Astronomy:HR 3750
Coordinates: 
09h 27m 46.7799s, −06° 04′ 16.2822″
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Hydra[1] |
| Right ascension | 09h 27m 46.7799s[2] |
| Declination | −06° 04′ 16.282″[2] |
| Apparent magnitude (V) | 5.40[citation needed] |
| Characteristics | |
| Evolutionary stage | subgiant[3] |
| Spectral type | G1.5IV-V[4] |
| Apparent magnitude (G) | 5.1625[5] |
| Astrometry | |
| Radial velocity (Rv) | +54.93±0.21[6] km/s |
| Proper motion (μ) | RA: −242.6±0.4[5] mas/yr Dec.: −52.7±0.3[5] mas/yr |
| Parallax (π) | 32.30 ± 0.36[5] mas |
| Distance | 101 ± 1 ly (31.0 ± 0.3 pc) |
| Absolute magnitude (MV) | A:2.76; B:4.28[3] |
| Orbit[6] | |
| Period (P) | 34.53±0.16 years |
| Semi-major axis (a) | 0.4089±0.0079″ |
| Eccentricity (e) | 0.366±0.022 |
| Inclination (i) | 85.4±0.0° |
| Longitude of the node (Ω) | 150.42±0.39° |
| Periastron epoch (T) | 2,455,083±211 JD |
| Argument of periapsis (ω) (primary) | 347.5±6.7° |
| Semi-amplitude (K1) (primary) | 5.42±0.17 km/s |
| Semi-amplitude (K2) (secondary) | 6.30±0.25 km/s |
| Details[6] | |
| HD 81809 A | |
| Mass | 0.87±0.08 M☉ |
| Radius | 1.95±0.08 R☉ |
| Luminosity | 3.44±0.43 L☉ |
| Luminosity (bolometric) | 5.8±0.3[7] L☉ |
| Surface gravity (log g) | 3.7981±0.0054 cgs |
| Temperature | 5,619±125 K |
| Metallicity [Fe/H] | −0.49±0.14 dex |
| Rotation | 40.2[7] days |
| Rotational velocity (v sin i) | 2.0±1.5 km/s |
| Age | 9.75±1.78 Gyr |
| HD 81809 B | |
| Mass | 0.83±0.01 M☉ |
| Radius | 1.12±0.03 R☉ |
| Luminosity | 1.31±0.10 L☉ |
| Surface gravity (log g) | 4.2776±0.0027 cgs |
| Temperature | 5,833±72 K |
| Metallicity [Fe/H] | −0.23±0.06 dex |
| Age | 11.1±1.5 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
HR 3750 is a binary star system in the equatorial constellation of Hydra at a distance of 101 light years. This object is visible to the naked eye as a dim, white star with an apparent visual magnitude of 5.4. It is receding from the Earth with a heliocentric radial velocity of 57.9±0.2 km/s.[5] This binary is unusual because its eruptions[clarification needed] do not seem to conform to the Waldmeier effect—i.e. the strongest eruptions of HR 3750 are not the ones characterized by the fast eruption onset.[8] Kinematically, the binary belongs to the thick disk of the Milky Way galaxy—a population of ancient, metal-poor stars.[3]
The star system is a spectroscopic binary with a 32 year, nearly edge-on orbit. The primary, HD 81809 A's visual magnitude is 5.610±0.005 while the secondary, HD 81809 B's visual magnitude is 7.115±0.015. The larger star, HD 81809 A, has been hypothetised to have engulfed a 0.36 M☉ red dwarf star 1–3 billion years ago to explain its unusually older age than expected from theorethical models,[3] but the age discrepancy has been resolved as of 2026[update] with newer data, discarding the need of a stellar merger. The secondary component, however, appears to be more metal-enriched than the primary, which is unexpected for stars that presumably formed in the same envoirment. This indicates that component B had its metallicity changed after a collision with (metal-enriched) planetesimals.[6]
HD 81809 A[7] has a well defined chromospheric activity cycle with a period of 7.3±1.5 years.[9]
References
- ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific 99 (617): 695. doi:10.1086/132034. Bibcode: 1987PASP...99..695R Constellation record for this object at VizieR.
- ↑ 2.0 2.1 2.2 "HD 81809". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+81809.
- ↑ 3.0 3.1 3.2 3.3 Fuhrmann, Klaus; Chini, Rolf (2018), "Fossil Merger of a Population II Star", The Astrophysical Journal 858 (2): 103, doi:10.3847/1538-4357/aabaff, Bibcode: 2018ApJ...858..103F
- ↑ Keenan, Philip C.; McNeil, Raymond C. (October 1989). "The Perkins Catalog of Revised MK Types for the Cooler Stars". Astrophysical Journal Supplement 71: 245. doi:10.1086/191373. Bibcode: 1989ApJS...71..245K.
- ↑ 5.0 5.1 5.2 5.3 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.
- ↑ 6.0 6.1 6.2 6.3 Di Mauro, Maria Pia; Pezzotti, Camilla; Moedas, Nuno; Catanzaro, Giovanni; Maxted, Pierre F. L.; Corsaro, Enrico; Reda, Raffaele; Scuflaire, Richard et al. (2026-03-16). "On the Contradictory Case of the Binary System HD 81809 Hosting Two Pulsating Solar-like Stars Observed by TESS". The Astrophysical Journal 1000 (1): 92. doi:10.3847/1538-4357/ae40ad. ISSN 0004-637X.
- ↑ 7.0 7.1 7.2 Egeland, Ricky (2018), "Deconvolving the HD 81809 Binary: Rotational and Activity Evidence for a Subgiant with a Sun-like Cycle", The Astrophysical Journal 866 (2): 80, doi:10.3847/1538-4357/aadf86, Bibcode: 2018ApJ...866...80E
- ↑ Garg, Suyog; Karak, Bidya Binay; Egeland, Ricky; Soon, Willie; Baliunas, Sallie (2019), "Waldmeier Effect in Stellar Cycles", The Astrophysical Journal 886 (2): 132, doi:10.3847/1538-4357/ab4a17, Bibcode: 2019ApJ...886..132G
- ↑ Orlando, S.; Favata, F.; Micela, G.; Sciortino, S.; Maggio, A.; Schmitt, J. H. M. M.; Robrade, J.; Mittag, M. (2017), "Fifteen years in the high-energy life of the solar-type star HD 81809", Astronomy & Astrophysics 605: A19, doi:10.1051/0004-6361/201731301
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