Astronomy:Epsilon Aquilae
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| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Aquila |
| Right ascension | 18h 59m 37.356s[1] |
| Declination | +15° 04′ 05.81″[1] |
| Apparent magnitude (V) | +4.02[2] |
| Characteristics | |
| Spectral type | K1-IIICN0.5[3] |
| U−B color index | +1.04[2] |
| B−V color index | +1.08[2] |
| R−I color index | +0.52 |
| Astrometry | |
| Radial velocity (Rv) | −45.9±0.3[4] km/s |
| Proper motion (μ) | RA: −51.062[1] mas/yr Dec.: −69.439[1] mas/yr |
| Parallax (π) | 18.1821 ± 0.3319[1] mas |
| Distance | 179 ± 3 ly (55 ± 1 pc) |
| Absolute bolometric magnitude (Mbol) | +0.30[5] |
| Orbit[6] | |
| Period (P) | 1,270.6±1.1 d |
| Semi-major axis (a) | ≥ 86.9 ± 2.3 Gm (0.581 ± 0.015 astronomical unit|AU) |
| Eccentricity (e) | 0.272±0.026 |
| Periastron epoch (T) | 41718±17 MJD |
| Argument of periastron (ω) (secondary) | 82±5° |
| Semi-amplitude (K1) (primary) | 5.17±0.13 km/s |
| Details | |
| ε Aql Aa | |
| Mass | 2.1+0.4 −0.2[7] M☉ |
| Radius | 10.13+0.21 −0.22[8] R☉ |
| Luminosity | 54±5[9] L☉ |
| Surface gravity (log g) | 2.91[9] cgs |
| Temperature | 4,760[9] K |
| Metallicity [Fe/H] | 0.00[9] dex |
| Rotational velocity (v sin i) | 4.4[10] km/s |
| ε Aql Ab | |
| Mass | 0.47±0.05[7] M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
Epsilon Aquilae is a binary star[12] system in the equatorial constellation of Aquila, near the western constellation boundary with Hercules. Its name is a Bayer designation that is Latinized from ε Aquilae, and abbreviated Epsilon Aql or ε Aql. The system has an apparent visual magnitude of 4.02[2] and is visible to the naked eye. Based upon an annual parallax of 18.1821 mas,[1] Epsilon Aquilae lies at a distance of approximately 179 light-years (55 parsecs) from Earth, but is drifting closer with a radial velocity of −46 km/s.[4]
It has the traditional name Deneb el Okab /ˈdɛnɛb ɛl ˈoʊkæb/, from an Arabic term ذنب العقاب ðanab al-ʽuqāb "the tail of the eagle", and the Mandarin names Woo /ˈwuː/ and Yuë /ˈjuːeɪ/, derived from and represent the state Wú (吳), an old state was located at the mouth of the Yangtze River, and Yuè (越), an old state in Zhejiang province[13] (together with 19 Capricorni in Twelve States asterism). According to the R.H. Allen's works, it shares names with ζ Aquilae.[14] Epsilon Aquilae could be more precisely called Deneb el Okab Borealis, because is situated to the north of Zeta Aquilae, which can therefore be called Deneb el Okab Australis.[15]
Properties
The binary nature of this system was reported by German astronomer F. Kustner in 1914, but it was not confirmed until 1974. It is a single-lined spectroscopic binary system;[7] the pair orbit each other over a period of 1,271 days (3.5 years) with an eccentricity (ovalness) of 0.27.[6] There are two visual companions to Epsilon Aquilae, both reported by German astronomer R. Engelmann in 1887. Component B is a magnitude 10.56 star at an angular separation of 122.00″ along a position angle (PA) of 184° relative to the primary, as of 2014. At magnitude 11.25, component C is at a separation of 142.90″ with a PA of 159°, as of 2015.[16]
The primary component of this system is an evolved giant star with a stellar classification of K1-III CN0.5,[3] showing a mild overabundance of the CN molecule in the spectrum. The chemical abundances of the star suggest it has gone through first dredge-up.[17] It has more than double the mass of the Sun[7] and has expanded to ten times the Sun's radius.[8] The star shines with 54 times the Sun's luminosity, which is being radiated from its outer envelope at an effective temperature of 4,760 K.[9] At this heat, it glows with the orange-hue of a K-type star.[18]
This has been designated a barium star, meaning its atmosphere is extremely enriched with barium and other heavy elements. However, this is disputed, with astronomer Andrew McWilliam (1990) finding normal abundances from an s-process.[7]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 2.0 2.1 2.2 2.3 Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99): 99, Bibcode: 1966CoLPL...4...99J.
- ↑ 3.0 3.1 Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series 71: 245, doi:10.1086/191373, Bibcode: 1989ApJS...71..245K.
- ↑ 4.0 4.1 Famaey, B. et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics 430 (1): 165–186, doi:10.1051/0004-6361:20041272, Bibcode: 2005A&A...430..165F.
- ↑ Luck, R. Earle; Heiter, Ulrike (June 2007), "Giants in the Local Region", The Astronomical Journal 133 (6): 2464–2486, doi:10.1086/513194, Bibcode: 2007AJ....133.2464L.
- ↑ 6.0 6.1 Griffin, R. F. (June 1982), "Spectroscopic binary orbits from photoelectric radial velocities. Paper 44: epsilon Aquilae", The Observatory 102: 82–85, Bibcode: 1982Obs...102...82G.
- ↑ 7.0 7.1 7.2 7.3 7.4 Pourbaix, D.; Boffin, H. M. J. (February 2003), "Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component", Astronomy and Astrophysics 398 (3): 1163–1177, doi:10.1051/0004-6361:20021736, Bibcode: 2003A&A...398.1163P.
- ↑ 8.0 8.1 Baines, Ellyn K.; Clark, James H.; Kingsley, Bradley I.; Schmitt, Henrique R.; Stone, Jordan M. (2025-05-07), "Vintage NPOI: New and Updated Angular Diameters for 145 Stars" (in en), The Astronomical Journal 169 (6): 293, doi:10.3847/1538-3881/adc930, ISSN 1538-3881, Bibcode: 2025AJ....169..293B.
- ↑ 9.0 9.1 9.2 9.3 9.4 Piau, L. et al. (February 2011), "Surface convection and red-giant radius measurements", Astronomy and Astrophysics 526: A100, doi:10.1051/0004-6361/201014442, Bibcode: 2011A&A...526A.100P.
- ↑ 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, doi:10.1088/0004-6256/135/1/209, Bibcode: 2008AJ....135..209M.
- ↑ "eps Aql". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=eps+Aql.
- ↑ Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society 389 (2): 869–879, doi:10.1111/j.1365-2966.2008.13596.x, Bibcode: 2008MNRAS.389..869E.
- ↑ (in Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name , Hong Kong Space Museum. Accessed on line November 23, 2010.
- ↑ "Aquila, the Eagle", Star Names, Their Lore and Meaning (Dover): p. 61, 1963, https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Aquila*.html, retrieved 2025-04-15.
- ↑ "Deneb el Okab Borealis", STARS, http://stars.astro.illinois.edu/sow/denebokabb.html, retrieved 2025-04-15
- ↑ Mason, B. D. et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal 122 (6): 3466–3471, doi:10.1086/323920, Bibcode: 2001AJ....122.3466M.
- ↑ Mishenina, T. V. et al. (October 1995), "Chemical composition of five giants with positive CN-indices", Astronomy and Astrophysics Supplement 113: 333, Bibcode: 1995A&AS..113..333M.
- ↑ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16.
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