The GAPS programme at TNG - LXXI. A sub-Neptune suitable for atmospheric characterization in a multiplanet and mutually inclined system orbiting the bright K dwarf TOI-5789 (HIP 99452)

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Volume 707 (March 2026)

A&A, 707 (2026) A197

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Table 2

TOI-5789 system parameters.

Host star parameters	Value and 1σ error
Systemic velocity γ [ms⁻¹]	−49 315.60 ± 0.11
RV jitter σ_RV,jit [ m s⁻¹ ]	1.12 ± 0.09
Phot. jitter σ_phot,s54	7.11 ± 1.28 E-05
Phot. jitter σ_phot,s81	1.50 ± 0.18 E-04
Limb-darkening coefficient q₁	${0.40}_{- 0.16}^{+ 0.18}$ $Mathematical equation: $0.40_{ - 0.16}^{ + 0.18}$$
Limb-darkening coefficient q₂	0.51 ± 0.35
Limb-darkening coefficient u₁	${0.61}_{- 0.41}^{+ 0.44}$ $Mathematical equation: $0.61_{ - 0.41}^{ + 0.44}$$
Limb-darkening coefficient u₂	−0.01 ± 0.42

Planetary parameters

TOI-5789 b	Value and 1σ error

Inferior conjunction time T_c[BJDT_DB − 2 450 000]	10 358.054 (62)
Orbital period P [days]	2.76369 (96)
Orbital semimajor axis a [au]	0.03608 ± 0.00045
Orbital eccentricity e	0 (fixed)
RV semiamplitude K [ m s⁻¹]	1.10 ± 0.14
Planet minimum mass M_p sin i [M_⊕]	2.12 ± 0.28
Equilibrium temperature⁽¹⁾ T_eq [K]	1201 ± 26

TOI-5789 c

Transit Time T_c[BJD_TDB − 2 450 000]	10 151.15868 (49)
Orbital period P [days]	12.927748 (16)
Transit duration T₁₄ [h]	2.019 ± 0.050
Radius ratio R_p/R_✶	${0.0314}_{- 0.0013}^{+ 0.0018}$ $Mathematical equation: $0.0314_{ - 0.0013}^{ + 0.0018}$$
Inclination i [deg]	88.02 ±^- 0.13
Impact parameter b	0.903 ± 0.015
Orbital semimajor axis a [au]	0.1009 ± 0.0013
Orbital eccentricity e	<0.067
RV semiamplitude K [m s⁻¹]	1.56 ± 0.15
Planet radius R_p [R_⊕]	${2.86}_{- 0.15}^{+ 0.18}$ $Mathematical equation: $2.86_{ - 0.15}^{ + 0.18}$$
Planet mass M_p [M_⊕]	5.00 ± 0.50
Planet density ρ_p [g cm⁻³]	1.16 ± 0.23
Planet surface gravity log g_p [cgs]	2.77 ± 0.06
Equilibrium temperature⁽¹⁾ T_eq [K]	718±15

TOI-5789 d

Inferior conjunction time T_c[BJD_TDB − 2 450 000]	10 347.48 ± 0.99
Orbital period P [days]	29.65 ± 0.12
Orbital semimajor axis a [au]	0.1756 ± 0.0023
Orbital eccentricity e	<0.096
RV semiamplitude K [m s⁻¹]	1.01 ± 0.16
Planet minimum mass M_p sin i [M_⊕]	4.29 ± 0.68
Equilibrium temperature⁽¹⁾ T_eq [K]	545 ±10

TOI-5789 e

Inferior conjunction time T_c[BJD_TDB − 2 450 000]	10 359.05 ± 1.17
Orbital period P [days]	62.98 ± 0.22
Orbital semimajor axis a [au]	0.2901 ± 0.0037
Orbital eccentricity e	<0.071
RV semiamplitude K [m s⁻¹]	2.13 ± 0.17
Planet minimum mass M_p sin i [M_⊕]	11.61 ± 0.97
Equilibrium temperature⁽¹⁾ T_eq [K]	424 ±8

Notes. – ¹Blackbody equilibrium temperature assuming a null Bond albedo and uniform heat redistribution to the night side.

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