HD 18438
  | |
| Observation data Epoch J2000.0[1] Equinox J2000.0[1] | |
|---|---|
| Constellation | Centaurus |
| HD 18438 | |
| Right ascension | 03h 06m 07.84053s |
| Declination | +79° 25′ 06.7270″ |
| Apparent magnitude (V) | +5.49[1] |
| TYC 4516-2148-1 | |
| Right ascension | 03h 06m 06.49835s |
| Declination | +79° 25′ 03.7722″ |
| Apparent magnitude (V) | +9.08[1] |
| Characteristics | |
| HD 18438 | |
| Spectral type | M2.5 III |
| B−V color index | +1.569[2] |
| J−H color index | +0.864[1] |
| J−K color index | +1.145[1] |
| TYC 4516-2148-1 | |
| Spectral type | F7 IV[3] |
| B−V color index | +0.61 |
| Astrometry | |
| HD 18438 | |
| Radial velocity (Rv) | -37.6[1] km/s |
| Proper motion (μ) | RA: -35.523[1] mas/yr Dec.: 10.383[1] mas/yr |
| Parallax (π) | 4.443 ± 0.171[2] mas |
| Distance | 730 ± 30 ly (225 ± 9 pc) |
| Absolute magnitude (MV) | -1.0[4] |
| TYC 4516-2148-1 | |
| Proper motion (μ) | RA: -35.639[1] mas/yr Dec.: 10.069[1] mas/yr |
| Parallax (π) | 4.3427 ± 0.0176[1] mas |
| Distance | 751 ± 3 ly (230.3 ± 0.9 pc) |
| Absolute magnitude (MV) | 2.5[4] |
| Orbit[2] | |
| Primary | HD 18438 |
| Companion | TYC 4516-2148-1 |
| Semi-major axis (a) | 4.7[3]" (1100 AU) |
| Details[2] | |
| HD 18438 | |
| Mass | 1.84±0.09 M☉ |
| Radius | 88.475±4.424 R☉ |
| Luminosity | 929±41 L☉ |
| Surface gravity (log g) | 0.9±0.1 cgs |
| Temperature | 3860±100 K |
| Metallicity [Fe/H] | −0.4±0.1 dex |
| Rotation | 637 d |
| Rotational velocity (v sin i) | 5.5±0.2 km/s |
| Age | 5.5±2.4 Gyr |
| TYC 4516-2148-1 | |
| Mass | 1.174±0.184 M☉ |
| Radius | 2.554±0.182 R☉ |
| Luminosity | 7.558±0.095 L☉ |
| Surface gravity (log g) | 3.7±0.1 cgs |
| Temperature | 6164±211 K |
| Other designations | |
| HD 18438: BD+78°103, FK5 105, GC 3638, HD 18438, HIP 14417, HR 881, SAO 4810, PPM 5183, TYC 4516-2147-1, 2MASS J03060788+7925066[1] | |
| TYC 4516-2148-1: TYC 4516-2148-1[5] | |
| Database references | |
| SIMBAD | HD 18438 |
HD 18438 is a red giant star in the deep northern constellation of Cepheus, located about 730 light-years (220 parsecs) from Earth. With an apparent magnitude of 5.49, it is visible by the naked eye under dark skies as a reddish dot about 10 degrees away from the celestial north pole. It is part of a wide binary system with an F-type subgiant star designated TYC 4516-2148-1. In 2023, HD 18438 was discovered to be orbited by a 21 MJ substellar object, potentially making it the largest host star to an exoplanet ever found as of September 2024.[2][6]
Stellar characteristics[edit]
Binary system[edit]
Substellar companion[edit]
In 2023, a team of South Korean astronomers reported the discovery of a substellar object, named HD 18438 b, which could either be described as a massive gas giant exoplanet or a low-mass brown dwarf. It is about 8% larger than the planet Jupiter and 21 times as massive, the latter of which places it above the deuterium burning limit (~13 MJ[7]). It revolves around the star in a roughly circular (eccentricity 0.1) orbit with a semi-major axis of 2.1 AU (310,000,000 km) once every 803 days (2.20 years).
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 21 ± 1 MJ | 2.1 ± 0.1 | 803 ± 5 | 0.1 ± 0.1 | — | ~1.08[8] RJ |
References[edit]
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 "HD 18438". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-09-27.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Lee, Byeong-Cheol; et al. (2023-12-30). "A Search for Exoplanets around Northern Circumpolar Stars. VII. Detection of Planetary Companion Orbiting the Largest Host Star HD 18438". Journal of the Korean Astronomical Society. 56 (1): 35–40. arXiv:2303.08357. Bibcode:2023JKAS...56...35L. doi:10.5303/JKAS.2023.56.1.35.
- ↑ 3.0 3.1 Černis, K.; Meištas, E.; Straižys, V.; Jasevičius, V. (1989). "Photoelectric photometry of bright stars in the vicinity of the North Celestial Pole". Vilnius Astronomijos Observatorijos Biuletenis. 84: 9–20. Bibcode:1989VilOB..84....9C.
- ↑ 4.0 4.1 Bidelman, William P. (1958). "Spectral Classification of Visual Binaries Having Primaries Above the Main Sequence". Publications of the Astronomical Society of the Pacific. IOP Publishing. 70: 168. doi:10.1086/127203. ISSN 0004-6280.
- ↑ "TYC 4516-2148-1". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-09-27.
- ↑ "Planetary Systems". NASA Exoplanet Archive. NASA Exoplanet Science Institute. Retrieved 2024-09-27.
- ↑ "Exoplanet Criteria for Inclusion in the Archive". NASA Exoplanet Archive.
- ↑ "Exoplanet-catalog". Exoplanet Exploration: Planets Beyond our Solar System. Archived from the original on 4 June 2023. Retrieved 31 October 2023. Unknown parameter
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