J/A+A/704/A283 HIP18606 and HIP111909 radial-velocity data (Jenkins+, 2025)
Sub-Jupiter gas giants orbiting giant stars uncovered using a Bayesian
framework.
Jenkins J.S., Jones M.I., Vines J.I., Rubenstein R.I., Pena Rojas P.A.,
Wittenmyer R., Brahm R., Tala Pinto M., Carson J.
<Astron. Astrophys. 704, A283 (2025)>
=2025A&A...704A.283J 2025A&A...704A.283J (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Exoplanets ; Radial velocities ; Optical
Keywords: planets and satellites: detection -
planets and satellites: dynamical evolution and stability -
planets and satellites: formation -
planets and satellites: fundamental parameters -
planets and satellites: gaseous planets - planet-star interactions
Abstract:
Giant stars have been shown to be rich hunting grounds for those
aiming to detect giant planets orbiting beyond ∼0.5AU. Here we present
two planetary systems around bright giant stars, found by combining
the radial-velocity (RV) measurements from the EXPRESS and PPPS
projects, and using a Bayesian framework. HIP18606 is a naked-eye
(V=5.8mag) K0III star and is found to host a planet with an orbital
period of ∼675 days, a minimum mass (msini) of 0.8MJ, and a circular
orbit. HIP111909 is a bright (V=7.4mag) K1III star, and hosts two
giant planets on circular orbits with minimum masses of msini=1.2MJ
and msini=0.8MJ, and orbital periods of ∼490d and ∼890d, for planets b
and c respectively, strikingly close to the 5:3 orbital period ratio.
Analysis of 11 known giant star planetary systems arrive at broadly
similar parameters to those published, whilst adding a further two new
worlds orbiting these stars. With these new discoveries, we have found
a total of 13 planetary systems (including three multiple systems)
within the 37 giant stars that comprise the EXPRESS and PPPS common
sample. Periodogram analyses of stellar activity indicators present
possible peaks at frequencies close to proposed Doppler signals in at
least two planetary systems, HIP24275 and HIP90988, calling for more
long-term activity studies of giant stars. Even disregarding these
possible false-positives, extrapolation leads to a fraction of 25-30%
of low-luminosity giant stars hosting planets. We find the
mass-function exponentially rises towards the lowest planetary masses,
however there exists a ∼93% probability that a second population of
giant planets with minimum masses between 4-5 MJ is present, worlds
that could have formed by the gravitational collapse of fragmenting
proto-planetary disks. Finally, our noise modelling reveals a lack of
statistical evidence for the presence of correlated noise at these RV
precision levels, meaning white noise models are favoured for such
data sets. However, different eccentricity priors can lead to
significantly different results, advocating for model grid analyses
like those applied here to be regularly performed. By using our
Bayesian analysis technique to better sample the posteriors, we are
helping to extend the planetary mass parameter space to below 1MJ,
building the first vanguard of a new population of super-Saturns
orbiting giant stars.
Description:
Radial-velocity (RV) and stellar activity timeseries data for two of
the new planetary systems discovered in this work, HIP18606 and
HIP111909. For both of these stars we present the Barycentric Julian
Dates, the RVs, the RV uncertainties, the Bisector Inverse Slope
measurements, the calculated S-indices, and the instrument used in the
measurement.
Objects:
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RA (2000) DE Designation(s)
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03 58 52.39 -05 28 11.8 HIP 18606 = HR 1232
22 40 07.18 -49 35 53.7 HIP 111909 = HD 214573
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 53 54 HIP 18606 timeseries data
table2.dat 53 52 HIP 111909 timeseries data
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Byte-by-byte Description of file: table1.dat table2.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d BJD Barycentric Julian Date
15- 20 F6.2 m/s RV Radial velocity
22- 26 F5.2 m/s e_RV Radial velocity uncertainty
28- 33 F6.1 m/s BIS ?=- Bisector Inverse Slope (1)
36- 41 F6.4 --- Sind ?=- S-index (1)
43- 53 A11 --- Inst Instrument
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Note (1): Columns with a '-' indicate no values present for that parameter.
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Acknowledgements:
James Jenkins, james.jenkins(at)mail.udp.cl
(End) James S. Jenkins [UDP, Chile], Patricia Vannier [CDS] 25-Nov-2025