HD 165634

HD 165634

Location of HD 165634 (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Sagittarius
Right ascension	18^h 08^m 04.97982^s[1]
Declination	−28° 27′ 25.5316″[1]
Apparent magnitude (V)	4.56[2]
Characteristics
Spectral type	G7:IIIb CN−1 CH−3.5 HK+1[3]
U−B color index	+0.75[2]
B−V color index	+0.95[2]
Astrometry
Radial velocity (Rv)	−4.87[4] km/s
Proper motion (μ)	RA: +25.43[1] mas/yr Dec.: −31.18[1] mas/yr
Parallax (π)	9.62 ± 0.26 mas[1]
Distance	339 ± 9 ly (104 ± 3 pc)
Absolute magnitude (MV)	−0.53[5]
Details[6]
Mass	3.38 M☉
Radius	16.98 R☉
Luminosity	168 L☉
Surface gravity (log g)	2.51 cgs
Temperature	5,043 K
Metallicity [Fe/H]	−0.05 dex
Rotational velocity (v sin i)	2.6[7] km/s
Other designations
CD−28°14174, FK5 3439, GC 24694, HD 165634, HIP 88839, HR 6766, SAO 186328, GSC 06854-04372[8]
Database references
SIMBAD	data

HD 165634 is a star in the southern constellation of Sagittarius. It has a yellow hue and is faintly visible to the naked eye with apparent visual magnitude of 4.56.[2] The star is located at a distance of approximately 339 light years from the Sun based on parallax,[1] but is drifting closer with a radial velocity of −5 km/s.[4] It has an absolute magnitude of −0.53.[5]

This is a CH-peculiar[9] giant star with a stellar classification of G7:IIIbCN-1CH-3.5HK+1, and has been designated as a standard example of this spectral type.[3] This notation indicates a G-type giant (G7:IIIb) with underabundances of CN and CH molecules. It is a rare "weak G–band star", showing an abnormally weak G band of the molecule CN. This indicates an underabundance of carbon in the stellar atmosphere; the abundances of most other elements are otherwise normal for a star at its evolutionary stage.[10] The depletion of carbon is a reflection of internal processes while the star is on the red giant branch, accompanied by deep mixing.[11]

In 2000, Böhm-Vitense and collaborators suggested that the star has an evolved white dwarf companion. This object can explain an excess flux of ultraviolet radiation, and a mass-transfer could be the source for a mild nitrogen excess on the visible component. The progenitor star was not very evolved because there is no excess of s-process elements such as barium. It may even have been a low-mass star that lost its envelope.[9]

References

1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Vizier catalog entry
2. Ducati, J. R. (2002). "Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
3. Keenan, Philip C.; McNeil, Raymond C. (1989). "The Perkins catalog of revised MK types for the cooler stars". The Astrophysical Journal Supplement Series. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
4. Nidever, David L.; et al. (2002). "Radial Velocities for 889 Late-Type Stars". The Astrophysical Journal Supplement Series. 141 (2): 503–522. arXiv:astro-ph/0112477. Bibcode:2002ApJS..141..503N. doi:10.1086/340570. S2CID 51814894.
5. 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. Vizier catalog entry
6. Reffert, Sabine; et al. (2015). "Precise radial velocities of giant stars". Astronomy & Astrophysics. 574: A116. arXiv:1412.4634. Bibcode:2015A&A...574A.116R. doi:10.1051/0004-6361/201322360. hdl:10722/215277. S2CID 59334290. Vizier catalog entry
7. De Medeiros, J. R.; Alves, S.; Udry, S.; Andersen, J.; Nordström, B.; Mayor, M. (2014). "A catalog of rotational and radial velocities for evolved stars". Astronomy & Astrophysics. 561: A126. arXiv:1312.3474. Bibcode:2014A&A...561A.126D. doi:10.1051/0004-6361/201220762. S2CID 54046583. Vizier catalog entry
8. "HD 165634". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-11-29.
9. Böhm-Vitense, Erika; et al. (April 2000). "Do All BA II Stars Have White Dwarf Companions?". The Astrophysical Journal. 533 (2): 969–983. Bibcode:2000ApJ...533..969B. doi:10.1086/308678.
10. Sneden, C.; et al. (June 1978). "Light-element abundances in the weak G-band star HR 6766". Astrophysical Journal. 222: 585–594. Bibcode:1978ApJ...222..585S. doi:10.1086/156173.
11. Palacios, A.; et al. (February 2012). "Weak G-band stars on the H-R diagram: clues to the origin of the Li anomaly". Astronomy & Astrophysics. 538: 11. arXiv:1112.2973. Bibcode:2012A&A...538A..68P. doi:10.1051/0004-6361/201117988. S2CID 119186052. A68.