91 Aquarii

91 Aquarii is the Flamsteed designation for a triple star[7] system in the equatorial constellation of Aquarius. It also bears the Bayer designation Psi1 Aquarii (ψ1 Aqr, ψ1 Aquarii). It is visible to the naked eye with an apparent visual magnitude of +4.248.[2] Parallax measurements yield an estimated distance of around 150 light-years (46 parsecs) from Earth.[1] An extrasolar planet is known to orbit the main star.

91 Aquarii
Location of ψ1 Aquarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Aquarius
Right ascension  23h 15m 53.49482s[1]
Declination –9° 05′ 15.8546″[1]
Apparent magnitude (V) +4.248[2]
Characteristics
Spectral type K1 III[3]
U−B color index +1.035[2]
B−V color index +1.104[2]
R−I color index 0.56[4]
Astrometry
Radial velocity (Rv)−25.49±0.74[5] km/s
Proper motion (μ) RA: +368.78[1] mas/yr
Dec.: –17.16[1] mas/yr
Parallax (π)21.77 ± 0.29[1] mas
Distance150 ± 2 ly
(45.9 ± 0.6 pc)
Absolute magnitude (MV)0.919[6]
Details
Mass1.38±0.29[3] M☉
Radius10.96±0.21[3] R☉
Luminosity54.3±3.1[3] L☉
Surface gravity (log g)2.6[5] cgs
Temperature4730±68[3] K
Metallicity [Fe/H]–0.14[5] dex
Rotational velocity (v sin i)2.9[5] km/s
Age2.98±1.63[3] Gyr
Other designations
Psi1 Aquarii, ADS 16633, Gl 893.2, WDS J23159-0905
A: BD–09 6156, FK5 1608, HD 219449, HIP 114855, HR 8841, LTT 9437, SAO 146598
BC: BD–09 6155, HD 219430, LTT 9434, SAO 146596
Database references
SIMBADA
BC

Stellar system

91 Aquarii is a triple star system.[7] The primary component, 91 Aqr A, is a giant star with a stellar classification of K1 III.[3] This is an evolved star with 138% of the Sun's mass that has expanded to over 10 times the size of the Sun.[3] It is radiating 54[3] times the Sun's luminosity from its outer envelope at an effective temperature of 4,730 K.[3] This gives it the orange-hued glow of a K-type star.[8]

The primary shares a common proper motion with two others stars, 91 Aqr B and C, suggesting that they are physically connected.[9] The latter pair form a binary system located at an angular separation of 52 arcseconds from the primary.[10] They are 10th magnitude stars separated by 0.3 arcseconds from each other.

Component Apparent
magnitude
(V)		 Spectral
type
A4.22K0 III
B9.62K3 V
C10.10

Because it lies near the same line of sight, the binary star system CCDM J23159-0905DE was listed to belong to the 91 Aquarii system according to the CCDM catalogue. However, it is listed as physically unconnected in the WDS catalogue and the pair have a different proper motion than 91 Aquarii.[9] CCDM J23159-0905DE has two components, the 13th magnitude CCDM J23159-0905D 80.4 arcseconds from 91 Aquarii, and the 14th magnitude CCDM J23159-0905E 19.7 arcseconds from 91 Aquarii.

Planetary system

In 2003, the discovery of an extrasolar planet orbiting 91 Aquarii A was announced.[11] Despite controversy, the exoplanet was confirmed again on Jan 03, 2011 by the Conference " Planetary Systems Beyond the Main Sequence", Bamberg 2010 (Quirrenbach et al.). The 91 Aquarii b is listed as "confirmed" as in 2020.[12]

The 91 Aquarii planetary system[13]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b >3.2 MJ 0.70 181.4±0.1 0.027±0.026 — —
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See also

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. Baines, Ellyn K.; et al. (2018). "Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer". The Astronomical Journal. 155. 30. arXiv:1712.08109. Bibcode:2018AJ....155...30B. doi:10.3847/1538-3881/aa9d8b.
  4. VizieR Detailed Page for HR 8841, retrieved 2009-11-28.
  5. 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.
  6. Liu, Y. J.; et al. (2007), "The abundances of nearby red clump giants", Monthly Notices of the Royal Astronomical Society, 382 (2): 553–66, Bibcode:2007MNRAS.382..553L, doi:10.1111/j.1365-2966.2007.11852.x.
  7. 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.
  8. "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.
  9. Roell, T.; Neuhäuser, R.; Seifahrt, A.; Mugrauer, M. (June 2012), "Extrasolar planets in stellar multiple systems", Astronomy & Astrophysics, 542: A92, arXiv:1204.4833, Bibcode:2012A&A...542A..92R, doi:10.1051/0004-6361/201118051
  10. Buscombe, W. (1962), "Spectral classification of Southern fundamental stars", Mount Stromlo Observatory Mimeogram, 4, Bibcode:1962MtSOM...4....1B.
  11. Mitchell, D. S.; S. Frink; A. Quirrenbach; D. A. Fischer; G. W. Marcy; R. P. Butler (2004-01-05). "Four Substellar Companions Found Around K Giant Stars". Bulletin of the American Astronomical Society, 35#5; AAS 203rd Meeting; Session 17 Extra Solar Planets. Retrieved 2009-11-28.
  12. openexoplanetcatalogue.com 91 Aquarii
  13. Mitchell, David S.; et al. (2013). "Precise radial velocities of giant stars". Astronomy and Astrophysics. 555. A87. arXiv:1305.5107. Bibcode:2013A&A...555A..87M. doi:10.1051/0004-6361/201321714.

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