HD 134606

HD 134606 is a yellow-hued star with a planetary system, positioned in the southern constellation of Apus. It is below the nominal limit for visibility with the naked eye, having an apparent visual magnitude of 6.86.^[2] Based upon an annual parallax shift of 37.3 mas, it is located 87.44 light-years away. The star appears to be moving further from the Earth with a heliocentric radial velocity of +1.9 km/s.^[1]

HD 134606

Observation data Epoch J2000      Equinox J2000
Constellation	Apus
Right ascension	15h 15m 15.04464s[1]
Declination	−70° 31′ 10.6449″[1]
Apparent magnitude (V)	6.86[2]
Characteristics
Evolutionary stage	subgiant[1]
Spectral type	G6 IV[3]
B−V color index	0.740±0.001[2]
Astrometry
Radial velocity (Rv)	+1.94±0.12[1] km/s
Proper motion (μ)	RA: −177.871 mas/yr[1] Dec.: −164.709 mas/yr[1]
Parallax (π)	37.3020±0.0182 mas[1]
Distance	87.44 ± 0.04 ly (26.81 ± 0.01 pc)
Absolute magnitude (MV)	4.74[2]
Details[4]
Mass	1.046+0.070 −0.059 M☉
Radius	1.158+0.039 −0.036 R☉
Luminosity	1.161+0.071 −0.049 L☉
Surface gravity (log g)	4.330+0.044 −0.041 cgs
Temperature	5,576+86 −85 K
Metallicity [Fe/H]	+0.343+0.081 −0.084 dex
Rotation	42.0±3.9 d
Age	7.3+3.6 −3.4 Gyr
Other designations
CD−70°1258, GC 20455, HD 134606, HIP 74653, SAO 257257, LTT 6064, 2MASS J15151504-7031105[5]
Database references
SIMBAD	data
Exoplanet Archive	data

This is an evolving G-type subgiant star with a stellar classification of G6 IV^[3] and is not considered magnetically active, having a chromospheric activity index of −5.04.^[6] It has about the same^[7] mass as the Sun but is 25% more luminous.^[2] The photosphere is radiating energy at an effective temperature of 5,614 K.^[7] It has a higher than solar metallicity – a term astronomers use to describe the abundance of elements other than hydrogen and helium.^[7]

There is a companion star of spectral type M3V at a separation of ~1500 AU, designated L 72-1.^[8][4] This companion presents a bimodal distribution of the Gaia DR3 G-band light-curve, indicating that it is a close binary.^[9]

Planetary system

The discovery of a planetary system orbiting HD 134606 was announced in 2011, following an eight-year survey carried out at the La Silla Observatory in Chile. The detection was made via the radial velocity method using the HARPS instrument. Applying a Keplerian fit to the data suggested the presence of three planets in moderately eccentric orbits.^[10] None of the planetary orbits displays a mean motion resonance with the others.^[11]

The system was updated by a 2024 study, which confirmed the three previously reported planets, though with a longer period for planet d, and detected two new ones. While all five planets are very likely to be real, the study advises caution regarding planet f due to the similarity of its period to the lunar cycle. The five planets range from super-Earth to super-Neptune mass, and the outermost, HD 134606 d, is a small gas giant orbiting within the habitable zone that may be a candidate for future space-based direct imaging missions. A long-period radial velocity trend was also detected, suggesting the presence of a distant sixth substellar companion.^[4]

The HD 134606 planetary system^[4]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
e	≥2.34+0.35 −0.34 M🜨	0.0527+0.0011 −0.0012	4.3203+0.00051 −0.00047	0.2+0.14 −0.13	—	—
b	≥9.09+0.64 −0.63 M🜨	0.1046+0.0023 −0.0024	12.089+0.0016 −0.0015	0.092+0.054 −0.053	—	—
f	≥5.63+0.72 −0.69 M🜨	0.1784+0.0039 −0.0041	26.915±0.016	0.081+0.1 −0.059	—	—
c	≥11.31+1.0 −0.99 M🜨	0.3007+0.0066 −0.0069	58.883+0.041 −0.039	0.055+0.062 −0.04	—	—
d	≥44.8±2.9 M🜨	1.941+0.043 −0.046	966.5+5.3 −6.9	0.092±0.045	—	—