Xi Herculis

Xi Herculis is a solitary^[11] star located within the northern constellation of Hercules. The star is visible to the naked eye with an apparent visual magnitude of 3.70.^[2] Based upon an annual parallax shift of 23.85 mas as seen from Earth, it is located 137 light years from the Sun.^[1] At that distance, the visual magnitude of the star is diminished by an extinction factor of 0.05 due to interstellar dust. It is a suspected member of the Sirius stream of co-moving stars.^[12]

A light curve for Xi Herculis, plotted from Hipparcos data^[13]

Xi Herculis

ξ Herculis in optical light
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Hercules
Right ascension	17h 57m 45.88567s[1]
Declination	+29° 14′ 52.3660″[1]
Apparent magnitude (V)	3.70[2]
Characteristics
Evolutionary stage	red clump[3]
Spectral type	G8 III[4]
U−B color index	+0.66[2]
B−V color index	+0.93[2]
Astrometry
Radial velocity (Rv)	−1.65±0.17[5] km/s
Proper motion (μ)	RA: 81.919 mas/yr[1] Dec.: −18.962 mas/yr[1]
Parallax (π)	23.8544±0.1068 mas[1]
Distance	136.7 ± 0.6 ly (41.9 ± 0.2 pc)
Absolute magnitude (MV)	+0.62[6]
Details
Mass	2.01[7] M☉
Radius	9.94±0.09[8] R☉
Luminosity	57.2±2.1[8] L☉
Surface gravity (log g)	2.87±0.09[9] cgs
Temperature	5,032±48[8] K
Metallicity [Fe/H]	+0.09±0.04[9] dex
Rotation	67[3] d
Rotational velocity (v sin i)	2.8[5] km/s
Age	2.48[7] Gyr
Other designations
ξ Her, 92 Her, BD+29°3156, HD 163993, HIP 87933, HR 6703, SAO 85590[10]
Database references
SIMBAD	data

This is an evolved G-type giant star with a stellar classification of G8 III.^[4] It is a red clump star, which means it is on the horizontal branch and generating energy through the thermonuclear fusion of hydrogen at its core. The star is emitting X-rays with a luminosity of 3.03×10³⁰ erg s⁻¹ in the 0.3–10 keV band.^[3] It has twice^[7] the mass of the Sun but, at the age of two and a half billion years,^[7] it has expanded to 10 times the Sun's radius. The star is radiating 57 times the solar luminosity from its photosphere at an effective temperature of 5,032 K.^[8]

Xi Herculis was discovered to be a variable star when the Hipparcos data was analyzed.^[14] It's is a semiregular variable star, oscillating in brightness by 3 hundredths of a magnitude, over a period of 120.8 days.^[15]

Chinese name

In R.H.Allen's book Star Names: Their Lore and Meaning, this star, together with ν Her and 99 Her (b Herculis) represent the state of Zhongshan (or Chung Shan' "the Middle Mountain"),^[16] but in Chinese literature, that names is applied to ο Her.^[17]

Markov 1, the mini teapot

One third of a degree to the north-northwest of Xi Herculis is the location of a telescopic asterism in the shape of a teapot. This teapot (Markov 1) could be seen as a somewhat twisted small equivalent of the large and easy to recognize teapot asterism in the constellation Sagittarius.