Thestellar classification of AF Leporis is F8V(n)k:,[4] matching anF-type main-sequence star that is generating energy throughhydrogen fusion at itscore. (The 'n' indicates "nebulous" lines due to spin, while the 'k' means it displays interstellar absorption lines. The ':' suffix is used to note some uncertainty in the classification.) AF Leporis is classified as aRS Canum Venaticorum variable star,[3] which means it has anactive surface with largestar spots that cause the net luminosity to vary as it rotates.
While some studies consider AF Leporis to be a closespectroscopic binary with a separation of0.021 AU,[8] other studies show no evidence of binarity, and it is likely that the supposed binarity is an artifact resulting from the presence ofstarspots.[10][5]
It is about 24 million years old and is spinning rapidly with aprojected rotational velocity of around 50 km/s,[7] giving it a rotation period of less than a day.[10] The star has 9%[9] more mass than the Sun and 1.25[7] times the Sun's radius. The abundance of elements with mass greater than hydrogen – the star'smetallicity – is higher than in the Sun. AF Leporis is radiating 1.84[8] times the luminosity of the Sun from itsphotosphere at aneffective temperature of 6,130 K.[7]
There have been multiple studies of AF Leporis b, which have found somewhat different parameters. Dynamical mass measurements range from2.8 MJ[9] to5.5 MJ.[5] Values for the planet'sorbital inclination range from50°+9° −12°[7] to~98°,[14] the former consistent with the stellar inclination of54°+11° −9° and suggesting an aligned system.[7] Initial studies found a fairlyeccentric orbit for the planet, but the precovery observations show that its orbit is nearly circular.[15]
AF Leporis b has aneffective temperature of about 750 K (477 °C; 890 °F), corresponding to anearly-T spectral type.[16] Spectroscopic evidence suggests that it has ametal-rich atmosphere withsilicate clouds,[9] though further studies are needed to confirm this.[16]
AF Leporis b was observed with JWSTNIRCam. The brightness of F444W is relative faint, indicating significant absorption due tocarbon monoxide (CO). The strong CO absorption is explained with disequilibrium chemistry and high metallicity. The observations also rule out additional giant planets in the outer region. The study did not find any variability of AF Leporis b.[17] A study withVLT/GRAVITY confirmed many of the previous observations. The GRAVITY instrument did add high precisionastrometry, while at the same time providing aK-band spectrum. The new astrometry together with previous observations was able to constrain the orbit to a circular orbit with an inclination that is aligned with the inclination of the rotation axis of the host star. The K-band spectrum shows prominentmethane (CH4) absorption. The spectrum is also consistent with a metal-rich cloudy atmosphere, with[Fe/H] = 0.75±0.25, consistent with the formation viacore accretion. The temperature was constrained to800±50 Kelvin and the mass was re-estimated to3.75MJ.[18] An observation with VLT/ERIS in the K-band detected CO and H2O, but not CH4 or CO2.[19] Observations with VLT/HiRISE in theH-band on the other hand confirmed the detection of CH4.[6]
A 2025 study assessed the feasibility of detectingexomoons byastrometry (i.e., from variations in the motion of a moon's host planet) around several directly imaged exoplanets withVLTI/GRAVITY. For AF Leporis b, it would theoretically be possible to detect a0.14MJ satellite orbiting at 0.39 AU, while a non-detection would rule out the existence of such a satellite.[20]
^abcSamus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)".VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S.1: B/GCVS.Bibcode:2009yCat....102025S.
^Winterhalder, T. O.; Mérand, A.; et al. (September 2025). "Astrometric exomoon detection by means of optical interferometry".Astronomy & Astrophysics.arXiv:2509.15304.
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