J/A+A/684/A12 TOI-776 RVs and spectral activity (Fridlund+, 2024)
Planets observed with CHEOPS.
Two super-Earths orbiting the red dwarf star TOI-776.
Fridlund M., Georgieva I.Y., Bonfanti A., Alibert Y., Persson C.M.,
Gandolfi D., Beck M., Deline A., Hoyer S., Olofsson G., Wilson T.G.,
Barragan O., Fossati L., Mustill A.J., Brandeker A., Hatzes A.,
Floren H.-G., Simola U., Hooton M.J., Luque R., Sousa S.G., Egger J.A.,
Antoniadis-Karnavas A., Salmon S., Adibekyan V., Alonso R., Anglada G.,
Barczy T., Barrado Navascues D., Barros S.C., Baumjohann W., Beck T.,
Benz W., Bonfils X., Broeg C., Cabrera J., Charnoz S., Collier Cameron A.,
Csizmadia Sz., Davies M.B., Deeg H., Deleuil M., Delrez L.,
Demangeon O.D.S., Demory B.-O., Ehrenreich D., Erikson A., Esposito M.,
Fortier A., Gillon M., Guedel M., Heng K., Isaak K.G., Kiss L., Korth J.,
Laskar J., Lecavelier des Etangs A., Lendl M., Livingston J., Lovis C.,
Magrin D., Maxted P.F.L., Muresan A., Nascimbeni V., Ottensamer R.,
Pagano I., Palle E., Peter G., Piotto G., Pollacco D., Queloz D.,
Ragazzoni R., Rando N., Rauer H., Redfield S., Ribas I., Santos N.C.,
Scandariato G., Segransan D., Serrano L.M., Simon A.E., Smith A.M.S.,
Steller M., Szabo M.Gy., Thomas N., Udry S., Van Eylen V., Van Grootel V.,
Walton N.A.
<Astron. Astrophys. 684, A12 (2024)>
=2024A&A...684A..12F 2024A&A...684A..12F (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities ;
Spectroscopy ; Optical
Keywords: techniques: photometric - techniques: spectroscopic -
planets and satellites: detection -
planets and satellites: individual: TOI-776 b -
planets and satellites: individual: TOI-776 c -
stars: individual: LP 961-53
Abstract:
M-dwarf stars are the most common of potential exoplanet host stars in
the Galaxy. It is therefore very important to understand planetary
systems orbiting such stars and to determine the physical parameters
of such planets with high precision. Also with the launch of the James
Webb Space Telescope (JWST) the observation of atmospheric parameters
of planets orbiting these stars has begun. It is therefore required to
determine properties of potential targets.
Two planets around the red dwarf TOI-776 were detected by TESS. The
objective of our study was to use transit observations obtained by the
CHEOPS space mission to improve the current precision of the planetary
radii, as well as additional radial velocity (RV) data in order to
improve mass estimates of the two planets. Using these quantities, we
wanted to derive the bulk densities of those planets, improving the
precision in earlier results, and use this information to put them in
context of other exoplanetary systems involving very low mass stars.
Utilizing new transit data from the CHEOPS satellite and its
photometric telescope, we obtained very high precision planetary
transit measurements. Interpretation of these provides updated
planetary radii, along with other system parameters. A concurrent ESO
large observing program using the high precision spectrograph HARPS
has doubled the available radial velocity data. Calculating the power
spectrum of a number of stellar activity indices we update the
previously estimated stellar rotation period to a lower value.
The CHEOPS data provide precise transit depths of 909 and 1177ppm
translating into radii of Rb=1.798+0.078-0.077R⊕ and
Rc=2.047+0.081-0.078R⊕, respectively. Our interpretation
of the radial velocities and activity indicator time series data
estimates a stellar rotation period for this early Mdwarf of
∼21.1days. A further multi-dimensional Gaussian process approach
confirm this new estimate. By performing a Skew-Normal (SN) fit onto
the Cross Correlation Functions we extracted the RV data and the
activity indicators to estimate the planetary masses, obtaining
Mb=5.0+1.6+-1.6M⊕ and Mc=6.9+2.6-2.5M⊕.
We improve the precision in planetary radius for TOI-776 b and c by a
factor of more than two. Our data and modelling give us parameters of
both bodies consistent with mini-Neptunes, albeit with a relatively
high density. The stellar activity of TOI-776 is found to have
increased by a factor larger than 2 since the last set of
observations.
Description:
In order to increase the precision in the mass determinations, we
collected 35 additional RV data points with the HARPS spectrograph
(R=115000) mounted at the ESO 3.6m telescope (La Silla observatory,
Chile: LP 106.21TJ.001; P.I. D. Gandolfi).
With 35 new HARPS spectra, the resulting data set contains 64 HARPS
spectra in total.
Objects:
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RA (2000) DE Designation(s)
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11 54 18.39 -37 33 09.8 TOI-776 = TIC 306996324
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 104 64 Radial velocities and spectral activity
indicators measured from TNG/HARPS-N spectra
tablea2.dat 60 64 Radial velocities, SN hyperparameters and
detrended radial velocities
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 11 F11.6 d BJD Barycentric Julian date (TBD) (BJD-2450000)
13- 17 F5.2 m/s RVTERRA TERRA radial velocity
19- 22 F4.2 m/s e_RVTERRA TERRA radial velocity error
24- 29 F6.2 m/s RVSERVAL SERVAL radial velocity
31- 34 F4.2 m/s e_RVSERVAL SERVAL radial velocity error
36- 41 F6.2 m2/s2 dlW Differential line width
43- 46 F4.2 m2/s2 e_dlW Differential line width error
48- 53 F6.2 m/s2 CRX Chromatic index (in m/s2/Np)
55- 59 F5.2 m/s2 e_CRX Chromatic index error (in m/s2/Np)
61- 66 F6.4 --- S-index Mont-Wilson S index
68- 73 F6.4 --- e_S-index Mont-Wilson S index error
75- 80 F6.4 --- Ha Hα line index
82- 87 F6.4 --- NaD1 NaD1 line index
89- 94 F6.4 --- NaD2 NaD2 line index
96- 99 I4 s Texp Exposure time
101-104 F4.1 --- SNR Signal-to-noise ratio @550nm
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 11 F11.6 d BJD Barycentric Julian date (TBD) (BJD-2450000)
13- 19 F7.3 m/s Mean radial velocity (1)
21- 25 F5.3 m/s e_ Mean radial velocity error
27- 31 F5.3 km/s FWHM-SN Full width at Half Maximum (FWHMSN)
hyperparameter
33- 37 F5.3 % A Contrast (A) SN hyperparameter
39- 46 F8.5 --- gamma Skewness (γ) SN hyperparameter
48- 54 F7.3 m/s RVdet Detrended radial velocity
56- 60 F5.3 m/s e_RVdet Detrended radial velocity error which also
account for the jitter
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Note (1): Radial velocities as inferred from the SN fit onto the centred
CCFs.
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Acknowledgements:
Malcolm Fridlund, malcolm.fridlund(at)chalmers.se
(End) Patricia Vannier [CDS] 29-Jan-2024