Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Aquarius |
Right ascension | 20h 39m 24.8927s [1] |
Declination | +00° 29′ 11.155″ [1] |
Apparent magnitude (V) | 5.151 [2] |
Characteristics | |
Evolutionary stage | horizontal branch [3] |
Spectral type | K1III [4] |
U−B color index | 0.936 [2] |
B−V color index | 1.060 [2] |
Astrometry | |
Radial velocity (Rv) | −40.93(3) [5] km/s |
Proper motion (μ) |
RA: 96.805(120)
mas/
yr
[1] Dec.: −10.140(94) mas/ yr [1] |
Parallax (π) | 12.3852 ± 0.1134 mas [1] |
Distance | 263 ± 2
ly (80.7 ± 0.7 pc) |
Absolute magnitude (MV) | 0.77 [6] |
Orbit [5] | |
Primary | 1 Aquarii A |
Companion | 1 Aquarii B |
Period (P) | 1966.7±2.9 days |
Eccentricity (e) | 0.368±0.009 |
Periastron epoch (T) | 54740±7 |
Argument of periastron (ω) (secondary) | 150.7±1.6° |
Semi-amplitude (K1) (primary) | 3.24±0.04 km/s |
Details | |
Mass | 1.50±0.43 [7] M☉ |
Radius | 11 [8] R☉ |
Luminosity | 53.7 [8] L☉ |
Surface gravity (log g) | 2.63±0.11 [7] cgs |
Temperature | 4715±15 [9] K |
Metallicity | −0.12 [6] |
Rotational velocity (v sin i) | 1.8 [6] km/s |
Age | 1.26 [7] Gyr |
Other designations | |
Database references | |
SIMBAD | data |
1 Aquarii is a binary star [5] system in the zodiac constellation of Aquarius, about 263 light years away from the Sun. [1] 1 Aquarii is the Flamsteed designation. It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 5.151, [2] located a degree north of the celestial equator. [5] The system is moving closer to the Earth with a heliocentric radial velocity of −41 km/s. [5]
Systematic observation for determining the orbit of this system began in 2002, some eighty years following the first radial velocity measurements. It is a single-lined spectroscopic binary with an orbital period of 5.385 yr and an eccentricity of 0.368. [5] The visible component is an aging giant star with a stellar classification of K1III. [4] At the age of 1.26 [7] billion years old it is a red clump giant, which indicates it is on the horizontal branch and is generating energy through helium fusion at its core. [3] The star has 1.5 [7] times the mass of the Sun and has expanded to 11 [8] times the Sun's radius. It is radiating 53.7 [8] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,715 K. [9]
The mass of the companion appears small, suggesting a red dwarf no higher than class M5. [5] In addition to the spectroscopic companion there are two faint optical companions that have no physical relation to 1 Aqr. [11]
1 Aquarii was known to the ancients as al-sa'd al-malik, or "the lucky star of the king." Interpreting the unexpressed Arabic vowels, al-sa'd al-mulk, gives an alternate translation of "the lucky star of the kingdom." In English, the name is Sadalmelik (or Sadalmelek), although rarely used today. [12] [13]