Lambda Serpentis

Lambda Serpentis, Latinized from λ Serpentis, is a star in the constellation Serpens, in its head (Serpens Caput). It has an apparent visual magnitude of 4.43,^[2] making it visible to the naked eye. Based upon parallax measurements, this star lies at a distance of about 38.9 light-years (11.9 parsecs) from Earth.^[1] Lambda Serpentis is moving toward the Solar System with a radial velocity of 66.4 km s⁻¹.^[4] In about 166,000 years, this system will make its closest approach of the Sun at a distance of 7.371 ± 0.258 light-years (2.260 ± 0.079 parsecs), before moving away thereafter.^[9]

Lambda Serpentis

Location of λ Serpentis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Serpens
Right ascension	15h 46m 26.61423s[1]
Declination	+07° 21′ 11.0475″[1]
Apparent magnitude (V)	4.43[2]
Characteristics
Spectral type	G0 V[3]
U−B color index	+0.11[2]
B−V color index	+0.60[2]
Variable type	Suspected
Astrometry
Radial velocity (Rv)	−66.4[4] km/s
Proper motion (μ)	RA: −224.0±0.2 mas/yr[1] Dec.: −69.8±0.3 mas/yr[1]
Parallax (π)	83.92±0.15 mas[1]
Distance	38.87 ± 0.07 ly (11.92 ± 0.02 pc)
Absolute magnitude (MV)	4.01[5]
Details[6]
Mass	1.09±0.04 M☉
Radius	1.363±0.031 R☉
Luminosity	1.98±0.023 L☉
Surface gravity (log g)	4.09[7] cgs
Temperature	5,901±78 K
Metallicity [Fe/H]	−0.03[7] dex
Rotation	24.3+3.7 −4.9 days
Rotational velocity (v sin i)	3[8] km/s
Age	5.4±0.7 Gyr
Other designations
λ Ser, 27 Serpentis, NSV 7246, BD+07°3023, GJ 598, HD 141004, HIP 77257, HR 5868, SAO 121186, 2MASS J15462661+0721109[3]
Database references
SIMBAD	data
Exoplanet Archive	data

This star is 36% larger and 9% more massive than the Sun, although it has a similar stellar classification. It is shining with nearly double the Sun's luminosity and this energy is being radiated from the star's outer atmosphere at an effective temperature of 5,901 K.^[6] A periodicity of 1837 days (5.03 years) was suspected by Morbey & Griffith (1987),^[10] but it is probably bound to stellar activity. However, McDonald Observatory team has set limits to the presence of one or more exoplanets^[10] around Lambda Serpentis with masses between 0.16 and 2 Jupiter masses and average separations spanning between 0.05 and 5.2 Astronomical Units.

Planetary system

In 2020, a candidate planet was detected orbiting Lambda Serpentis (HD 141004). With a minimum mass of 0.043 M_J (13.6 M_🜨) and an orbital period of 15 days, this would most likely be a hot Neptune.^[11] The planet was confirmed in 2021.^[12]

The Lambda Serpentis planetary system^[12]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	≥0.0428+0.0047 −0.0045 MJ	0.1238±0.002	15.5083+0.0016 −0.0018	0.16+0.11 −0.10	—	—