J/A+A/664/A64 GJ 832 stellar activity (Gorrini+, 2022)
Detailed stellar activity analysis and modelling of GJ 832.
Reassessment of the putative habitable zone planet GJ 832c.
Gorrini P., Astudillo-Defru N., Dreizler S., Damasso M., Diaz R.F.,
Bonfils X., Jeffers S.V., Barnes J.R., Del Sordo F., Almenara J.-M.,
Artigau E., Bouchy F., Charbonneau D., Delfosse X., Doyon R., Figueira P.,
Forveille T., Haswell C.A., Lopez-Gonzalez M.J., Melo C., Mennickent R.E.,
Gaisne G., Morales N., Murgas F., Pepe F., Rodriguez E., Santos N.C.,
Tal-Or L., Tsapras Y., Udry S.
<Astron. Astrophys. 664, A64 (2022)>
=2022A&A...664A..64G 2022A&A...664A..64G (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Photometry, UBV ;
Radial velocities ; Spectroscopy
Keywords: stars: activity - stars: individual: GJ 832 - planetary systems -
techniques: radial velocities - techniques: photometric
Abstract:
Gliese-832 (GJ 832) is an M2V star hosting a massive planet on a
decade-long orbit, GJ 832b, discovered by radial velocity (RV). Later,
a super Earth or mini-Neptune orbiting within the stellar habitable
zone was reported (GJ 832c). The recently determined stellar rotation
period (45.7±9.3 days) is close to the orbital period of putative
planet c (35.68±0.03 days).
We aim to confirm or dismiss the planetary nature of the RV signature
attributed to GJ 832c, by adding 119 new RV data points, new
photometric data, and an analysis of the spectroscopic stellar
activity indicators. Additionally, we update the orbital parameters of
the planetary system and search for additional signals.
We performed a frequency content analysis of the RVs to search for
periodic and stable signals. Radial velocity time series were modelled
with Keplerians and Gaussian process (GP) regressions alongside
activity indicators to subsequently compare them within a Bayesian
framework.
We updated the stellar rotational period of GJ 832 from activity
indicators, obtaining 37.5+1.41.5 days, improving the precision by
a factor of 6. The new photometric data are in agreement with this
value. We detected an RV signal near 18 days (FAP<4.6%), which is half
of the stellar rotation period. Two Keplerians alone fail at modelling
GJ 832b and a second planet with a 35-day orbital period. Moreover,
the Bayesian evidence from the GP analysis of the RV data with
simultaneous activity indices prefers a model without a second
Keplerian, therefore negating the existence of planet c.
Description:
This work makes use of data from HARPS, the University College London
Echelle Spectrograph (UCLES) , and the Planet Finding Spectrograph
(PFS). HARPS data are available as raw images and reduced spectra,
while we accessed UCLES and PFS data only as RV time series. We used a
total of 227 RV data points for GJ 832.
Objects:
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RA (2000) DE Designation(s)
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21 33 33.98 -49 00 32.4 GJ 832 = HD 204961
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
activity.dat 111 172 Activity indices of GJ 832 from HARPS
spectrograph
ash2.dat 31 633 Photometric data of GJ 832 from ASH2 telescope
rv.dat 45 227 RV timeseries of GJ 832
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Byte-by-byte Description of file: activity.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Barycentric Julian date
16- 23 F8.6 --- Halpha H-alpha index
25- 32 F8.6 --- e_Halpha H-alpha index error
34- 41 F8.6 --- Hbeta H-beta index
43- 50 F8.6 --- e_Hbeta H-beta index error
52- 59 F8.6 --- Hgamma H-gamma index
61- 68 F8.6 --- e_Hgamma H-gamma index error
70- 77 F8.6 --- NaD NaD index
79- 86 F8.6 --- e_NaD NaD index error
88- 95 F8.6 --- S S index
97-104 F8.6 --- e_S S index error
106-111 A6 --- Inst Instrument's name
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Byte-by-byte Description of file: ash2.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d HJD Heliocentric Julian Date
16- 22 F7.4 mag Dmag Differential magnitude
24- 29 F6.4 mag e_Dmag Differential magnitude error
31 A1 --- Filter [BV] Filter
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Byte-by-byte Description of file: rv.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d JD Julian Date
17- 25 F9.3 m/s RV ? Radial velocity for HARPS and HARPS+ (1)
26- 31 F6.2 m/s dRV ? Relative radial velocity for PFS and UCLES
33- 37 F5.3 m/s e_RV Radial velocity error (for RV and dRV)
40- 45 A6 --- Inst Instrument's name (HARPS, HARPS+, PFS or UCLES)
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Note (1): To have relative velocities,
substract 13353.31 for HARPS and 13354.90 for HARPS+ data.
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Acknowledgements:
Paula Gorrini, paula.gorrini(at)uni-goettingen.de
(End) Patricia Vannier [CDS] 29-Jul-2022