HD 137388

HD 137388 is an orange-hued star in the southern constellation of Apus. It has the proper name Karaka, after the native New Zealand karaka tree. The name was assigned by representatives of New Zealand in the IAU's NameExoWorlds contest.[8] The star is too faint to be visible to the naked eye, having an apparent visual magnitude of 8.70.[2] It is located at a distance of 132 light years from the Sun based on parallax. The star is drifting further away with a radial velocity of +26 km/s, having come as close as 52.9 light-years some 1.2 million years ago.[5] It has an absolute magnitude of 5.75.[5]

HD 137388 / Karaka
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−V color 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]
Distance132.2 ± 0.2 ly
(40.53 ± 0.05 pc)
Absolute magnitude (MV)5.75[5]
Details[6]
Mass0.930+0.024
−0.035 M☉
Radius0.86±0.01 R☉
Luminosity0.528[1] L☉
Surface gravity (log g)4.449±0.434 cgs
Temperature5,297±20 K
Metallicity [Fe/H]+0.29 dex
Rotational velocity (v sin i)2.207±0.356 km/s
Age2.991+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
SIMBADdata

The stellar classification of HD 137388 is K2IV,[3] matching that of an evolving subgiant star. However, in 2011 Dumusque and colleagues found a class of K0/K1V, suggesting it is instead a K-type main-sequence star.[4] It is around three billion years old and is spinning with a projected rotational velocity of 2.2 km/s.[6] The star shows a magnetic activity cycle, similar to the solar cycle.[4] It has 93% of the mass of the Sun and 86% of the Sun's radius. Based on the abundance of iron in the spectrum, it is a high metallicity star with a greater abundance of heavy elements compared to the Sun. The star is radiating 53% of the luminosity of the Sun from its photosphere at an effective temperature of 5,297 K.[6]

Planetary system

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's habitable zone.[10] The planet was officially designated Kererū, the Māori name of the New Zealand pigeon, by the IAU in the same contest that named its parent star.[8]

The HD 137388 planetary system[9]
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° —

References
  1. 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.
  2. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H.
  3. Gray, R. O.; et al. (2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637. S2CID 119476992.
  4. Dumusque, X.; et al. (2011). "The HARPS Search for Southern Extra-solar Planets. XXX. Planetary Systems around Stars with Solar-like Magnetic Cycles and Short-term Activity Variation". Astronomy & Astrophysics. 535: A55–A66. arXiv:1107.1748. Bibcode:2011A&A...535A..55D. doi:10.1051/0004-6361/201117148. S2CID 119192207.
  5. 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.
  6. Soto, M. G.; Jenkins, J. S. (2018). "Spectroscopic Parameters and atmosphEric ChemIstriEs of Stars (SPECIES). I. Code description and dwarf stars catalogue". Astronomy and Astrophysics. 615: A76. arXiv:1801.09698. Bibcode:2018A&A...615A..76S. doi:10.1051/0004-6361/201731533. S2CID 119107228.
  7. "HD 137388". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-12-25.
  8. "Approved names (§ New Zealand)". Name Exo Worlds. IAU. Retrieved 19 December 2019.
  9. "HD 137388b". Extrasolar Planet Encyclopaedia. Retrieved 20 September 2015.
  10. Agnew, Matthew T.; et al. (2017). "Stable habitable zones of single Jovian planet systems". Monthly Notices of the Royal Astronomical Society. 471 (4): 4494–4507. arXiv:1706.05805. Bibcode:2017MNRAS.471.4494A. doi:10.1093/mnras/stx1449. S2CID 119227856.
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