26 Aquilae

26 Aquilae (abbreviated 26 Aql) is a binary star system in the equatorial constellation of Aquila. 20 Aquilae is its Flamsteed designation though it also bears the Bayer designation f Aquilae. It has an apparent visual magnitude of 5.00,[2] which means it is faintly visible to the naked eye. As the Earth orbits the Sun, this star system undergoes a parallax shift of 21.15 mas.[1] This means it is located at a distance of approximately 154 light-years (47 parsecs) from Earth, give or take a 3 light-year margin of error.

26 Aquilae
Location of 26 Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension  19h 20m 32.90437s[1]
Declination –05° 24′ 56.7440″[1]
Apparent magnitude (V) 5.00[2]
Characteristics
Spectral type G8 III-IV[3]
U−B color index +0.634[2]
B−V color index +0.936[2]
R−I color index 0.5
Astrometry
Radial velocity (Rv)−16.91±1.93[4] km/s
Proper motion (μ) RA: +113.13[1] mas/yr
Dec.: +46.20 [1] mas/yr
Parallax (π)21.15 ± 0.39[1] mas
Distance154 ± 3 ly
(47.3 ± 0.9 pc)
Orbit[4]
Period (P)266.544 days
Eccentricity (e)0.833
Semi-amplitude (K1)
(primary)		29.86 km/s
Details
26 Aquilae A
Mass3.2+0.2
−0.2[5] M☉
Radius6[4] R☉
Luminosity21[4] L☉
Surface gravity (log g)3.2[4] cgs
Temperature4940[5] K
Metallicity [Fe/H]–0.21[4] dex
Rotational velocity (v sin i)1.3[4] km/s
26 Aquilae B
Mass1.4±0.05[5] M☉
Other designations
f Aquilae, BD–05° 4936, FK5 3544, HD 181391, HIP 95066, HR 7333, SAO 143286.[6]
Database references
SIMBADdata

This is a single-lined spectroscopic binary system, meaning that the presence of an orbiting companion is revealed through shifts in the spectrum of the primary star. The pair orbit each other with a period of 266.544 days at a high eccentricity of 0.833.[4] Little is known about this companion, although its mass can be estimated as 140% of the mass of the Sun.

The primary component has a stellar classification of G8 III-IV.[3] The luminosity class of III-IV indicates the spectrum resembles that of a star part way between the subgiant and giant stages of its evolution. It has more than three[5] times the mass of the Sun and six[4] times the Sun's radius. It is radiating 21[4] times as much luminosity as the Sun from this enlarged outer envelope at an effective temperature of 4940 K.[5] At this heat, the star glows with the characteristic yellow hue of a G-type star.[7]

References
  1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society, 172: 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667.
  3. 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.
  4. 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.
  5. 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: 1163–1177, arXiv:astro-ph/0211483, Bibcode:2003A&A...398.1163P, doi:10.1051/0004-6361:20021736.
  6. "f Aql". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-22.
  7. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on February 22, 2012, retrieved 2012-01-16
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