1 Aquarii
Binary star in the constellation Aquarius
From Wikipedia, the free encyclopedia
1 Aquarii, or WDS J20394+0029, is a binary star[5] system in the zodiac constellation of Aquarius, about 263 light years away from the Sun.[1] 1 Aquarii is its 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]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| 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 |
| Name | 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 | |
| 1 Aqr, BD−00°4064, FK5 3651, HD 196758, HIP 101936, HR 7897, SAO 126062, CCDM J20394+0029, WDS J20394+0029[10] | |
| Database references | |
| SIMBAD | data |
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 billion years old[7] 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 times the mass of the Sun[7] and has expanded to 11 times the Sun's radius.[8] It is radiating 53.7 times the Sun's luminosity[8] 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]
Etymology
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), now used for the star Alpha Aquarii.[12][13]