the observed
radial-velocity variations.
Radial-velocity variations of the K giant star Aldebaran ($alpha$ Tau) were
first reported in the early 1990s. After subsequent analyses, the
radial-velocity variability with a period of $sim 629,mathrm{d}$ has
recently been interpreted as caused by a planet of several Jovian masses. We
want to further investigate the hypothesis of an extrasolar planet around
Aldebaran. We combine 165 new radial-velocity measurements from Lick
Observatory with seven already published data sets comprising 373
radial-velocity measurements. We perform statistical analyses and investigate
whether a Keplerian model properly fits the radial velocities. We also perform
a dynamical stability analysis for a possible two-planet solution. As best
Keplerian fit to the combined radial-velocity data we obtain an orbit for the
hypothetical planet with a smaller period ($P=607,mathrm{d}$) and a larger
eccentricity ($e=0.33 pm 0.04$) than the previously proposed one. However, the
residual scatter around that fit is still large, with a standard deviation of
$117,mathrm{ms}^{-1}$. In 2006/2007, the statistical power of the $sim
620,mathrm{d}$ period showed a temporary but significant decrease. Plotting
the growth of power in reverse chronological order reveals that a period around
$620,mathrm{d}$ is clearly present in the newest data but not in the data
taken before $sim$ 2006. Furthermore, an apparent phase shift between
radial-velocity data and orbital solution is observable at certain times. A
two-planet Keplerian fit matches the data considerably better than a
single-planet solution, but poses severe dynamical stability issues. The
radial-velocity data from Lick Observatory do not further support but in fact
weaken the hypothesis of a substellar companion around Aldebaran. Oscillatory
convective modes might be a plausible alternative explanation of the observed
radial-velocity variations.
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