HD 18438
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cepheus |
| HD 18438 | |
| Right ascension | 03h 06m 07.84053s |
| Declination | +79° 25′ 06.7270″ |
| Apparent magnitude (V) | +5.49 |
| TYC 4516-2148-1 | |
| Right ascension | 03h 06m 06.49835s |
| Declination | +79° 25′ 03.7722″ |
| Apparent magnitude (V) | +9.08 |
| Characteristics | |
| HD 18438 | |
| Evolutionary stage | AGB |
| Spectral type | M2.5 III |
| B−V color index | +1.569 |
| Variable type | suspected |
| TYC 4516-2148-1 | |
| Evolutionary stage | subgiant |
| Spectral type | F7 IV |
| B−V color index | +0.61 |
| Astrometry | |
| HD 18438 | |
| Radial velocity (Rv) | −37.6 km/s |
| Proper motion (μ) | RA: −35.523 mas/yr Dec.: +10.383 mas/yr |
| Parallax (π) | 4.2470±0.0776 mas |
| Distance | 770 ± 10 ly (235 ± 4 pc) |
| Absolute magnitude (MV) | -1.0 |
| TYC 4516-2148-1 | |
| Proper motion (μ) | RA: −35.639 mas/yr Dec.: +10.069 mas/yr |
| Parallax (π) | 4.3427 ± 0.0176 mas |
| Distance | 751 ± 3 ly (230.3 ± 0.9 pc) |
| Absolute magnitude (MV) | 2.5 |
| Orbit | |
| Primary | HD 18438 |
| Companion | TYC 4516-2148-1 |
| Semi-major axis (a) | 4.7" (1100 AU) |
| Details | |
| 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 | |
| ADS 2294, CCDM J03061+7925, WDS J03061+7925 | |
| HD 18438: AG+79°95, BD+78°103, FK5 105, GC 3638, HD 18438, HIP 14417, HR 881, SAO 4810, PPM 5183, TIC 297820335, TYC 4516-2147-1, 2MASS J03060788+7925066 | |
| TYC 4516-2148-1: TYC 4516-2148-1 | |
| Database references | |
| SIMBAD | HD 18438 |
| TYC 4516-2148-1 | |
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 red-hued dot of light about 10 degrees away from the celestial north pole. It is part of a wide binary system with an F-type subgiant star. 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.