J/A+A/705/A260 TOI-521 and TOI-912 RV datasets (Lacedelli+, 2026)
Sibling Sub-Neptunes Around Sibling M Dwarfs: TOI-521 and TOI-912.
Lacedelli G., Palle E., Luque R., Ikuta K., Tabernero H.M.,
Zapatero Osorio M.R., Almenara J.M., Pozuelos F.J., Jankowski D., Narita N.,
Fukui A., Nowak G., Hirano T., Ishikawa H.T., Kimura T., Hori Y.,
Collins K.A., Howell S.B., Jiang C., Murgas F., Osborn H.P.,
Astudillo-Defru N., Bonfils X., Charbonneau D., Fausnaugh M.,
Geraldia-Gonzalez S., Gozdziewski K., Guerra P., Hayashi Y., Hodapp K.,
Horne K., Isogai K., Jafariyazani M., Kagetani T., Kawai Y., Kawauchi K.,
Krishnamurthy V., Kotani T., Kudo T., Kurokawa T., Kuzuhara M., Mori M.,
Nishikawa J., Nugroho S.K., Omiya M., Schwarz R.P., Sefako R., Shporer A.,
Srdoc G., Teng H., Watanabe N.
<Astron. Astrophys. 705, A260 (2026)>
=2026A&A...705A.260L 2026A&A...705A.260L (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities ;
Optical
Keywords: planets and satellites: detection -
planets and satellites: composition -
planets and satellites: individual: TOI-521 -
planets and satellites: individual: TOI-912
Abstract:
Sub-Neptunes are absent in the Solar System, yet they are the most
common category of planets found in our Galaxy. This kind of planet
challenges the internal structure models and prompts investigation on
their formation and evolution, as well as pushing towards atmospheric
characterisation studies to break the degeneracy in their inner
composition. We report here the discovery and characterisation of new
sub-Neptunes orbiting two similar M dwarfs, TOI-521 (Teff=3544±100K,
V=14.7mag), and TOI-912 (Teff=3572±100K, V=12.7mag). Both stars host
a transiting planetary candidate identified by TESS and are part of
the THIRSTEE follow-up program, which aims at understanding the
sub-Neptune population through in-depth and precise characterisation
studies on a population level. We analysed TESS light curves,
ground-based photometry and high-precision ESPRESSO, HARPS and IRD
radial velocities to confirm the planetary nature of both candidates,
infer precise orbital and physical parameters of the planets and
investigate the presence of additional planets in the systems. The two
stars host nearly identical planets in terms of mass and radius.
TOI-521 hosts a transiting sub-Neptune in a 1.5-days orbit with radius
and mass of Rb=1.98±0.14R⊕ and Mb=5.3±1.0M⊕,
respectively. Moreover, we identified an additional candidate at
20.3-days, with a minimum mass of Mpsin(i)=10.7M⊕, currently
not detected to transit in our photometric dataset. Similarly, the
planet orbiting TOI-912 is a 4.7-d sub-Neptune with
Rb=1.93±0.13R⊕ and Mb=5.1±0.5M⊕.
Interestingly, TOI-912 b likely possesses an unusually high
eccentricity (e=0.58±0.02), and it is probably undergoing strong
tidal dissipation. If such eccentricity is confirmed, it would make it
one of the most eccentric sub-Neptunes known to date. TOI-521 b and
TOI-912 b have very similar densities (4g/cm3), and they lie in the
degenerate region of the mass-radius diagram where different
compositions are plausible, including a volatile-rich composition, or
a rocky core surrounded by a H-He envelope. When compared to the other
THIRSTEE M-dwarf targets, our sample supports the division of
sub-Neptunes into two distinct populations divided by a density gap.
Both planets are interesting targets for atmospheric follow-up in the
context of understanding the temperature-atmospheric feature trend
that starts to emerge thanks to JWST observations.
Description:
ESPRESSO, HARPS, and IRD radial velocity and activity indicators of
TOI-521 and TOI-912.
Objects:
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RA (2000) DE Designation(s)
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15 17 21.67 -80 28 22.5 TOI-912 = TIC 406941612
08 13 22.52 +12 13 18.3 TOI-521 = TIC 27649847
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
toi912e.dat 130 33 ESPRESSO RVs and activity indicators of TOI-912
toi912h.dat 52 22 HARPS RVs and activity indicators of TOI-912
toi521e.dat 71 21 ESPRESSO RVs and activity indicators of TOI-521
toi521i.dat 78 62 IRD RVs and activity indicators of TOI-521
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Byte-by-byte Description of file: toi912e.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Barycentric Julian Date (TDB)
16- 20 F5.2 m/s RV Radial velocity
22- 25 F4.2 m/s e_RV Radial velocity uncertainty
27- 31 F5.2 m2/s2 dLW Differential line width
33- 36 F4.2 m2/s2 e_dLW Differential line width uncertainty
38- 42 F5.2 m/s CRX Chromatic index
44- 47 F4.2 m/s e_CRX Chromatic index uncertainty
49- 54 F6.4 --- NaI Sodium line index (doublet I)
56- 61 F6.4 --- e_NaI Sodium line index (doublet I) uncertainty
63- 68 F6.4 --- NaII Sodium line index (doublet II)
70- 75 F6.4 --- e_NaII Sodium line index (doublet II) uncertainty
77- 82 F6.4 --- Halpha H-alpha line index
84- 89 F6.4 --- e_Halpha H-alpha line index uncertainty
91- 96 F6.1 m/s FWHM Full width half maximum
98-100 F3.1 m/s e_FWHM Full width half maximum uncertainty
102-109 E8.2 km/s BIS Bisector span
111-118 F8.6 km/s e_BIS Bisector span uncertainty
120-124 F5.3 --- SMW S-index
126-130 F5.3 --- e_SMW S-index uncertainty
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Byte-by-byte Description of file: toi912h.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Barycentric Julian Date (TDB)
16- 23 F8.2 m/s RV Radial velocity
25- 28 F4.2 m/s e_RV Radial velocity uncertainty
30- 35 F6.4 km/s FWHM Full width half maximum
37- 44 F8.5 --- Contr Contrast of the CCF
46- 52 F7.3 km/s BIS Bisector span
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Byte-by-byte Description of file: toi521e.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Barycentric Julian Date (TDB)
16- 23 F8.2 m/s RV Radial velocity
25- 28 F4.2 m/s e_RV Radial velocity uncertainty
30- 36 F7.2 m/s FWHM Full width half maximum
38- 41 F4.2 m/s e_FWHM Full width half maximum uncertainty
43- 48 F6.3 --- Contr Contrast of the CCF
50- 54 F5.3 --- e_Contr Contrast of the CCF uncertainty
56- 63 F8.5 km/s BIS Bisector span
65- 71 F7.5 km/s e_BIS Bisector span uncertainty
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Byte-by-byte Description of file: toi521i.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Barycentric Julian Date (TDB)
16- 21 F6.2 m/s RV Radial velocity
23- 27 F5.2 m/s e_RV Radial velocity uncertainty
29- 33 F5.3 km/s FWHM Full width half maximum
35- 39 F5.3 km/s e_FWHM Full width half maximum uncertainty
41- 46 F6.3 m/s dV Line asymmetry
48- 52 F5.3 m/s e_dV Line asymmetry uncertainty
54- 59 F6.3 m2/s2 dLW Differential line width
61- 65 F5.3 m2/s2 e_dLW Differential line width uncertainty
67- 72 F6.2 m/s CRX Chromatic index
74- 78 F5.2 m/s e_CRX Chromatic index uncertainty
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Acknowledgements:
Gaia Lacedelli, glacedelli(at)iac.es
(End) Patricia Vannier [CDS] 28-Nov-2025