[ 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,[3] located a degree north of the celestial equator.[8] The system is moving closer to the Earth with a heliocentric radial velocity of −41 km/s.[8]]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 {{Convert|1966.7|days|years|disp=out}} and an eccentricity of 0.368.[8] The visible component is an aging giant star with a stellar classification of K1III.[5] At the age of 1.26[14] billion years old it is a red clump giant, which indicates it is on the horizontal branch and is generating energy through the helium fusion at its core.[4] The star has 1.5[14] times the mass of the Sun and has expanded to 11[15] times the Sun's radius. It is radiating 53.7[15] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,715 K.[17]
The mass of the companion appears small, suggesting a red dwarf no higher than class M5.[8] In addition to the spectroscopic companion there are two faint optical companions that have no physical relation to 1 Aqr.[37]
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.[3][4]
References
1. ^1 2 {{cite journal|doi=10.1051/0004-6361:20030163|title=The Wilson-Bappu effect: A tool to determine stellar distances|journal=Astronomy and Astrophysics|volume=401|issue=3|pages=997–1008|year=2003|last1=Pace|first1=G.|last2=Pasquini|first2=L.|last3=Ortolani|first3=S.|bibcode=2003A&A...401..997P|arxiv = astro-ph/0301637 }}
2. ^{{cite simbad | title=11 Per | access-date=2019-03-28 }}
3. ^[https://academic.oup.com/astrogeo/article/49/5/5.27/422591 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
4. ^[https://www.naic.edu/~gibson/starnames/starnames.html Star Names]; Arecebo Observatory website; mod.: Steve Gibson; accessed March 2019
5. ^1 2 3 4 {{cite journal | title=UBV Photometry of Equatorial Stars | last1=Cousins | first1=A. W. J. | journal=South African Astronomical Observatory Circulars | volume=8 | pages=69–84 | year=1984 | bibcode=1984SAAOC...8...69C }}
6. ^1 2 3 4 5 6 7 {{cite journal | title=Spectroscopic binary orbits from photoelectric radial velocities. Paper 239: HD 134169, HD 176526, 1 Aquarii, and HD 219420 | last1=Griffin | first1=R. F. | journal=The Observatory | volume=134 | pages=316–339 | year=2014 | bibcode=2014Obs...134..316G }}
7. ^1 2 {{cite journal | title=Abundances in the Local Region. I. G and K Giants | last1=Luck | first1=R. Earle | journal=Astronomical Journal | volume=150 | issue=3 | pages= | at=88 | year=2015 | arxiv=1507.01466 | bibcode=2015AJ....150...88L | doi=10.1088/0004-6256/150/3/88 }}Vizier catalog entry
8. ^1 2 {{cite journal | title=The Spectra of the Bright Stars of Types F5-K5 | last1=Roman | first1=Nancy G. | journal=Astrophysical Journal | volume=116 | pages=122–143 | year=1952 | bibcode=1952ApJ...116..122R | doi=10.1086/145598 }}
9. ^1 2 3 4 5 {{cite journal | bibcode=2016ApJ...817...40F | doi=10.3847/0004-637X/817/1/40 | arxiv=1511.04088 | title=Determining Ages of APOGEE Giants with Known Distances | journal=The Astrophysical Journal | volume=817 | pages=40 | year=2016 | last1=Feuillet | first1=Diane K. | last2=Bovy | first2=Jo | last3=Holtzman | first3=Jon | last4=Girardi | first4=Léo | last5=MacDonald | first5=Nick | last6=Majewski | first6=Steven R. | last7=Nidever | first7=David L. }}
10. ^1 2 3 4 {{citation | display-authors=1 | last1=Massarotti | first1=Alessandro | last2=Latham | first2=David W. | last3=Stefanik | first3=Robert P. | last4=Fogel | first4=Jeffrey | title=Rotational and Radial Velocities for a Sample of 761 Hipparcos Giants and the Role of Binarity | journal=The Astronomical Journal | volume=135 | issue=1 | pages=209–231 |date=January 2008 | doi=10.1088/0004-6256/135/1/209 | bibcode=2008AJ....135..209M }}
11. ^1 2 {{citation | last1=Alves | first1=David R. | title=K-Band Calibration of the Red Clump Luminosity | journal=The Astrophysical Journal | volume=539 | issue=2 | pages=732–741 | date=August 2000 | doi=10.1086/309278 | bibcode=2000ApJ...539..732A | arxiv=astro-ph/0003329 | postscript=. }}
12. ^1 {{citation | display-authors=1 | last1=Mason | first1=B. D. | last2=Wycoff | first2=G. L. | last3=Hartkopf | first3=W. I. | last4=Douglass | first4=G. G. | last5=Worley | first5=C. E. | title=The Washington Visual Double Star Catalog | year=2014 | bibcode=2001AJ....122.3466M | postscript=. | doi=10.1086/323920 | volume=122 | journal=The Astronomical Journal | pages=3466–3471}}