HR 3750
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra[1] |
| Right ascension | 09h 27m 46.7799s[2] |
| Declination | −06° 04′ 16.282″[2] |
| Apparent magnitude (V) | 5.40 |
| 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 mas/yr[5] Dec.: −52.7±0.3 mas/yr[5] |
| Parallax (π) | 32.30±0.36 mas[5] |
| 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 periastron (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 | |
| BD−05 2802, GJ 344, HD 81809, HIP 46404, HR 3750, SAO 136872, LTT 3482, 2MASS J09274680-0604164[2] | |
| 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 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 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. Bibcode:1987PASP...99..695R. doi:10.1086/132034. Constellation record for this object at VizieR.
- ^ a b c "HD 81809". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved June 21, 2021.
- ^ a b c d Fuhrmann, Klaus; Chini, Rolf (2018), "Fossil Merger of a Population II Star", The Astrophysical Journal, 858 (2): 103, Bibcode:2018ApJ...858..103F, doi:10.3847/1538-4357/aabaff, S2CID 125357563
- ^ Keenan, Philip C.; McNeil, Raymond C. (October 1989). "The Perkins Catalog of Revised MK Types for the Cooler Stars". Astrophysical Journal Supplement. 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
- ^ a b c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b c d Di Mauro, Maria Pia; Pezzotti, Camilla; Moedas, Nuno; Catanzaro, Giovanni; Maxted, Pierre F. L.; Corsaro, Enrico; Reda, Raffaele; Scuflaire, Richard; Bonanno, Alfio Maurizio; Giovannelli, Luca; Beck, Paul G. (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.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b c 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, arXiv:1807.10870, Bibcode:2018ApJ...866...80E, doi:10.3847/1538-4357/aadf86, S2CID 119537525
- ^ Garg, Suyog; Karak, Bidya Binay; Egeland, Ricky; Soon, Willie; Baliunas, Sallie (2019), "Waldmeier Effect in Stellar Cycles", The Astrophysical Journal, 886 (2): 132, arXiv:1909.12148, Bibcode:2019ApJ...886..132G, doi:10.3847/1538-4357/ab4a17, S2CID 202888617
- ^ 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, arXiv:1707.06437, doi:10.1051/0004-6361/201731301, S2CID 118843788