27 Hydrae is a triple star system[5] system in the equatorial constellation of Hydra,[9] located 222 light years away from the Sun.[1] It is visible to the naked eye as a faint, orange-hued star with a combined apparent visual magnitude of 4.82.[2] The system is moving further from the Earth with a heliocentric radial velocity of +25.6 km/s.[6]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 20m 29.01857s[1] |
| Declination | −09° 33′ 20.5054″[1] |
| Apparent magnitude (V) | 4.818[2] (4.91 + 7.03 + 10.99)[3] |
| Characteristics | |
| Spectral type | K0III[4] + F4V + K2V[5] |
| Astrometry | |
| Radial velocity (Rv) | +25.60±0.13[6] km/s |
| Proper motion (μ) | RA: −12.48[1] mas/yr Dec.: −27.37[1] mas/yr |
| Parallax (π) | 14.66 ± 0.31 mas[1] |
| Distance | 222 ± 5 ly (68 ± 1 pc) |
| Details | |
| A | |
| Mass | 2.17[2] M☉ |
| Radius | 11[6] R☉ |
| Luminosity | 57.5[2] L☉ |
| Surface gravity (log g) | 2.9[6] cgs |
| Temperature | 4,965±26[2] K |
| Metallicity [Fe/H] | −0.07[6] dex |
| Rotational velocity (v sin i) | 3.3[6] km/s |
| Age | 1.91[2] Gyr |
| B | |
| Radius | 1.82[7] R☉ |
| Luminosity | 5.885[7] L☉ |
| Temperature | 6,664[7] K |
| C | |
| Radius | 0.72[8] R☉ |
| Luminosity | 0.227[8] L☉ |
| Temperature | 4,685[8] K |
| Other designations | |
| A: 27 Hya, BD−08°2643, HD 80586, HIP 45811, HR 3709, SAO 136768 | |
| B: BD−09°2801, HD 80550, HIP 45802, SAO 136767 | |
| C: TYC 5463-1518-1 | |
| Database references | |
| SIMBAD | data |
| B | |
| C | |
The magnitude 4.91[5] primary, component A, is an aging giant star with a stellar classification of K0 III.[4] It is a red clump giant,[10] which indicates it is on the horizontal branch and is generating energy through helium fusion at its core. The star is 1.9[2] billion years old with 2.17[2] times the mass of the Sun. It has swelled to 11[6] times the Sun's radius and is radiating 57.5[2] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,965 K.[2] The star is suspected to host a low-mass companion.[11]
The stellar companions to this star, designated components B and C, lie at an angular separation of 229.10″ from the primary, and form a binary pair with a separation of 9.20″ as of 2015.[3] The brighter member of the pair, component B, is a seventh magnitude F-type main-sequence star with a class of F4 V, while its companion is an eleventh magnitude K-type main-sequence star with a class of K2 V.[5]
Substellar companion
editThe Okayama Planet Search team published a paper in late 2008 reporting investigations into radial velocity variations observed for a set of evolved stars, showing hints of a substellar companion orbiting the primary member of the wide binary system 27 Hydrae.[11] Its orbital period is estimated at 9.3 years, but no planet has been confirmed yet.
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (unconfirmed) | ≥10 MJ | ≈5.9 | 3,400 | — | — | — |
References
edit- ^ a b c d e f 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.
- ^ a b c d e f g h i j Luck, R. Earle (2015). "Abundances in the Local Region. I. G and K Giants". Astronomical Journal. 150 (3). 88. arXiv:1507.01466. Bibcode:2015AJ....150...88L. doi:10.1088/0004-6256/150/3/88. S2CID 118505114.
- ^ a b Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466, Bibcode:2001AJ....122.3466M, doi:10.1086/323920, retrieved 2015-07-22
- ^ a b Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars". Michigan Spectral Survey. 5. Bibcode:1999MSS...C05....0H.
- ^ a b c d Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869–879. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
- ^ a b c d e f g Massarotti, Alessandro; et al. (January 2008). "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity". The Astronomical Journal. 135 (1): 209–231. Bibcode:2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209. S2CID 121883397.
- ^ a b c 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.
- ^ a b c 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.
- ^ a b "27 Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved May 3, 2019.
- ^ Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329, Bibcode:2000ApJ...539..732A, doi:10.1086/309278, S2CID 16673121
- ^ a b Toyota, Eri; et al. (2008). "Radial Velocity Search for Extrasolar Planets in Visual Binary Systems". Publications of the Astronomical Society of Japan. 61 (1): 19–28. Bibcode:2009PASJ...61...19T. doi:10.1093/pasj/61.1.19. hdl:20.500.14094/90001422.