1 Aquarii

1 Aquarii is a binary star[5] system in the zodiac constellation of Aquarius, about 257 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]

1 Aquarii
Location of 1 Aqr (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 20h 39m 24.89343s[1]
Declination +00° 29′ 11.1326″[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±0.03[5] km/s
Proper motion (μ) RA: 96.075[1] mas/yr
Dec.: −8.722[1] mas/yr
Parallax (π)12.7097 ± 0.1722[1] mas
Distance257 ± 3 ly
(79 ± 1 pc)
Absolute magnitude (MV)0.77[6]
Orbit[5]
Primary1 Aquarii A
Companion1 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
Mass1.50±0.43[7] M☉
Radius11[8] R☉
Luminosity53.7[8] L☉
Surface gravity (log g)2.63±0.11[7] cgs
Temperature4715±15[9] K
Metallicity−0.12[6]
Rotational velocity (v sin i)1.8[6] km/s
Age1.26[7] Gyr
Other designations
1 Aqr, BD+0°4064, FK5 3651, HD 196758, HIP 101936, HR 7897, SAO 126062, CCDM J20394+0029, WDS J20394+0029[10]
Database references
SIMBADdata

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]

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), although rarely used today.[12][13]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Cousins, A. W. J. (1984). "UBV Photometry of Equatorial Stars". South African Astronomical Observatory Circulars. 8: 69–84. Bibcode:1984SAAOC...8...69C.
  3. Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329, Bibcode:2000ApJ...539..732A, doi:10.1086/309278, S2CID 16673121.
  4. Roman, Nancy G. (1952). "The Spectra of the Bright Stars of Types F5-K5". Astrophysical Journal. 116: 122–143. Bibcode:1952ApJ...116..122R. doi:10.1086/145598.
  5. Griffin, R. F. (2014). "Spectroscopic binary orbits from photoelectric radial velocities. Paper 239: HD 134169, HD 176526, 1 Aquarii, and HD 219420". The Observatory. 134: 316–339. Bibcode:2014Obs...134..316G.
  6. Pace, G.; Pasquini, L.; Ortolani, S. (2003). "The Wilson-Bappu effect: A tool to determine stellar distances". Astronomy and Astrophysics. 401 (3): 997–1008. arXiv:astro-ph/0301637. Bibcode:2003A&A...401..997P. doi:10.1051/0004-6361:20030163. S2CID 17029463.
  7. Feuillet, Diane K.; Bovy, Jo; Holtzman, Jon; Girardi, Léo; MacDonald, Nick; Majewski, Steven R.; Nidever, David L. (2016). "Determining Ages of APOGEE Giants with Known Distances". The Astrophysical Journal. 817 (1): 40. arXiv:1511.04088. Bibcode:2016ApJ...817...40F. doi:10.3847/0004-637X/817/1/40. S2CID 118675933.
  8. Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 Hipparcos Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209
  9. Luck, R. Earle (2015). "Abundances in the Local Region. I. G and K Giants". Astronomical Journal. 150 (3). 88. arXiv:1507.01466. Bibcode:2015AJ....150...88L. doi:10.1088/0004-6256/150/3/88. S2CID 118505114.Vizier catalog entry
  10. "11 Per". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-28.
  11. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
  12. A Llnguist's Angle on the Star of Bethlehem — i.e. α Aquarii; Coates, Richard; Astronomy & Geophysics, Volume 49, Issue 5; (01 October 2008); Pp. 5.27–5.32; https://doi.org/10.1111/j.1468-4004.2008.49527.x
  13. Star Names; Arecebo Observatory website; mod.: Steve Gibson; accessed March 2019
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