Upsilon Pegasi
Aging giant star in the constellation Pegasus
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Upsilon Pegasi, Latinised from υ Pegasi, is a star within the great square[10] in the northern constellation of Pegasus. It has the proper name Alkarab /ˈælkəræb/.[11] This object has a yellow-white hue and is faintly visible to the naked eye with an apparent magnitude of 4.40.[2] It is located at a distance of approximately 170 light-years from the Sun based on parallax,[1] but is drifting closer with a radial velocity of −8.6 km/s.[5] The star is moving through the galaxy at a speed of 50.6 km/s relative to the Sun. Its projected galactic orbit carries it between 18,600 and 26,300 light-years from the center of the galaxy.[6]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Pegasus |
| Right ascension | 23h 25m 22.78350s[1] |
| Declination | +23° 24′ 14.7606″[1] |
| Apparent magnitude (V) | 4.40[2] |
| Characteristics | |
| Evolutionary stage | subgiant[3] |
| Spectral type | F8III[4] |
| U−B color index | +0.14[2] |
| B−V color index | +0.61[2] |
| Astrometry | |
| Radial velocity (Rv) | −8.59[5] km/s |
| Proper motion (μ) | RA: +192.19[1] mas/yr Dec.: +36.12[1] mas/yr |
| Parallax (π) | 19.14±0.18 mas[1] |
| Distance | 170 ± 2 ly (52.2 ± 0.5 pc) |
| Absolute magnitude (MV) | 0.83[6] |
| Details | |
| Mass | 2.17[7] M☉ |
| Radius | 5.97+0.36 −0.19[8] R☉ |
| Luminosity | 43.2±0.8[8] L☉ |
| Surface gravity (log g) | 3.22[7] cgs |
| Temperature | 6,061+97 −176[8] K |
| Metallicity [Fe/H] | −0.01[6] dex |
| Rotational velocity (v sin i) | 73.4[3] km/s |
| Other designations | |
| Alkarab, υ Peg, 68 Pegasi, BD+22°4833, FK5 881, GC 32585, HD 220657, HIP 115623, HR 8905, SAO 91253[9] | |
| Database references | |
| SIMBAD | data |
This object is an aging giant star with a stellar classification of F8III.[4] It is currently in the Hertzsprung gap and is a source of X-ray emission.[3] The star has 2.2[7] times the mass of the Sun and is spinning with a projected rotational velocity of 73.4 km/s.[3] It has an iron abundance of −0.01 dex, or 97.7% of the Sun's. Upsilon Pegasi has six times the girth of the Sun and is radiating 43 times the Sun's luminosity at an effective temperature of 6,061 K.[8]
Nomenclature
υ Pegasi is the star's Bayer designation. The star bore the traditional Arabic name Al Karab ("the Bucket-rope").[12] In 2016, the IAU organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN approved the name Alkarab for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[11]