Upsilon1_Hydrae
Upsilon1 Hydrae
Star in the constellation Hydra
Upsilon1 Hydrae (υ1 Hydrae, abbreviated Ups1 Hya, υ1 Hya), also named Zhang,[6] is a yellow-hued star in the constellation of Hydra. It is visible to the naked eye, having an apparent visual magnitude of 4.12.[2] Based upon an annual parallax shift of 12.36 mas as seen from Earth,[1] it is located about 264 light-years from the Sun. The star is moving closer to the Sun with a radial velocity of −14.34 km/s.[4] In 2005 it was announced that it had a substellar companion.[7]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 51m 28.69384s[1] |
| Declination | −14° 50′ 47.7710″ |
| Apparent magnitude (V) | 4.12[2] |
| Characteristics | |
| Spectral type | G6/8III[3] |
| U−B color index | +0.65[2] |
| B−V color index | +0.92[2] |
| Astrometry | |
| Radial velocity (Rv) | −14.34[4] km/s |
| Proper motion (μ) | RA: +18.88[1] mas/yr Dec.: −21.85[1] mas/yr |
| Parallax (π) | 12.36 ± 0.26 mas[1] |
| Distance | 264 ± 6 ly (81 ± 2 pc) |
| Absolute magnitude (MV) | −0.43[5] |
| Details[4] | |
| Mass | 3.33 M☉ |
| Radius | 14.69 R☉ |
| Luminosity | 162 L☉ |
| Surface gravity (log g) | 2.95 cgs |
| Temperature | 5,185 K |
| Metallicity [Fe/H] | 0.10 dex |
| Rotational velocity (v sin i) | 2.11 km/s |
| Age | 270 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
υ1 Hydrae (Latinised to Upsilon1 Hydrae) is the star's Bayer designation.
In Chinese, 張宿 (Zhāng Sù), meaning Extended Net, refers to an asterism consisting of Upsilon1 Hydrae, Lambda Hydrae, Mu Hydrae, HD 87344, Kappa Hydrae and Phi1 Hydrae.[8] Consequently, Upsilon1 Hydrae itself is known as 張宿一 (Zhāng Sù yī), "the First Star of Extended Net".[9] In 2016, the International Astronomical Union (IAU) organized a Working Group on Star Names (WGSN)[10] to catalog and standardize proper names for stars. The WGSN approved the name Zhang for this star on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.[6]
With a stellar classification of G6/8 III,[3] Upsilon1 Hydrae is an evolved G-type giant star. It has an estimated 3.3 times the mass of the Sun and has expanded to 14.7 times the Sun's radius. The star is about 270 million years old with a projected rotational velocity of just 2.11 km/s. It is radiating 162 times the Sun's luminosity from its photosphere at an effective temperature of 5,185 K.[4]
Substellar companion
The Okayama Planet Search team published a paper in 2005 reporting investigations on radial velocity variations observed for a set of class G giants and announcing the detection of a brown dwarf companion in orbit around Upsilon1 Hydrae.[7] The orbital period for this companion is roughly 4.1 years, and it has a high eccentricity of 0.57. Since the inclination of the orbit to the line-of-sight is unknown, only a lower bound on the mass can be determined. It has at least 49 times the mass of Jupiter.[7]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥49 MJ | 3.9 | 1,500 | 0.57 | — | — |
- 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.
- Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
- Takeda; et al. (2008). "Stellar Parameters and Elemental Abundances of Late-G Giants". Publications of the Astronomical Society of Japan. 60 (4): 781–802. arXiv:0805.2434. Bibcode:2008PASJ...60..781T. doi:10.1093/pasj/60.4.781. S2CID 16258166.
- Jofré, E.; et al. (2015), "Stellar parameters and chemical abundances of 223 evolved stars with and without planets", Astronomy & Astrophysics, 574: A50, arXiv:1410.6422, Bibcode:2015A&A...574A..50J, doi:10.1051/0004-6361/201424474, S2CID 53666931.
- 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, S2CID 119257644.
- "Naming Stars". IAU.org. Retrieved 16 December 2017.
- Sato; et al. (2005). "Radial-Velocity Variability of G-Type Giants: First Three Years of the Okayama Planet Search Program". Publications of the Astronomical Society of Japan. 57 (1): 97–107. Bibcode:2005PASJ...57...97S. doi:10.1093/pasj/57.1.97.
- (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
- (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
- "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.