Astronomy:HD 98618
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Ursa Major[1] |
| Right ascension | 11h 21m 29.0695s[2] |
| Declination | +58° 29′ 03.7043″[2] |
| Apparent magnitude (V) | 7.65[1] |
| Characteristics | |
| Spectral type | G5V[1] |
| B−V color index | 0.642±0.007[1] |
| Astrometry | |
| Radial velocity (Rv) | +7.10±0.09[1] km/s |
| Proper motion (μ) | RA: 41.329±0.057[2] mas/yr Dec.: 28.415±0.076[2] mas/yr |
| Parallax (π) | 24.2400 ± 0.0486[2] mas |
| Distance | 134.6 ± 0.3 ly (41.25 ± 0.08 pc) |
| Absolute magnitude (MV) | 4.78±0.09[3] |
| Orbit[4] | |
| 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[5] | |
| A | |
| Mass | 1.138+0.057 −0.056[4] 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[4] M☉ |
| Other designations | |
| 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.[1] Based on parallax measurements, this system is located at a distance of 135 light years from the Sun based on parallax,[2] and is drifting further away with a radial velocity of +7.1 km/s.[1] 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.[7]
The stellar classification of HD 98618 A is G5V,[1] 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.[7] 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).[8] 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.[9] 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.[4]
The star appears roughly the same age as the Sun,[7] although the level of chromospheric activity suggests it may be older.[8] 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.[5]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 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.
- ↑ 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. doi:10.1051/0004-6361/201322277. Bibcode: 2014A&A...563A..52P.
- ↑ 4.0 4.1 4.2 4.3 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" (in en). The Astrophysical Journal Supplement Series 280 (2): 61. doi:10.3847/1538-4365/adfa99. ISSN 0067-0049. Bibcode: 2025ApJS..280...61A.
- ↑ 5.0 5.1 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. doi:10.1086/430500. Bibcode: 2005ApJS..159..141V.
- ↑ "HD 98618". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+98618.
- ↑ 7.0 7.1 7.2 Meléndez, J. et al. (2006). "HD 98618: A Star Closely Resembling Our Sun". The Astrophysical Journal 641 (2): L133–L136. doi:10.1086/503898. Bibcode: 2006ApJ...641L.133M.
- ↑ 8.0 8.1 Meléndez, J.; Ramírez, I. (2007). "HIP 56948: A Solar Twin with a Low Lithium Abundance". The Astrophysical Journal 669 (2): L89–L92. doi:10.1086/523942. Bibcode: 2007ApJ...669L..89M.
- ↑ 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. doi:10.3847/1538-4365/ab79a6. ISSN 0067-0049.
External links
Coordinates: 
11h 21m 29s, +58° 53′ 18″
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