Epsilon Aquilae
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| 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 mas/yr[1] Dec.: −69.439 mas/yr[1] |
| Parallax (π) | 18.1821±0.3319 mas[1] |
| 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 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 | 10.14±0.70[8] R☉ |
| Luminosity | 54±5[8] L☉ |
| Surface gravity (log g) | 2.91[8] cgs |
| Temperature | 4,760[8] K |
| Metallicity [Fe/H] | 0.00[8] dex |
| Rotational velocity (v sin i) | 4.4[9] km/s |
| ε Aql Ab | |
| Mass | 0.47±0.05[7] M☉ |
| Other designations | |
| Deneb el Okab, ε Aql, 13 Aql, BD+14 3736, FK5 712, GC 26091, HD 176411, HIP 93244, HR 7176, SAO 104318, PPM 135586, WDS J18596+1504A[10] | |
| Database references | |
| SIMBAD | data |
Epsilon Aquilae is a binary star[11] 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[12] (together with 19 Capricorni in Twelve States asterism). According to the R.H. Allen's works, it shares names with ζ Aquilae.[13] 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.[14]
Properties
[edit]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.[15]
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.[16] It has more than double[7] the mass of the Sun and has expanded to ten[8] times the Sun's radius. The star shines with 54–fold the Sun's luminosity, which is being radiated from its outer envelope at an effective temperature of 4,760 K.[8] At this heat, it glows with the orange-hue of a K-type star.[17]
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
[edit]- ^ a b c d e 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.
- ^ a b c d 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.
- ^ a b Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
- ^ a b 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, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272, S2CID 17804304.
- ^ Luck, R. Earle; Heiter, Ulrike (June 2007), "Giants in the Local Region", The Astronomical Journal, 133 (6): 2464–2486, Bibcode:2007AJ....133.2464L, doi:10.1086/513194.
- ^ a b 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.
- ^ a b c d e 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, arXiv:astro-ph/0211483, Bibcode:2003A&A...398.1163P, doi:10.1051/0004-6361:20021736, S2CID 12361870.
- ^ a b c d e f g Piau, L.; et al. (February 2011), "Surface convection and red-giant radius measurements", Astronomy and Astrophysics, 526: A100, arXiv:1010.3649, Bibcode:2011A&A...526A.100P, doi:10.1051/0004-6361/201014442, S2CID 118533297.
- ^ 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, S2CID 121883397.
- ^ "eps Aql". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2011-12-29.
- ^ 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, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
- ^ (in Chinese) English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Archived August 10, 2010, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ^ Allen, R. H. (1963), "Aquila, the Eagle", Star Names, Their Lore and Meaning, Dover, p. 61, retrieved 2025-04-15.
- ^ Kaler, James, "Deneb el Okab Borealis", STARS, retrieved 2025-04-15
- ^ 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.
- ^ 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, archived from the original on 2012-03-18, retrieved 2012-01-16.
