HD 181720
HD 181720 is an 8th magnitude G-type main sequence star located approximately 190 light years away in the constellation Sagittarius. This star is larger, hotter, brighter, and less massive than our Sun. Also its metal content is three-tenths as much as the Sun.
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 22m 52.99s[1] |
| Declination | –32° 55′ 08.6″[1] |
| Apparent magnitude (V) | 7.84[2] |
| Characteristics | |
| Spectral type | G1V[2] |
| Apparent magnitude (B) | 8.44 |
| Apparent magnitude (J) | 6.652 |
| Apparent magnitude (H) | 6.346 |
| Apparent magnitude (K) | 6.294 |
| V−R color index | 0.599[2] |
| Astrometry | |
| Radial velocity (Rv) | -45.404 km/s |
| Proper motion (μ) | RA: 88.154 mas/yr Dec.: -415.038 mas/yr |
| Parallax (π) | 16.5816 ± 0.0664[3] mas |
| Distance | 196.7 ± 0.8 ly (60.3 ± 0.2 pc) |
| Absolute magnitude (MV) | 4.10[2] |
| Details | |
| Mass | 0.92[2] M☉ |
| Radius | 1.39[2] R☉ |
| Luminosity | 1.94[2] L☉ |
| Surface gravity (log g) | 4.24 ± 0.15[2] cgs |
| Temperature | 5781 ± 18[2] K |
| Metallicity | -0.53 ± 0.02[2] |
| Rotation | 47 days |
| Rotational velocity (v sin i) | 1.5[2] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
| Extrasolar Planets Encyclopaedia | data |
The star HD 181720 is named Sika. The name was selected in the NameExoWorlds campaign by Ghana, during the 100th anniversary of the IAU. Sika means gold in the Ewe language.[4][5]
Planetary system
In 2009, a gas giant planet was found in orbit around the star. It was named "Toge" in 2019. The planets around such metal-poor stars are rare (only three known similar cases are HD 111232, HD 114762, and HD 22781).[6]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (Toge) | ≥0.37 MJ | 1.78 | 956 ± 14 | 0.26 ± 0.06 | — | — |
References
- van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Vizier catalog entry
- Santos, N. C.; et al. (2010). "The HARPS search for southern extrasolar planets XXI. Three new giant planets orbiting the metal-poor stars HD5388, HD181720, and HD190984". Astronomy and Astrophysics. 512. A47. arXiv:0912.3216. Bibcode:2010A&A...512A..47S. doi:10.1051/0004-6361/200913489. S2CID 118675798.
- 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.
- "Approved names". NameExoworlds. Retrieved 2020-01-02.
- "International Astronomical Union | IAU". www.iau.org. Retrieved 2020-01-02.
- Adibekyan, Vardan (2019), "HEAVY METAL RULES. I. EXOPLANET INCIDENCE AND METALLICITY", Geosciences, 9 (3): 105, arXiv:1902.04493, doi:10.3390/geosciences9030105, S2CID 119089419
- Santos, N. C.; Mayor, M.; Bonfils, X.; Dumusque, X.; Bouchy, F.; Figueira, P.; Lovis, C.; Melo, C.; Pepe, F.; Queloz, D.; Ségransan, D.; Sousa, S. G.; Udry, S. (2011), The HARPS search for southern extrasolar planets XXV. Results from the metal-poor sample, arXiv:1011.2094, doi:10.1051/0004-6361/201015494, S2CID 119106340
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