15 Sagittae
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagitta |
| Right ascension | 20h 04m 06.22091s |
| Declination | +17° 04′ 12.6774″ |
| Apparent magnitude (V) | 5.80 |
| Characteristics | |
| Evolutionary stage | main sequence |
| Spectral type | G0V + L4 |
| B−V color index | 0.600±0.005 |
| Astrometry | |
| 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 |
| Orbit | |
| 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 | |
| 15 Sge A | |
| Mass | 1.08±0.04 M☉ |
| Radius | 1.115±0.021 R☉ |
| Luminosity | 1.338±0.032 L☉ |
| Surface gravity (log g) | 4.42±0.06 cgs |
| Temperature | 5,883±59 K |
| Metallicity [Fe/H] | 0.05±0.07 dex |
| Rotation | 17.5±2.3 |
| Rotational velocity (v sin i) | 4.42±0.06 km/s |
| Age | 2.5±1.8 Gyr |
| 15 Sge B | |
| Mass | 68.7+2.4 −3.1 MJup |
| Radius | 1.0±0.4 RJup |
| Luminosity | 0.000075±0.000016 L☉ |
| Temperature | 1,510–1,850 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 | |
| Database references | |
| SIMBAD | data |
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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. 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.
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, it 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.