HD 98618 is a yellow-hued 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.[2] Based on measurements, this star is located at a distance of 135 light years from the Sun based on parallax,[1] and is drifting further away with a radial velocity of +7.1 km/s.[2] 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.[6]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 11h 21m 29.0695s[1] |
| Declination | +58° 29′ 03.7043″[1] |
| Apparent magnitude (V) | 7.65[2] |
| Characteristics | |
| Spectral type | G5V[2] |
| B−V color index | 0.642±0.007[2] |
| Astrometry | |
| Radial velocity (Rv) | +7.10±0.09[2] km/s |
| Proper motion (μ) | RA: 41.329±0.057[1] mas/yr Dec.: 28.415±0.076[1] mas/yr |
| Parallax (π) | 24.2400 ± 0.0486 mas[1] |
| Distance | 134.6 ± 0.3 ly (41.25 ± 0.08 pc) |
| Absolute magnitude (MV) | 4.78±0.09[3] |
| Details[4] | |
| Mass | 1.04±0.15 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 |
| Other designations | |
| Database references | |
| SIMBAD | data |
The stellar classification of HD 98618 is G5V,[2] 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.[6] 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).[7] 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 star appears roughly the same age as the Sun,[6] although the level of chromospheric activity suggests it may be older.[7] 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.[4]
References
edit- ^ a b c d e f 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.
- ^ a b c d e f g 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.
- ^ 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.
- ^ a b 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.
- ^ a b c 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.
- ^ a b 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.