Astronomy:27 Hydrae
  | |
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| 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 | |
| Evolutionary stage | red clump[4] |
| Spectral type | K0III[5] + F4V + K2V[6] |
| Astrometry | |
| Radial velocity (Rv) | +25.60±0.13[7] km/s |
| Proper motion (μ) | RA: −12.48[1] mas/yr Dec.: −27.37[1] mas/yr |
| Parallax (π) | 14.66 ± 0.31[1] mas |
| Distance | 222 ± 5 ly (68 ± 1 pc) |
| Details | |
| A | |
| Mass | 2.17[2] M☉ |
| Radius | 11[7] R☉ |
| Luminosity | 57.5[2] L☉ |
| Surface gravity (log g) | 2.9[7] cgs |
| Temperature | 4,965±26[2] K |
| Metallicity [Fe/H] | −0.07[7] dex |
| Rotational velocity (v sin i) | 3.3[7] km/s |
| Age | 1.91[2] Gyr |
| B | |
| Radius | 1.82[8] R☉ |
| Luminosity | 5.885[8] L☉ |
| Temperature | 6,664[8] K |
| C | |
| Radius | 0.72[9] R☉ |
| Luminosity | 0.227[9] L☉ |
| Temperature | 4,685[9] 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 | |
27 Hydrae is a triple star system[6] in the equatorial constellation of Hydra,[10] 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.[7]
The magnitude 4.91[6] primary, component A, is an aging giant star with a stellar classification of K0 III.[5] It is a red clump giant,[4] 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[7] 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.[6]
Substellar companion candidate
The 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 (ADS 7311).[11] A later study revised the minimum mass of this candidate companion to 28 Jupiter masses, indicating that if it exists, it is a brown dwarf rather than a planet.[12]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| (unconfirmed) | ≥28 MJ | ≈5.9 | 3,400 | — | — | — |
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 Luck, R. Earle (2015). "Abundances in the Local Region. I. G and K Giants". Astronomical Journal 150 (3): 88. doi:10.1088/0004-6256/150/3/88. Bibcode: 2015AJ....150...88L.
- ↑ 3.0 3.1 Mason, B. D. et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal 122 (6): 3466, doi:10.1086/323920, Bibcode: 2001AJ....122.3466M, http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/wds, retrieved 2015-07-22
- ↑ 4.0 4.1 Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal 539 (2): 732–741, doi:10.1086/309278, Bibcode: 2000ApJ...539..732A
- ↑ 5.0 5.1 Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars". Michigan Spectral Survey 5. Bibcode: 1999MSS...C05....0H.
- ↑ 6.0 6.1 6.2 6.3 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. doi:10.1111/j.1365-2966.2008.13596.x. Bibcode: 2008MNRAS.389..869E.
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 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. doi:10.1088/0004-6256/135/1/209. Bibcode: 2008AJ....135..209M.
- ↑ 8.0 8.1 8.2 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G. Gaia DR2 record for this source at VizieR.
- ↑ 9.0 9.1 9.2 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G. Gaia DR2 record for this source at VizieR.
- ↑ 10.0 10.1 "27 Hya". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=27+Hya.
- ↑ 11.0 11.1 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. doi:10.1093/pasj/61.1.19. Bibcode: 2009PASJ...61...19T.
- ↑ Katoh, Noriyuki; Itoh, Yoichi; Sato, Bun’ei (August 1, 2018). "Search for companions in visual binary systems using precise radial-velocity measurements" (in en). Publications of the Astronomical Society of Japan 70 (4). doi:10.1093/pasj/psy054. ISSN 0004-6264. https://academic.oup.com/pasj/article/doi/10.1093/pasj/psy054/5025942.
 |  |
