G Herculis

g Herculis is a binary star^[12] system in the northern constellation of Hercules, which makes part of a wide triple star system. It has the Flamsteed designation 30 Herculis, while g Herculis is the Bayer designation. This system is visible to the naked eye as a faint, red-hued point of light. Based upon a measured parallax of 9.2 mas, it is located around 354 light years away from the Sun. The system is moving further from the Earth with a heliocentric radial velocity of 1.5 km/s.^[6]

G Herculis

A light curve for g Herculis, plotted from Hipparcos data[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Hercules
Right ascension	16h 28m 38.54859s[2]
Declination	+41° 52′ 54.0406″[2]
Apparent magnitude (V)	4.3 - 6.3[3]
Characteristics
Evolutionary stage	AGB[4]
Spectral type	M6− III[5]
B−V color index	1.289±0.024[6]
Variable type	SRb[3]
Astrometry
Radial velocity (Rv)	1.49±0.38[6] km/s
Proper motion (μ)	RA: +30.16[2] mas/yr Dec.: −5.14[2] mas/yr
Parallax (π)	9.21±0.18 mas[2]
Distance	354 ± 7 ly (109 ± 2 pc)
Absolute magnitude (MV)	−0.41[7]
Orbit[4]
Period (P)	843.7±21.1 d
Eccentricity (e)	0.37±0.11
Periastron epoch (T)	2,451,918.2±43.9 HJD
Argument of periastron (ω) (secondary)	246±21°
Semi-amplitude (K1) (primary)	2.3±0.3 km/s
Details
g Her A
Mass	1.65±0.30[8] M☉
Radius	230[9] R☉
Luminosity	5,395[9] L☉
Surface gravity (log g)	0.20[10] cgs
Temperature	3,263±23[9] K
Metallicity [Fe/H]	−0.01[10] dex
Other designations
g Her, 30 Her, BD+42°2714, FK5 3303, HD 148783, HIP 80704, HR 6146, SAO 46108[11]
Database references
SIMBAD	data

Characteristics

This is a single-lined spectroscopic binary with an orbital period of 2.310 years and an eccentricity of 0.37.^[4] The visible component is an aging red giant on the asymptotic giant branch^[4] with a stellar classification of M6− III.^[5] According to Samus et al. (2017), it is a semiregular variable of subtype SRb, which ranges between visual magnitudes 4.3 and 6.3 over 89.2 days.^[3][13] It displays cyclical periods of 62.3, 89.5, and 888.9 days.^[4] The star is surrounded by a circumstellar dust shell that seems primarily composed of oxides of iron, magnesium, and aluminium, rather than silicates.^[14]

In addition to the spectroscopic pair, there is a much wider star sharing similar proper motion and distance. It is a so-called proper motion companion. This star has a projected separation of 1,060 astronomical units from the inner pair. Its mass is estimated at 0.4 solar masses, and its apparent magnitude is much fainter than that of g Herculis.^[15]