Eta Pegasi
 Location of η Pegasi (circled) near the center |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Pegasus |
| Right ascension | 22h 43m 00.13743s[1] |
| Declination | +30° 13′ 16.4822″[1] |
| Apparent magnitude (V) | +2.95[2] |
| Characteristics | |
| Spectral type | G2 II + F0 V[3] |
| U−B color index | +0.57[2] |
| B−V color index | +0.86[2] |
| Astrometry | |
| Radial velocity (Rv) | +4.3[4] km/s |
| Proper motion (μ) | RA: –100.06[1] mas/yr Dec.: +15.46[1] mas/yr |
| Parallax (π) | 19.51 ± 0.18[1] mas |
| Distance | 167 ± 2 ly (51.3 ± 0.5 pc) |
| Absolute magnitude (MV) | –1.18[5] |
| Orbit[6] | |
| Period (P) | 813 days |
| Eccentricity (e) | 0.183 |
| Periastron epoch (T) | 2452025 HJD |
| Argument of periastron (ω) (secondary) |
344.7° |
| Semi-amplitude (K1) (primary) |
14.37 km/s |
| Details | |
| η Peg A | |
| Mass | 3.82 ± 0.52[7] M☉ |
| Radius | 18[8] R☉ |
| Luminosity | 247[7] L☉ |
| Surface gravity (log g) | 2.40[9] cgs |
| Temperature | 5,450[7] K |
| Metallicity [Fe/H] | +0.39[9] dex |
| Rotation | 818[5] |
| Rotational velocity (v sin i) | 1.4[6] km/s |
| Other designations | |
Eta Pegasi (η Peg) is a binary star in the constellation Pegasus. It has the traditional name Matar, which comes from the Arabic Al Saʽd al Maṭar (سعد المطر) meaning lucky star of rain.[11] The apparent visual magnitude of this star is +2.95,[2] making this the fifth brightest member of Pegasus. Based upon parallax measurements, the distance to this star is about 167 light-years (51 parsecs).[1]
This system consists of a pair of stars in a binary orbit with a period of 813 days and an eccentricity of 0.183.[6] The primary component is a bright giant star with a stellar classification of G2 II[3] and about four times the mass of the Sun.[5] The interferometry-measured angular diameter of this star, after correcting for limb darkening, is 3.26 ± 0.07 mas,[12] which, at its estimated distance, equates to a physical radius of nearly 18 times the radius of the Sun.[8] It is radiating 247[7] times the luminosity of the Sun from its expanded outer envelope at an effective temperature of 5,450 K.[7] The rotation rate of the star slowed as it expanded, so it has a projected rotational velocity of 1.7 km s−1 with an estimated rotation period of 818 days.[5]
The secondary component is an F-type main sequence star with a classification of F0 V.[3] There are also 2 class G stars further away that may or may not be physically related to the main pair.
Namesakes
USS Matar (AK-119) was a United States Navy Crater class cargo ship named after the star.
References
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