HD 170657

HD 170657

Observation data Epoch J2000      Equinox J2000
Constellation	Sagittarius
Right ascension	18^h 31^m 18.96122^s[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

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]

References

1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
2. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
3. Gray, R. O.; et al. (July 2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637. S2CID 119476992.
4. Corben, P. M.; Carter, B. S.; Banfield, R. M.; Harvey, G. M. (1972). "UBV Photometry of 500 Southern Stars [erratum: 1973MNSSA..32...48C]". Monthly Notes of the Astronomical Society of Southern Africa. 31: 7. Bibcode:1972MNSSA..31....7C.
5. Kukarkin, B. V.; et al. (1981). "Nachrichtenblatt der Vereinigung der Sternfreunde e.V. (Catalogue of suspected variable stars)". Nachrichtenblatt der Vereinigung der Sternfreunde. Moscow: Academy of Sciences USSR Shternberg. Bibcode:1981NVS...C......0K.
6. Bailer-Jones, C.A.L.; et al. (2018). "New stellar encounters discovered in the second Gaia data release". Astronomy & Astrophysics. 616: A37. arXiv:1805.07581. Bibcode:2018A&A...616A..37B. doi:10.1051/0004-6361/201833456. S2CID 56269929.
7. Valenti, Jeff A.; Fischer, Debra A. (July 2005). "Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs". The Astrophysical Journal Supplement Series. 159 (1): 141–166. Bibcode:2005ApJS..159..141V. doi:10.1086/430500.
8. Luck, R. Earle (January 2017). "Abundances in the Local Region II: F, G, and K Dwarfs and Subgiants". The Astronomical Journal. 153 (1): 19. arXiv:1611.02897. Bibcode:2017AJ....153...21L. doi:10.3847/1538-3881/153/1/21. S2CID 119511744. 21.
9. "HD 170657". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-11-09.
10. Gliese, W. (1969). "Catalogue of Nearby Stars". Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg. 22. Heidelberg: Veröffentlichungen des Astronomischen Rechen-Instituts: 1. Bibcode:1969VeARI..22....1G.
11. Lawler, S. M.; et al. (November 2009). "Explorations Beyond the Snow Line: Spitzer/IRS Spectra of Debris Disks Around Solar-type Stars". The Astrophysical Journal. 705 (1): 89–111. arXiv:0909.0058. Bibcode:2009ApJ...705...89L. doi:10.1088/0004-637X/705/1/89. S2CID 1272803.