15 Sagittae
G-type main sequence star in the constellation Sagitta
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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.[1] 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.[8] In 2002, the cause of this was found to be brown dwarf companion B via direct imaging.[9]
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| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagitta[1] |
| Right ascension | 20h 04m 06.22077s[2] |
| Declination | +17° 04â² 12.6766â³[2] |
| Apparent magnitude (V) | 5.80[1] |
| Characteristics | |
| Evolutionary stage | main sequence[2] |
| Spectral type | G0V + L4[3] |
| BâV color index | 0.600±0.005[1] |
| Astrometry | |
| Radial velocity (Rv) | 4.57±0.1[4] km/s |
| Proper motion (μ) | RA: â387.472[2] mas/yr Dec.: â419.497[2] mas/yr |
| Parallax (Ï) | 56.2724±0.0094 mas[5] |
| Distance | 57.960 ± 0.010 ly (17.771 ± 0.003 pc) |
| Absolute magnitude (MV) | 4.55[1] |
| Orbit[5] | |
| Period (P) | 63.77+0.63 â0.61 yr |
| Semi-major axis (a) | 16.88±0.10 AU |
| Eccentricity (e) | 0.4683+0.0032 â0.0031 |
| Inclination (i) | 97.73±0.31° |
| Longitude of the node (Ω) | 330.88±0.21° |
| Periastron epoch (T) | 2,457,070±11 |
| Argument of periastron (Ï) (secondary) | 266.23±0.45° |
| Details[5] | |
| 15 Sge A | |
| Mass | 1.114±0.013 Mâ |
| Radius | 1.051±0.010 Râ |
| Luminosity | 1.224±0.043 Lâ |
| Surface gravity (log g) | 4.442±0.010 cgs |
| Temperature | 5,932±81 K |
| Metallicity [Fe/H] | +0.051±0.057 dex |
| Rotation | 14.8±1.3 days |
| Rotational velocity (v sin i) | 4.42±0.06[3] km/s |
| Age | 2.26±0.40 Gyr |
| 15 Sge B | |
| Mass | 75.39±0.67 MJup |
| Radius | 0.82+0.10 â0.07[6] RJup |
| Luminosity | 0.000075±0.000016[3] Lâ |
| Temperature | 1,510â1,850[3] 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[7] | |
| Database references | |
| SIMBAD | data |
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,[10] 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]
John Flamsteed labelled this star as z Sagittae, but the designation was dropped by later authors and is now largely unknown.[11]