The GAPS Programme at TNG - LXXIII. Confirmation of the hot sub-Neptune TOI-4602 b (HD 25295 b), a key target for future atmospheric characterization

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Volume 709 (May 2026)

A&A, 709 (2026) A270

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Table B.1

TOI-4602 parameters from the transit and RV joint fit, obtained with one planet on a circular orbit model (M1 model).

Parameter	Prior^(a)	Value (circular model)	Value (eccentric model)
Model parameters
Orbital period P_orb (days)	𝒩[3.98,0.2]	${3.9812999}_{- 0.0000048}^{+ 0.0000047}$ $Mathematical equation: $3.9812999_{ - 0.0000048}^{ + 0.0000047}$$	${3.9812997}_{- 0.0000046}^{+ 0.0000048}$ $Mathematical equation: $3.9812997_{ - 0.0000046}^{ + 0.0000048}$$
Central time of the first transit T₀ (BJD - 2 450 000)	𝒰[10590, 10595]	${10591.50097}_{- 0.00073}^{+ 0.00066}$ $Mathematical equation: $10591.50097_{ - 0.00073}^{ + 0.00066}$$	${10591.50080}_{- 0.00076}^{+ 0.00070}$ $Mathematical equation: $10591.50080_{ - 0.00076}^{ + 0.00070}$$
Scaled planetary radius R_p/R_⋆	𝒰[0, 0.5]	0.02083 ± 0.00026	0.02089 ± 0.00076
Impact parameter, b	𝒰[0, 2]	${0.17}_{- 0.12}^{+ 0.16}$ $Mathematical equation: $0.17_{ - 0.12}^{ + 0.16}$$	${0.22}_{- 0.15}^{+ 0.20}$ $Mathematical equation: $0.22_{ - 0.15}^{ + 0.20}$$
Radial velocity semi-amplitude variation K (m s⁻¹)	𝒰[0.01,30]	2.39±0.40	2.76± 0.38

Derived parameters
Planetary radius (R_J)		${0.219}_{- 0.020}^{+ 0.021}$ $Mathematical equation: $0.219_{ - 0.020}^{ + 0.021}$$	0.220±0.020
Planetary radius (R_⊕)		2.45 ±0.23	2.46±0.23
Planetary mass (M_J)		${0.0174}_{- 0.0030}^{+ 0.0029}$ $Mathematical equation: $0.0174_{ - 0.0030}^{ + 0.0029}$$	0.0195±0.027
Planetary mass (M_⊕)		${5.53}_{- 0.94}^{+ 0.93}$ $Mathematical equation: $5.53_{ - 0.94}^{ + 0.93}$$	${6.19}_{- 0.85}^{+ 0.86}$ $Mathematical equation: $6.19_{ - 0.85}^{ + 0.86}$$
Eccentricity e		0 (fixed)	0.228±0.057
Scaled semi-major axis a/R_⋆		${8.90}_{- 0.35}^{+ 0.13}$ $Mathematical equation: $8.90_{ - 0.35}^{ + 0.13}$$	${9.22}_{- 0.65}^{+ 0.63}$ $Mathematical equation: $9.22_{ - 0.65}^{ + 0.63}$$
Semi-major axis a (AU)		${0.04747}_{- 0.00036}^{+ 0.00035}$ $Mathematical equation: $0.04747_{ - 0.00036}^{ + 0.00035}$$	0.04746±0.00035
Argument of periastron ω_P (deg)		90 (fixed)	$- 157_{- 21}^{+ 16}$ $Mathematical equation: $ - 157_{ - 21}^{ + 16}$$
Orbital inclination i (deg)		${88.93}_{- 1.1}^{+ 0.74}$ $Mathematical equation: $88.93_{ - 1.1}^{ + 0.74}$$	${88.67}_{- 1.2}^{+ 0.89}$ $Mathematical equation: $88.67_{ - 1.2}^{ + 0.89}$$
Transit duration T₄₁ (days)		0.14364±0.00098	${0.135}_{- 0.010}^{+ 0.011}$ $Mathematical equation: $0.135_{ - 0.010}^{ + 0.011}$$
Transit duration T₃₂ (days)		${0.13744}_{- 0.00096}^{+ 0.00095}$ $Mathematical equation: $0.13744_{ - 0.00096}^{ + 0.00095}$$	0.129±0.010

Calculated parameters
Equilibrium temperature T_eq (K)		1344±80	1321±78
Planetary density ρ_P (g cm⁻³)		2.18±0.77	2.41±0.82
Scale height H (km)		538±140	476±114
δ_λ (ppm)		60±20	53±17
Transmission Spectroscopy Metric (TSM)		140±54	125±46
Insolation (S_⊕)		664±42	620±38

Other system parameters
Jitter term σ_{HARPS −N} (m s⁻¹)	𝒰[0, 20]	${1.58}_{- 0.23}^{+ 0.26}$ $Mathematical equation: $1.58_{ - 0.23}^{ + 0.26}$$	${1.33}_{- 0.21}^{+ 0.25}$ $Mathematical equation: $1.33_{ - 0.21}^{ + 0.25}$$
Offset γ_{HARPS −N} (m s⁻¹)	𝒰[-58514.0504, -38502.3977]	-48508.55±0.26	$- {48508.55}_{- 0.27}^{+ 0.25}$ $Mathematical equation: $ - 48508.55_{ - 0.27}^{ + 0.25}$$
Jitter term $σ_{T E S S_{Sect43}}$ $Mathematical equation: ${\sigma _{TES{S_{{\rm{Sect43}}}}}}$$ (ppm)	𝒰[0, 0.0329]	0.0002613±0.0000036	${0.0002613}_{- 0.0000036}^{+ 0.0000037}$ $Mathematical equation: $0.0002613_{ - 0.0000036}^{ + 0.0000037}$$
Jitter term $σ_{T E S S_{Sect44}}$ $Mathematical equation: ${\sigma _{TES{S_{{\rm{Sect44}}}}}}$$ (ppm)	𝒰[0, 0.0328]	${0.0002923}_{- 0.0000035}^{+ 0.0000036}$ $Mathematical equation: $0.0002923_{ - 0.0000035}^{ + 0.0000036}$$	${0.0002924}_{- 0.0000037}^{+ 0.0000036}$ $Mathematical equation: $0.0002924_{ - 0.0000037}^{ + 0.0000036}$$
Jitter term $σ_{T E S S_{Sect70}}$ $Mathematical equation: ${\sigma _{TES{S_{{\rm{Sect70}}}}}}$$ (ppm)	𝒰[0, 0.0326]	${0.0001863}_{- 0.0000041}^{+ 0.0000042}$ $Mathematical equation: $0.0001863_{ - 0.0000041}^{ + 0.0000042}$$	${0.0001864}_{- 0.0000042}^{+ 0.0000041}$ $Mathematical equation: $0.0001864_{ - 0.0000042}^{ + 0.0000041}$$
Jitter term $σ_{T E S S_{Sect71}}$ $Mathematical equation: ${\sigma _{TES{S_{{\rm{Sect71}}}}}}$$ (ppm)	𝒰[0, 0.0341]	${0.0002044}_{- 0.0000042}^{+ 0.0000041}$ $Mathematical equation: $0.0002044_{ - 0.0000042}^{ + 0.0000041}$$	0.0002043 ± 0.0000042
Jitter term $σ_{T E S S_{Sect86}}$ $Mathematical equation: ${\sigma _{TES{S_{{\rm{Sect86}}}}}}$$ (ppm)	𝒰[0, 0.0374]	${0.0002297}_{- 0.0000045}^{+ 0.0000044}$ $Mathematical equation: $0.0002297_{ - 0.0000045}^{ + 0.0000044}$$	${0.0002297}_{- 0.0000046}^{+ 0.0000045}$ $Mathematical equation: $0.0002297_{ - 0.0000046}^{ + 0.0000045}$$
Stellar density ρ_⋆ (ρ_⊙)	𝒩[0.71, 0.16]	${0.598}_{- 0.067}^{+ 0.026}$ $Mathematical equation: $0.598_{ - 0.067}^{ + 0.026}$$	${0.66}_{- 0.13}^{+ 0.15}$ $Mathematical equation: $0.66_{ - 0.13}^{ + 0.15}$$
Limb darkening c₁	𝒩[0.3876, 0.2]	0.39±0.11	0.39±0.11
Limb darkening c₂	𝒩[0.1413, 0.2]	0.08^±0.16	0.08±0.15

Note. Parameter estimates and corresponding uncertainties are defined as the median and the 16th and 84th percentiles of the posterior distributions. ^(a) [a, b] refers to uniform priors between a and b, 𝒩[a, b] to Gaussian priors with median a and standard deviation b. ^(b) Parameter estimates and corresponding uncertainties are defined as the median and the 16th and 84th percentiles of the posterior distributions.

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