| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Apus |
| Right ascension | 15h 35m 39.921s[1] |
| Declination | −80° 12′ 16.54″[1] |
| Apparent magnitude (V) | 8.70[2] |
| Characteristics | |
| Evolutionary stage | subgiant |
| Spectral type | K2IV[3] or K0/K1V[4] |
| B−Vcolor index | 0.891±0.017[5] |
| Astrometry | |
| Radial velocity (Rv) | +26.01±0.0327[1] km/s |
| Proper motion (μ) | RA: −49.570[1]mas/yr Dec.: 41.135[1]mas/yr |
| Parallax (π) | 24.6722±0.0327 mas[1] |
| Distance | 132.2 ± 0.2 ly (40.53 ± 0.05 pc) |
| Absolute magnitude (MV) | 5.75[5] |
| Details[6] | |
| Mass | 0.930+0.024 −0.035 M☉ |
| Radius | 0.86±0.01 R☉ |
| Luminosity | 0.528[1] L☉ |
| Surface gravity (log g) | 4.449±0.434 cgs |
| Temperature | 5,297±20 K |
| Metallicity [Fe/H] | +0.29 dex |
| Rotational velocity (v sin i) | 2.207±0.356 km/s |
| Age | 2.991+2.629 −1.902 Gyr |
| Other designations | |
| Karaka,NSV 7116,CPD–79°844,Gaia DR2 5778418870846853888,HD 137388,HIP 76351,2MASS J15353994-8012164[7] | |
| Database references | |
| SIMBAD | data |
HD 137388 is an orange-huedstar in the southernconstellation ofApus. It has the proper nameKaraka, after the native New Zealandkaraka tree. The name was assigned by representatives ofNew Zealand in theIAU'sNameExoWorlds contest.[8] The star is too faint to be visible to the naked eye, having anapparent visual magnitude of 8.70.[2] It is located at a distance of 132 light years from theSun based onparallax. The star is drifting further away with aradial velocity of +26 km/s, having come as close as 52.9 light-years some 1.2 million years ago.[5] It has anabsolute magnitude of 5.75.[5]
Thestellar classification of HD 137388 is K2IV,[3] matching that of anevolvingsubgiant star. However, in 2011 Dumusque and colleagues found a class of K0/K1V, suggesting it is instead aK-type main-sequence star.[4] It is around three billion years old and is spinning with aprojected rotational velocity of 2.2 km/s.[6] The star shows amagnetic activity cycle, similar to thesolar cycle.[4] It has 93% of themass of the Sun and 86% of theSun's radius. Based on the abundance of iron in thespectrum, it is a highmetallicity star with a greater abundance of heavy elements compared to the Sun. The star is radiating 53% of theluminosity of the Sun from itsphotosphere at aneffective temperature of 5,297 K.[6]
Radial velocity studies indicate that it has a planet, originally named HD 137388 b (mass 0.223 MJ, period 330d). It orbits at a typical distance of 0.89 AU with an eccentricity of 0.36,[4][9] completely overlapping the star'shabitable zone.[10] The planet was officially designatedKererū, theMāori name of theNew Zealand pigeon, by theIAU in the same contest that named its parent star.[8]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b (Kererū) | 0.223±0.029 MJ | 0.89±0.02 | 330.0±4.0 | 0.36±0.12 | 86.0±35.0° | — |
