HD 170657

HD 170657 is a star in the southern constellation Sagittarius. It is a suspected variable star that has been measured ranging in apparent visual magnitude from 6.82 down to 6.88,^[5] which is dim enough to be a challenge to view with the naked eye even under ideal conditions. The star is located at a distance of 43 light years from the Sun based on parallax. It is drifting closer with a radial velocity of −43 km/s, and is predicted to come as close as 14.0 light-years in around 266,200 years.^[6] The space velocity components of this star are (U, V, W) = (–41, –26, +6) km/s.^[10]

HD 170657

Observation data Epoch J2000      Equinox J2000
Constellation	Sagittarius
Right ascension	18h 31m 18.96122s[1]
Declination	–18° 54′ 31.7326″[1]
Apparent magnitude (V)	6.81[2]
Characteristics
Evolutionary stage	Main sequence
Spectral type	K2V[3]
U−B color index	+0.56[4]
B−V color index	+0.861±0.007[2]
Variable type	Suspected[5]
Astrometry
Radial velocity (Rv)	−43.16±0.14[6] km/s
Proper motion (μ)	RA: –138.402[1] mas/yr Dec.: –195.274[1] mas/yr
Parallax (π)	75.9773±0.0458 mas[1]
Distance	42.93 ± 0.03 ly (13.162 ± 0.008 pc)
Absolute magnitude (MV)	6.20[2]
Details
Mass	0.79±0.11[7] M☉
Radius	0.75+0.01 −0.04[1] R☉
Luminosity	0.336±0.001[1] L☉
Surface gravity (log g)	4.59[8] cgs
Temperature	5,133±37[8] K
Metallicity [Fe/H]	–0.15[7] dex
Rotational velocity (v sin i)	4.2[8] km/s
Age	7.95[8] Gyr
Other designations
NSV 10944, GJ 716, HD 170657, HIP 90790, SAO 161557, WDS J18313-1855A, LTT 7358[9]
Database references
SIMBAD	data
ARICNS	data

This is a K-type main-sequence star with a stellar classification of K2V,^[3] which indicates that, much like the Sun, it is generating energy at its core using hydrogen fusion. The star has 79%^[7] of the mass of the Sun and 75%^[1] of the Sun's radius. It is nearly eight^[8] billion years old and is spinning with a projected rotational velocity of 4.2 ^[8] The star is radiating 33.6%^[1] of the luminosity of the Sun from its photosphere at an effective temperature of 5,133 K.^[8] When observed with the Spitzer Space Telescope, this star did not display an excess emission of infrared radiation, which may otherwise indicate the presence of an orbiting debris disk.^[11]