HD 98618
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 11h 21m 29.0695s |
| Declination | +58° 29′ 03.7043″ |
| Apparent magnitude (V) | 7.65 |
| Characteristics | |
| Spectral type | G5V |
| B−V color index | 0.642±0.007 |
| Astrometry | |
| Radial velocity (Rv) | +7.10±0.09 km/s |
| Proper motion (μ) | RA: 41.329±0.057 mas/yr Dec.: 28.415±0.076 mas/yr |
| Parallax (π) | 24.2400±0.0486 mas |
| Distance | 134.6 ± 0.3 ly (41.25 ± 0.08 pc) |
| Absolute magnitude (MV) | 4.78±0.09 |
| Orbit | |
| Period (P) | 790+280 −150 yr |
| Semi-major axis (a) | 100+22 −13 au |
| Eccentricity (e) | 0.34+0.30 −0.23 |
| Inclination (i) | 55+5 −13° |
| Details | |
| A | |
| Mass | 1.138+0.057 −0.056 M☉ |
| Radius | 1.034±0.037 R☉ |
| Luminosity | 1.10+0.19 −0.16 L☉ |
| Surface gravity (log g) | 4.37 cgs |
| Temperature | 5,812 K |
| Metallicity [Fe/H] | 0.03 dex |
| Rotational velocity (v sin i) | 2.1 km/s |
| Age | 4.9+2.6 −2.9 Gyr |
| B | |
| Mass | 0.470+0.030 −0.029 M☉ |
| Other designations | |
| BD+59°1369, HD 98618, HIP 55459, SAO 27996 | |
| Database references | |
| SIMBAD | data |
HD 98618 is a binary star in the northern circumpolar constellation of Ursa Major. It is invisible to the naked eye, having an apparent visual magnitude of just 7.65. Based on parallax measurements, this system is located at a distance of 135 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +7.1 km/s. It is a likely member of the thin disk population and is orbiting the Milky Way at about the same distance from the Galactic Center as the Sun.
The stellar classification of HD 98618 A is G5V, which matches an ordinary G-type main-sequence star that is generating energy through hydrogen fusion in the core region. It is almost identical in most respects to the Sun; it has therefore been proposed as a candidate solar twin. However, like the solar twin 18 Scorpii, HD 98618 has a lithium abundance significantly higher than that of the Sun ([Li/H] = +0.45 ± 0.08). Meléndez & Ramírez (2007) have suggested that HD 98618 be considered a "quasi solar twin", since they have now identified a solar twin, HIP 56948, with lithium content identical within the observational error to the Sun's.
The companion was identified in 2020 with data from the Gaia spacecraft. It has a mass of 0.470 solar masses. The two components orbit around each other with a period of roughly 800 years and a semi-major axis of 100 astronomical units.
The star appears roughly the same age as the Sun, although the level of chromospheric activity suggests it may be older. It is rotating with a leisurely projected rotational velocity of 2.1 km/s. The mass and size of the star are a few percent higher than the Sun. It is radiating around 10% more luminosity than the Sun from its photosphere at an effective temperature of 5,812 K.
References
- 1 2 3 4 5 6 7 8 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.
- 1 2 3 4 5 6 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.
- ↑ Porto de Mello, G. F.; et al. (March 2014). "A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun; I. Atmospheric parameters and color similarity to the Sun". Astronomy and Astrophysics. 563: A52. arXiv:1312.7571. Bibcode:2014A&A...563A..52P. doi:10.1051/0004-6361/201322277. S2CID 119111150.
- 1 2 3 4 An, Qier; Brandt, Timothy D.; Brandt, G. Mirek; Venner, Alexander (October 2025). "Orbits and Masses for 156 Companions from Combined Astrometry and Radial Velocities, and a Validation of Gaia Non-single-star Solutions". The Astrophysical Journal Supplement Series. 280 (2): 61. arXiv:2508.08374. Bibcode:2025ApJS..280...61A. doi:10.3847/1538-4365/adfa99. ISSN 0067-0049.
- 1 2 Valenti, Jeff A.; Fischer, Debra A. (July 2005). "Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs". The Astrophysical Journal Supplement Series. 159 (1): 141–166. Bibcode:2005ApJS..159..141V. doi:10.1086/430500.
- ↑ "HD 98618". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-10-13.
- 1 2 3 Meléndez, J.; et al. (2006). "HD 98618: A Star Closely Resembling Our Sun". The Astrophysical Journal. 641 (2): L133–L136. arXiv:astro-ph/0603219. Bibcode:2006ApJ...641L.133M. doi:10.1086/503898. S2CID 17479387.
- 1 2 Meléndez, J.; Ramírez, I. (2007). "HIP 56948: A Solar Twin with a Low Lithium Abundance". The Astrophysical Journal. 669 (2): L89–L92. arXiv:0709.4290. Bibcode:2007ApJ...669L..89M. doi:10.1086/523942. S2CID 15952981.
- ↑ Hartman, Zachary D.; Lépine, Sébastien (2020-04-01). "The SUPERWIDE Catalog: A Catalog of 99,203 Wide Binaries Found in Gaia and Supplemented by the SUPERBLINK High Proper Motion Catalog". The Astrophysical Journal Supplement Series. 247 (2): 66. arXiv:2002.08850. doi:10.3847/1538-4365/ab79a6. ISSN 0067-0049.
