Epsilon Aquarii

Epsilon Aquarii, Latinized from ε Aquarii, is a binary star in the equatorial zodiac constellation of Aquarius, located near the western constellation border with Capricornus. It has the proper name Albali /ælˈbeɪli/, now formally recognized by the IAU.^[11][12] It is visible to the naked eye with an apparent visual magnitude of 3.77,^[2] and has an absolute magnitude of −0.46.^[7] Based upon parallax measurements taken by the Gaia spacecraft, it is located at a distance of approximately 244 light-years (75 pc) from Earth.^[1] The star is drifting closer with a radial velocity of −20 km/s.^[1]

Epsilon Aquarii

Location of ε Aquarii (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquarius
Right ascension	20h 47m 40.54957s[1]
Declination	−09° 29′ 44.79693″[1]
Apparent magnitude (V)	3.77[2]
Characteristics
Evolutionary stage	Main sequence[3] or subgiant[4]
Spectral type	A1 V[2] + KV[4]
U−B color index	+0.029[5]
B−V color index	–0.001[5]
Variable type	Constant[6]
Astrometry
Radial velocity (Rv)	−19.82±0.58[1] km/s
Proper motion (μ)	RA: +33.923 mas/yr[1] Dec.: -34.926 mas/yr[1]
Parallax (π)	13.3619 ± 0.3737 mas[1]
Distance	244 ± 7 ly (75 ± 2 pc)
Absolute magnitude (MV)	−0.46[7]
Orbit[4]
Primary	A
Companion	B
Period (P)	1.2 years
Semi-major axis (a)	25.9 mas 1.7 AU
Details
A
Mass	2.98±0.03[3] M☉
Radius	4.2[4] R☉
Luminosity	161±9[8] L☉
Surface gravity (log g)	3.66±0.14[9] cgs
Temperature	9,622±327[9] K
Metallicity [Fe/H]	−0.08±0.35[6] dex
Rotational velocity (v sin i)	118.0±5.9[7] km/s
Age	388[9] Myr
B
Mass	0.61[4] M☉
Radius	0.57[4] R☉
Temperature	4,070[4] K
Other designations
Albali, ε Aqr, 2 Aquarii, BD–10°5506, FK5 781, HD 198001, HIP 102618, HR 7950, SAO 144810[10]
Database references
SIMBAD	data

The primary is an A-type main-sequence star with a stellar classification of A1 V.^[2] It is estimated to be estimated 388^[9] million years old with a high rate of spin, showing a projected rotational velocity of around 118 km/s.^[7] The elemental abundances in the stellar atmosphere are close to solar, with pronounced underabundances of aluminium and strontium.^[6] The star has three^[3] times the mass of the Sun and about 4.2^[4] times the Sun's radius. It is radiating 161^[8] times the luminosity of the Sun from its photosphere at an effective temperature of 9,622 K.^[9]

The secondary component is a K-type main-sequence star with 0.6 times the mass and 0.57 times the mass of the Sun. Located at a projected separation of 26 milliarcseconds from the primary, this translates to a physical separation of 1.7 astronomical units. Albali A and B complete an orbit around their center of mass each 1.2 years.^[4]

Nomenclature

ε Aquarii (Latinised to Epsilon Aquarii) is the star's Bayer designation.

It bore the traditional name, Albali, from the Arabic البالع (albāli‘), meaning "the swallower". (See also Albulaan.) Along with Mu Aquarii (Albulaan) and Nu Aquarii (also Albulaan), they were al Bulaʽ (البلع), meaning "the Swallower".^[13][14] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[15] to catalogue and standardize proper names for stars. The WGSN approved the name Albali for this star on 12 September 2016, and it is now so included in the List of IAU-approved Star Names.^[12]

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, it was designated Nir Saad Bula (نير سعد ألبلع nayyir sa'd al bulaʽ), which was translated into Latin as Lucida Fortunæ Dissipantis, meaning "the brightest of luck of the swallower".^[16]

In Chinese, 女宿 (Nǚ Sù), meaning Girl (asterism), refers to an asterism consisting of Epsilon Aquarii, Mu Aquarii, 4 Aquarii, 5 Aquarii and 3 Aquarii.^[17] Consequently, the Chinese name for Epsilon Aquarii itself is 女宿一 (Nǚ Sù yī, English: the First Star of Girl).^[18]

References

1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
2. Levato, O. H. (August 1972), "Rotational Velocities and Spectral Types of Some A-Type Stars", Publications of the Astronomical Society of the Pacific, 84 (500): 584, Bibcode:1972PASP...84..584L, doi:10.1086/129336.
3. Zorec, J.; Royer, F. (2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789.
4. Waisberg, Idel; Klein, Ygal; Katz, Boaz (2023-08-01). "Hidden Companions to Intermediate-mass Stars. VIII. Discovery of a 0.6 M ⊙, 1.7 au Companion to Albali = ϵ Aquarii". Research Notes of the American Astronomical Society. 7 (8): 163. Bibcode:2023RNAAS...7..163W. doi:10.3847/2515-5172/acebe1. ISSN 2515-5172.
5. Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars, 8: 59, Bibcode:1984SAAOC...8...59C.
6. Kocer, D.; et al. (August 2003), "Elemental abundance analyses with DAO spectrograms. XXVII. The superficially normal stars theta And (A2 IV), epsilon Del (B6 III), epsilon Aqr (A1.5 V), and iota And (B9 V)", Astronomy and Astrophysics, 406 (3): 975–980, Bibcode:2003A&A...406..975K, doi:10.1051/0004-6361:20030620.
7. Ammler-von Eiff, Matthias; Reiners, Ansgar (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: A116, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724, S2CID 53666672.
8. Baines, Ellyn K.; Blomquist, Solvay; Clark III, James H.; Gorney, Jim; Maier, Erin; Sanborn, Jason; Schmitt, Henrique R.; Stone, Jordan M.; van Belle, Gerard T.; Braun, Kaspar von (2023-01-09). "Simultaneous Six-way Observations from the Navy Precision Optical Interferometer". The Astronomical Journal. 165 (2): 41. Bibcode:2023AJ....165...41B. doi:10.3847/1538-3881/aca277. ISSN 0004-6256.
9. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
10. "* eps Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-06-29.
11. Kunitzsch, Paul; Smart, Tim (2006), A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.), Cambridge, Massachusetts: Sky Pub, ISBN 978-1-931559-44-7.
12. Naming Stars, IAU.org, retrieved 16 December 2017.
13. Davis Jr., G. A. (October 1944), "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names", Popular Astronomy, 52 (3): 12, Bibcode:1944PA.....52....8D.
14. Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 53, ISBN 0-486-21079-0, retrieved 2010-12-12.
15. IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
16. Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket", Monthly Notices of the Royal Astronomical Society, 55: 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429.
17. (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
18. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived October 25, 2008, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.

External links

• Image Epsilon Aquarii