15 Sagittae

15 Sagittae (15 Sge) is a star in the northern constellation Sagitta, located around 58 light years away from the Sun. It is visible to the naked eye as a faint, yellow-hued star with an apparent visual magnitude of 5.80.[2] Considered a solar analog, it was the target of the first radial velocity survey from Lick Observatory, which found a drift due to a companion.[6] In 2002, the cause of this was found to be brown dwarf companion B via direct imaging.[7]

15 Sagittae
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagitta
Right ascension 20h 04m 06.22091s[1]
Declination +17° 04′ 12.6774″[1]
Apparent magnitude (V) 5.80[2]
Characteristics
Evolutionary stage main sequence
Spectral type G0V + L4[3]
B−V color index 0.600±0.005[2]
Astrometry
Radial velocity (Rv)4.57±0.1[4] km/s
Proper motion (μ) RA: −387.590[1] mas/yr
Dec.: −419.542[1] mas/yr
Parallax (π)56.426 ± 0.069 mas[1]
Distance57.80 ± 0.07 ly
(17.72 ± 0.02 pc)
Absolute magnitude (MV)4.55[2]
Orbit[3]
Period (P)73.3+2.2
−3.9 yr
Semi-major axis (a)18.3+0.4
−0.5 AU
Eccentricity (e)0.50±0.01
Inclination (i)97.3+0.4
−0.5°
Details[3]
15 Sge A
Mass1.08±0.04 M☉
Radius1.115±0.021 R☉
Luminosity1.338±0.032 L☉
Surface gravity (log g)4.42±0.06 cgs
Temperature5,883±59 K
Metallicity [Fe/H]0.05±0.07 dex
Rotation17.5±2.3
Rotational velocity (v sin i)4.42±0.06 km/s
Age2.5±1.8 Gyr
15 Sge B
Mass68.7+2.4
−3.1 MJup
Radius1.0±0.4 RJup
Luminosity0.000075±0.000016 L☉
Temperature1,510–1,850 K
Other designations
15 Sge, BD+16°4121, GJ 779, HD 190406, HIP 98819, HR 7672, SAO 105635, LFT 1517, LHS 3515, LTT 15872, Wolf 866[5]
Database references
SIMBADdata

The companion is a high-mass substellar brown dwarf of spectral class L4 ± 1.5, only a few Jupiter masses below the limit for stars, in a long-period orbit around the primary star. Imaged by the Keck telescope, was the first brown dwarf candidate orbiting a sun-like star detected via imaging and is currently the only known companion brown dwarf which both has a significant radial velocity trend on the primary that has also been imaged.

The brown dwarf was originally thought to have a semi-major axis of 14 AU and a circular orbit viewed from pole-on,[8] but ten more years of observations found that the brown dwarf's orbit is viewed from nearly edge-on, is significantly eccentric and appeared to be moving in a circular orbit when first discovered, but is now approaching the primary as viewed from Earth.[3]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  3. Crepp, Justin R.; et al. (June 2012). "The Dynamical Mass and Three-Dimensional Orbit of HR7672B: A Benchmark Brown Dwarf with High Eccentricity". The Astrophysical Journal. 751 (2): 14. arXiv:1112.1725. Bibcode:2012ApJ...751...97C. doi:10.1088/0004-637X/751/2/97. S2CID 16113054. 97.
  4. Nidever, David L.; et al. (August 2002). "Radial Velocities for 889 Late-Type Stars". The Astrophysical Journal Supplement Series. 141 (2): 503–522. arXiv:astro-ph/0112477. Bibcode:2002ApJS..141..503N. doi:10.1086/340570. S2CID 51814894.
  5. "15 Sge". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-24.
  6. Cumming, Andrew; et al. (December 1999). "The Lick Planet Search: Detectability and Mass Thresholds". The Astrophysical Journal. 526 (2): 890–915. arXiv:astro-ph/9906466. Bibcode:1999ApJ...526..890C. doi:10.1086/308020. S2CID 12560512.
  7. "Brown dwarf found around nearby sun-like star" (Press release). Kamuela, Hawaii: W. M. Keck Observatory. January 1, 2002. Retrieved August 13, 2019.
  8. Liu, Michael C.; et al. (May 2002). "Crossing the Brown Dwarf Desert Using Adaptive Optics: A Very Close L-Dwarf Companion to the Nearby Solar Analog HR 7672". The Astrophysical Journal. 571 (1): 519–527. arXiv:astro-ph/0112407. Bibcode:2002ApJ...571..519L. doi:10.1086/339845. S2CID 11405638.
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