HD 170657

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]
Distance42.93 ± 0.03 ly
(13.162 ± 0.008 pc)
Absolute magnitude (MV)6.20[2]
Details
Mass0.79±0.11[7] M☉
Radius0.75+0.01
−0.04[1] R☉
Luminosity0.336±0.001[1] L☉
Surface gravity (log g)4.59[8] cgs
Temperature5,133±37[8] K
Metallicity [Fe/H]–0.15[7] dex
Rotational velocity (v sin i)4.2[8] km/s
Age7.95[8] Gyr
Other designations
NSV 10944, GJ 716, HD 170657, HIP 90790, SAO 161557, WDS J18313-1855A, LTT 7358[9]
Database references
SIMBADdata
ARICNSdata

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]

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]

  1. ^ a b c d e f g h i Cite error: The named reference GaiaDR2 was invoked but never defined (see the help page).
  2. ^ a b c Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference apj132_1_161 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference mnrassa31_7 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference csvs was invoked but never defined (see the help page).
  6. ^ a b Cite error: The named reference Bailer2018 was invoked but never defined (see the help page).
  7. ^ a b c Cite error: The named reference apj159_1_141 was invoked but never defined (see the help page).
  8. ^ a b c d e f g Cite error: The named reference Earle2017 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference cns was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference apj705_1_89 was invoked but never defined (see the help page).