21 Aquarii
{{short description|Star in the constellation Aquarius}}
{{Starbox begin}}
{{Starbox observe
| constell = Aquarius
| dec = {{DEC|-03|33|24.2964}}
}}
{{Starbox character
| u-b =
| variable =
}}
{{Starbox astrometry
| parallax = 7.8747
| p_error = 0.2182
}}
{{Starbox detail
| mass =
| radius = {{Val|28.01|1.09|2.12}}
| luminosity = {{Val|203.4|6.4}}
| temperature = {{Val|4119|165|78}}
| rotational_velocity =
| age_myr =
}}
{{Starbox catalog
| names={{odlist | BD=-04°5446 | FK5=3708 | HD=203926 | HIP=105767 | HR=8199 | SAO=145384 }}
}}
{{Starbox reference
| Simbad=21+Aqr
}}
{{Starbox end}}
21 Aquarii is a single star in the zodiac constellation of Aquarius. 21 Aquarii is the Flamsteed designation. It is visible to the naked eye as a dim, orange-hued star with an apparent visual magnitude of 5.49. This object is a member of the HR 1614 moving group, and is moving closer to the Earth with a heliocentric radial velocity of −24.5 km/s.
This object is an evolved giant star with a stellar classification of K4 III. As a result of having exhausted the hydrogen at its core, it has expanded to 27 times the radius of the Sun. The star is radiating 203 times the luminosity of the Sun from its swollen photosphere at an effective temperature of 4,120 K.
References
{{reflist|refs=
{{cite DR2|2684391775892287616}}
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| doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | arxiv=0806.2878
| bibcode=2008MNRAS.389..869E | s2cid=14878976 }}
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| title=Michigan catalogue of two-dimensional spectral types for the HD Stars
| journal=Michigan Spectral Survey
| volume=5 | year=1999
| bibcode=1999MSS...C05....0H }}
| title=General catalogue of stellar radial velocities
| journal=Carnegie Institute Washington D.C. Publication | last=Wilson | first=Ralph Elmer
| date=1953 | bibcode=1953GCRV..C......0W }}
| last1=McWilliam | first1=Andrew
| title=High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances
| journal=Astrophysical Journal Supplement Series
| volume=74 | pages=1075–1128 | date=December 1990
| doi=10.1086/191527 | bibcode=1990ApJS...74.1075M | doi-access=free }}
| title=First giant branch and asymptotic giant branch stars in nearby aggregates
| last1=Eggen | first1=Olin J. | last2=Iben | first2=Icko Jr.
| journal=Astronomical Journal
| volume=101 | pages=1377–1407 | date=April 1991
| doi=10.1086/115773 | bibcode=1991AJ....101.1377E }}.
}}
{{Stars of Aquarius}}
{{DEFAULTSORT:21 Aquarii}}
Category:Aquarius (constellation)