15 Sagittae (15 Sge) is a star in the northern constellation Sagitta, located around 550 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. 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. In 2002, the cause of this was found to be brown dwarf companion B via direct imaging.
Epoch J2000.0 Equinox J2000.0
|Right ascension||20h 04m 06.22091s|
|Declination||+17° 04′ 12.6774″|
|Apparent magnitude (V)||5.80|
|Evolutionary stage||main sequence|
|Spectral type||G0V + L4|
|B−V color index||0.600±0.005|
|Radial velocity (Rv)||4.57±0.1 km/s|
|Proper motion (μ)|| RA: −387.590 mas/yr |
Dec.: −419.542 mas/yr
|Parallax (π)||56.426 ± 0.069 mas|
|Distance||57.80 ± 0.07 ly |
(17.72 ± 0.02 pc)
|Absolute magnitude (MV)||4.55|
|Semi-major axis (a)||18.3+0.4|
|15 Sge A|
|Surface gravity (log g)||4.42±0.06 cgs|
|Metallicity [Fe/H]||0.05±0.07 dex|
|Rotational velocity (v sin i)||4.42±0.06 km/s|
|15 Sge B|
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, 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.
- 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.
- 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.
- 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. 97.
- 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.
- "15 Sge". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-24.
- 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.
- "Brown dwarf found around nearby sun-like star" (Press release). Kamuela, Hawaii: W. M. Keck Observatory. January 1, 2002. Retrieved August 13, 2019.
- 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.