J/MNRAS/503/1248 HD 13808 HARPS radial velocities (Ahrer+, 2021)
The HARPS search for southern extra-solar planets.
XLV. Two Neptune mass planets orbiting HD 13808:
a study of stellar activity modelling's impact on planet detection.
Ahrer E., Queloz D., Rajpaul V.M., Segransan D., Bouchy F., Hall R.,
Handley W., Lovis C., Mayor M., Mortier A., Pepe F., Thompson S.,
Udry S., Unger N.
<Mon. Not. R. Astron. Soc. 503, 1248-1263 (2021)>
=2021MNRAS.503.1248A 2021MNRAS.503.1248A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities
Keywords: methods: data analysis - methods: statistical -
techniques: radial velocities - stars: activity -
stars: individual: HD 13808
Abstract:
We present a comprehensive analysis of 10 years of HARPS radial
velocities of the K2V dwarf star HD13808, which has previously been
reported to host two unconfirmed planet candidates. We use the
state-of-the-art nested sampling algorithm PolyChord to compare a wide
variety of stellar activity models, including simple models exploiting
linear correlations between RVs and stellar activity indicators,
harmonic models for the activity signals, and a more sophisticated
Gaussian process regression model. We show that the use of
overly-simplistic stellar activity models that are not well-motivated
physically can lead to spurious `detections' of planetary signals that
are almost certainly not real. We also reveal some difficulties
inherent in parameter and model inference in cases where multiple
planetary signals may be present. Our study thus underlines the
importance both of exploring a variety of competing models and of
understanding the limitations and precision settings of one's sampling
algorithm. We also show that at least in the case of HD 13808, we
always arrive at consistent conclusions about two particular signals
present in the RV, regardless of the stellar activity model we adopt;
these two signals correspond to the previously-reported though
unconfirmed planet candidate signals. Given the robustness and
precision with which we can characterize these two signals, we deem
them secure planet detections. In particular, we find two planets
orbiting HD13808 at distances of 0.11, 0.26AU with periods of 14.2,
53.8d, and minimum masses of 11, 10 Earth masses.
Description:
Spectra of HD 13808 were measured with HARPS, a fibre-fed
spectrograph installed in a vacuum vessel, mounted on the 3.6m ESO
telescope of La Silla in Chile (Mayor et al., 2003Msngr.114...20M 2003Msngr.114...20M).
Observations were made using the most precise observing mode that
utilizes a simultaneous calibration by the ThAr calibration lamp. In
this configuration, HARPS achieves a long-term RV precision better
than 1m/s, allowing us to detect small stellar RV variations
of this order (Lovis et al., 2008, ASP Conf. Ser., 398, 455).
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
02 12 42.93 -53 44 38.0 HD 13808 = HIP 10301
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
hd13808.dat 120 246 HARPS radial velocities of the K2V dwarf star
HD 13808
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Byte-by-byte Description of file: hd13808.dat
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Bytes Format Units Label Explanations
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1- 18 F18.12 d Date Time in RJD (JD-2400000)
20- 31 F12.6 m/s RV Radial velocity
33- 40 F8.6 m/s e_RV Radial velocity error
42- 52 F11.6 m/s FWHM FWHM of CCF
54- 62 F9.6 m/s BIS Bisector span of the CCF
64- 72 F9.6 --- Cont Contrast of the CCF
74- 81 F8.6 --- SMW S index
83- 90 F8.6 --- e_SMW S index error
92-100 F9.6 --- RHK logR'HK
102-109 F8.6 --- e_RHK logR'HK error
111-120 F10.6 m/s BERV Barycentric Earth radial velocity
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Acknowledgements:
Eva-Maria Ahrer, eva-maria.ahrer(at)warwick.ac.uk
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(End) Patricia Vannier [CDS] 05-Feb-2021