1 Pegasi

1 Pegasi (1 Peg) is a triple star^[10] system in the constellation Pegasus, located approximately 156 light years away from the Sun based on parallax.^[1] It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.09.^[2] The system is moving closer to the Earth with a heliocentric radial velocity of −11 km/s.^[4]

1 Pegasi

Location of 1 Pegasi (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Pegasus
Right ascension	21h 22m 05.19950s [1]
Declination	19° 48′ 16.2375″ [1]
Apparent magnitude (V)	4.09[2]
Characteristics
Spectral type	K1III[3]
U−B color index	+1.05[2]
B−V color index	+1.11[2]
Astrometry
Radial velocity (Rv)	−10.80[4] km/s
Proper motion (μ)	RA: +105.391 mas/yr[1] Dec.: +62.841 mas/yr[1]
Parallax (π)	20.8482±0.1452 mas[1]
Distance	156 ± 1 ly (48.0 ± 0.3 pc)
Absolute magnitude (MV)	0.68[5]
Details[6]
1 Peg A
Mass	1.60±0.18 M☉
Radius	11.89±0.15 R☉
Luminosity	63.5±0.3 L☉
Surface gravity (log g)	2.59[7] cgs
Temperature	4,725±64 K
Metallicity [Fe/H]	+0.01[7] dex
Rotational velocity (v sin i)	1.2[8] km/s
Age	2.04±0.54 Gyr
Other designations
1 Peg, BD+19°4691, FK5 804, GC 29914, HD 203504, HIP 105502, HR 8173, SAO 107073, CCDM J21221+1949A, WDS J21221+1948A[9]
Database references
SIMBAD	data

The primary component is a giant with a stellar classification of K1III,^[3] a star that has exhausted the hydrogen supply at its core and evolved away from the main sequence. Estimated to be two billion years old, 1 Pegasi has 1.6 times the mass of the Sun and has expanded to twelve times the Sun's radius. The star is radiating 64 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,725 K.^[6]

There are several companions in addition to the primary. The brightest, component B, is a magnitude 9.3, K-type main-sequence star with a class of K0 V orbiting at an angular separation of 36.6" from the primary; it is itself a single-lined spectroscopic binary with an orbital period of 3.042 ± 0.011 years and eccentricity of 0.290±0.022.^[11] Visual companions C, with magnitude 12.9 and separation 64.7", and D, with magnitude 9.6 and separation 5.3", have been reported.^[12]