Gliese 758

Gliese 758 is a star in the northern constellation of Lyra. At about magnitude 6 it is a challenge to view with the naked eye even in good seeing conditions, but can be easily seen through a small telescope or binoculars. Parallax measurements from the Hipparcos mission give it an estimated distance of around 50.9 light-years (15.6 parsecs) from Earth.

Gliese 758

Discovery image of Gliese 758 B, taken with Subaru HiCIAO in the near infrared
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Lyra
Right ascension	19h 23m 34.013166s[1]
Declination	+33° 13′ 19.078368″[1]
Apparent magnitude (V)	6.36[2]
Characteristics
Spectral type	G8V[3]+T7[4]
U−B color index	+0.455[2]
B−V color index	+0.799[2]
Astrometry
Radial velocity (Rv)	−21.62±0.12[1] km/s
Proper motion (μ)	RA: 81.966±0.013 mas/yr[1] Dec.: 160.158±0.016 mas/yr[1]
Parallax (π)	64.0703±0.0154 mas[1]
Distance	50.91 ± 0.01 ly (15.608 ± 0.004 pc)
Absolute magnitude (MV)	5.37[5]
Orbit[6]
Primary	Gliese 758 A
Companion	Gliese 758 B
Period (P)	131.276+15.078 −12.080 yr
Semi-major axis (a)	25.409+1.944 −1.626 AU
Eccentricity (e)	0.365+0.079 −0.082
Inclination (i)	38.080+5.438 −4.808°
Longitude of the node (Ω)	349.680+5.776 −6.263°
Periastron epoch (T)	2,421,289.845+3,708.120 −4,680.545
Argument of periastron (ω) (secondary)	175.102+11.951 −14.709°
Semi-amplitude (K1) (primary)	0.139318+0.009603 −0.008036 km/s
Details
Gliese 758 A
Mass	0.93±0.03[6] M☉
Radius	0.88[7] R☉
Surface gravity (log g)	4.55[7] cgs
Temperature	5305[1] K
Metallicity [Fe/H]	0.18[3] dex
Age	7.7–8.7[8] Gyr
Gliese 758 B
Mass	36.387+1.210 −1.081[6] MJup
Surface gravity (log g)	4.3 ±0.5[4] cgs
Temperature	741 ±25[4] K
Other designations
GJ 758, BD+32 3411, HD 182488, HIP 95319, HR 7368, PPM 82821, SAO 68239[9]
Database references
SIMBAD	A
	B

Properties

This is a Sun-like star with 97% of the Sun's mass and 88% of the radius of the Sun. The spectrum matches a stellar classification of G8V,^[3] identifying it as a G-type main-sequence star that is generating energy through the nuclear fusion of hydrogen at its core. It is radiating this energy into space from its outer envelope at an effective temperature of 5,425 K.^[3] Estimates of its age put it at about 7.7–8.7 billion years old,^[8] although some measurements give it an age as low as 720 million years.^[7] The abundance of elements other than hydrogen and helium, what astronomers term the star's metallicity, are 51% higher than in the Sun.^[3]

Companion

In November 2009, a team using the HiCIAO instrument of the Subaru Telescope imaged a substellar companion orbiting the star. This brown dwarf, designated Gliese 758 B, was estimated to be of approximately 10 to 40 Jupiter masses. A second candidate object was also detected, which was given the designation Gliese 758 C.^[10][11][12] Follow-up studies of the system refined the mass range of Gliese 758 B, indicating it to be a companion with approximately 30 to 40 Jupiter masses, and revealed that Gliese 758 C is a background star which is not physically associated with the Gliese 758 system.^[13] On the other hand, a younger age was suggested from the kinematic stellar grouping.

The most recent parameters for Gliese 758 B as of 2022 come from a combination of data from radial velocity, astrometry, and imaging,^[14][15][6] showing that it is about 36 times the mass of Jupiter, and on an eccentric orbit with a semi-major axis of about 25.4 astronomical units and an orbital period of about 131 years.^[6]

First near-infrared spectroscopy was published in 2017. This team used the Hale Telescope at Palomar Observatory to obtain a low-resolution spectrum. Comparison with archived IRTF/SpeX spectra of brown dwarfs resulted in a best fit to a spectral type of T7.0 ±1.0. The modelling of the spectrum indicates a temperature of 741 ± 25 K, which is slightly hotter than previously thought. A later spectral type and lower temperature is not excluded.^[4]

See also

• Direct imaging of extrasolar planets
• Lists of exoplanets