HD 165634
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  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 08m 04.97982s[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]
