Astronomy:15 Sagittae
250px 15 Sagittae and its companion Credit: Keck Observatory | |
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Sagitta[1] |
| Right ascension | 20h 04m 06.22077s[2] |
| Declination | +17° 04′ 12.6766″[2] |
| Apparent magnitude (V) | 5.80[1] |
| Characteristics | |
| Evolutionary stage | main sequence[2] |
| Spectral type | G0V + L4[3] |
| B−V color index | 0.600±0.005[1] |
| Astrometry | |
| Radial velocity (Rv) | 4.57±0.1[4] km/s |
| Proper motion (μ) | RA: −387.472[2] mas/yr Dec.: −419.497[2] mas/yr |
| Parallax (π) | 56.2724 ± 0.0094[5] mas |
| 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 −0.61 yr |
| Semi-major axis (a) | 16.88±0.10 astronomical unit|AU |
| Eccentricity (e) | 0.4683+0.0032 −0.0031 |
| Inclination (i) | 97.73±0.31° |
| Longitude of the node (Ω) | 330.88±0.21° |
| Periastron epoch (T) | 2,457,070±11 JD |
| Argument of periastron (ω) (secondary) | 266.23±0.45° |
| Details[5] | |
| 15 Sge A | |
| Mass | 1.114±0.013 M☉ |
| Radius | 1.051±0.010 R☉ |
| Luminosity | 1.224±0.043 L☉ |
| 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 | 0.81+0.09 −0.08[6] RJup |
| Luminosity | 6.46+0.62 −0.57×10−5[7] L☉ |
| Surface gravity (log g) | 5.46±0.09[6] cgs |
| Temperature | 1,544+26 −31[6] K |
| Rotational velocity (v sin i) | 45.0±0.5[8] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
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]
John Flamsteed labelled this star as z Sagittae, but the designation was dropped by later authors and is now largely unknown.[10]
Characteristics
The spectrum of 15 Sagittae matches a spectral class of G0V, with the luminosity class V indicating it is a main sequence star fusing atoms of hydrogen into helium at its core.[3] 15 Sagittae is a solar analog,[11] having 1.11 times the mass of the Sun, 1.05 times the Sun's radius, and 1.22 times the Sun's luminosity, and an effective temperature of 5,932 K.[5] This temperature also gives it the yellow hue typical of a G-type star.[12] The abundance of metals in the stellar atmosphere (metallicity) is also close to solar, with an iron-to-hydrogen abundance ratio equivalent to 12% of that found in the Sun.[5] The star's age is estimated at 2.26 billion years.[5]
Companion
15 Sagittae was the target of the first radial velocity survey from Lick Observatory, which found a drift due to a companion.[11] In 2002, the cause of this was found to be a brown dwarf companion, 15 Sagittae B, detected via direct imaging at the Keck telescope.[13]
15 Sagittae B is a high-mass brown dwarf of spectral class L4, making it a L dwarf.[3] It has a radius equivalent to 81% that of Jupiter, an effective temperature of 1,544 K (1,271 °C; 2,320 °F),[6] and a luminosity of 0.0000065 (6.5×10−5) times that of the Sun.[7] The brown dwarf has a cloudy atmosphere[6] and an elemental abundance similar to that of the host star. Its projected rotational velocity is 45 km/s, relatively fast for a brown dwarf, making it highly suitable for Doppler imaging.[8]
The brown dwarf orbits with a period of 63.8 years around the primary star, having a semi-major axis of 16.88 astronomical units, a moderate eccentricity of 0.468, and an inclination of 97.7° relative to Earth. Along with its orbit, its mass has been determined dynamically with direct imaging, radial velocity variations caused by its gravitational pull around the star, and by the astrometric shift it exerts in the star's proper motion measurements taken by the Hipparcos and Gaia spacecrafts over a 20-year timespan, yielding a value of 75 Jupiter masses. 15 Sagittae B therefore is part of a select group of brown dwarfs with masses, ages, and luminosities determined without relying on substellar evolution models, making it a useful object to test the accuracy of such models.[5] At the discovery, it was thought to have a semi-major axis of 14 AU and a circular orbit viewed from pole-on,[14] but these properties were later massively revised with more observations. It is now approaching the primary as viewed from Earth.[3]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A XHIP record for this object at VizieR.
- ↑ 2.0 2.1 2.2 2.3 2.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940 Gaia DR3 record for this source at VizieR.
- ↑ 3.0 3.1 3.2 3.3 3.4 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. doi:10.1088/0004-637X/751/2/97. 97. Bibcode: 2012ApJ...751...97C.
- ↑ Nidever, David L. et al. (August 2002). "Radial Velocities for 889 Late-Type Stars". The Astrophysical Journal Supplement Series 141 (2): 503–522. doi:10.1086/340570. Bibcode: 2002ApJS..141..503N.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Li, Yaguang; Liu, Michael C.; Dupuy, Trent J.; Huber, Daniel; Zhang, Jingwen; Hey, Daniel; Costa, R. R.; Larsen, Jens Reersted et al. (2026-04-21). "A Test of Substellar Evolutionary Models with High-precision Ages from Asteroseismology and Gyrochronology for the Benchmark System HR 7672AB". The Astrophysical Journal 1002 (1): 13. doi:10.3847/1538-4357/ae4bdb. ISSN 0004-637X. Bibcode: 2026ApJ..1002...13L.
- ↑ 6.0 6.1 6.2 6.3 6.4 Kasagi, Yui; Kawashima, Yui; Kawahara, Hajime; Kotani, Takayuki; Masuda, Kento; Ahn, Kyohoon; Guyon, Olivier; Hirano, Teruyuki et al. (2025-08-02). "Unveiling the Atmosphere of HR 7672 B from the Near-Infrared High-Resolution Spectrum Using REACH/Subaru". The Astronomical Journal 170 (4): 211. doi:10.3847/1538-3881/adf730. Bibcode: 2025AJ....170..211K.
- ↑ 7.0 7.1 Brandt, Timothy D.; Dupuy, Trent J.; Bowler, Brendan P. (2019-09-11). "Precise Dynamical Masses of Directly Imaged Companions from Relative Astrometry, Radial Velocities, and Hipparcos–Gaia DR2 Accelerations". The Astronomical Journal 158 (4): 140. doi:10.3847/1538-3881/ab04a8. ISSN 1538-3881. Bibcode: 2019AJ....158..140B.
- ↑ 8.0 8.1 Wang, Ji; Kolecki, Jared R.; Ruffio, Jean-Baptiste; Wang, Jason J.; Mawet, Dimitri; Baker, Ashley; Bartos, Randall; Blake, Geoffrey A. et al. (2022-03-25). "Retrieving the C and O Abundances of HR 7672 AB: A Solar-type Primary Star with a Benchmark Brown Dwarf". The Astronomical Journal 163 (4): 189. doi:10.3847/1538-3881/ac56e2. ISSN 0004-6256. Bibcode: 2022AJ....163..189W.
- ↑ "15 Sge". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=15+Sge.
- ↑ Wagman, Morton (2003). Lost Stars: Lost, Missing, and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas-Louis de Lacaille, John Flamsteed, and Sundry Others. McDonald & Woodward Publishing Company. ISBN 978-0-939923-78-6. https://books.google.com/books?id=TYLvAAAAMAAJ&q=7664. Retrieved 2025-11-16.
- ↑ 11.0 11.1 Cumming, Andrew et al. (December 1999). "The Lick Planet Search: Detectability and Mass Thresholds". The Astrophysical Journal 526 (2): 890–915. doi:10.1086/308020. Bibcode: 1999ApJ...526..890C.
- ↑ "The Colour of Stars". Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. December 21, 2004. http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html. Retrieved 2012-01-16.
- ↑ "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. doi:10.1086/339845. Bibcode: 2002ApJ...571..519L.
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