HIP 12961

HIP 12961 is a star with an exoplanetary companion in the equatorial constellation of Eridanus. It is too faint to be visible to the naked eye, with an apparent visual magnitude of 10.24.^[2] The distance to this system can be estimated from its parallax measurements, which yield a separation of 76.4 light-years from the Sun. It is receding with a radial velocity of +33 km/s^[5] and has a high proper motion, traversing the celestial sphere at an angular rate of 0.300″ yr⁻¹.^[2]

HIP 12961 / Koeia

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Eridanus
Right ascension	02h 46m 42.8869s[1]
Declination	−23° 05′ 11.802″[1]
Apparent magnitude (V)	10.24[2]
Characteristics
Spectral type	K5V[3] or M0[4]
Apparent magnitude (B)	11.20[2]
Apparent magnitude (J)	7.56[2]
Apparent magnitude (H)	6.93[2]
Apparent magnitude (K)	6.74[2]
B−V color index	1.6
Astrometry
Radial velocity (Rv)	+32.865±0.001[5] km/s
Proper motion (μ)	RA: 294.717(11) mas/yr[1] Dec.: 140.966(15) mas/yr[1]
Parallax (π)	42.6929 ± 0.0141 mas[1]
Distance	76.40 ± 0.03 ly (23.423 ± 0.008 pc)
Absolute magnitude (MV)	8.50±0.09[4]
Details
Mass	0.64 M☉[6] 0.65±0.07[4] M☉
Radius	0.63 R☉[6] 0.61±0.04[4] R☉
Luminosity	0.095±0.018[4] L☉
Surface gravity (log g)	4.65±0.09[7] cgs
Temperature	3,901±175 K[7]4,092±93[4] K
Metallicity [Fe/H]	+0.10±0.06 dex[6] −0.14 dex[7]0.01±0.17[8] dex
Rotational velocity (v sin i)	1.5[6] km/s
Other designations
Koeia, CD−23 1056, HIP 12961, SAO 168043, PPM 245393, LTT 1349, NLTT 8966, TYC 6434-00494-1, 2MASS J02464286-2305119[9]
Database references
SIMBAD	data
Exoplanet Archive	data

This was classified as a cool red dwarf star of stellar classification M0 in 1980,^[4] while C. B. Stephenson graded it as class K5V in 1986.^[3] The absolute magnitude and color index of this star is a closer match to the former. It shows a high chromospheric activity level^[4] and is one of the largest and brightest M class red dwarf stars known, with 64% of the mass and 63% of the radius of the Sun.^[6] The star is radiating 10% of the luminosity of the Sun from its photosphere at an effective temperature of 4,092 K.^[4]

HIP 12961 is named Koeia. The name was selected in the NameExoWorlds campaign by Puerto Rico, during the 100th anniversary of the IAU. Koeia was the word for star in the language of the Taíno Indigenous People of the Caribbean.^[10][11]

Planetary system

HIP 12961 b is an extrasolar planet that was announced in a press release in October 2009. This planet has at least half the mass of Jupiter and takes over eight weeks to orbit the host star at a separation of 0.25 AU and an eccentricity (ovalness) of 0.17.^[12] The planet is named Aumatex. Aumatex was the god of wind in the mythology of the Taíno Indigenous People of the Caribbean.^[10] The names were chosen by the Society of Women in Space Exploration- UPR-Humacao Chapter.^[13]

The HIP 12961 planetary system^[12]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b / Aumatex	≥0.35 MJ	0.25	57.435 ± 0.042	0.166 ± 0.034	—	—

References

1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
2. Winters, Jennifer G.; et al. (2015). "The Solar Neighborhood. XXXV. Distances to 1404 M Dwarf Systems within 25 Pc in the Southern Sky". The Astronomical Journal. 149 (1): 5. arXiv:1401.0722. Bibcode:2015AJ....149....5W. doi:10.1088/0004-6256/149/1/5. S2CID 16953825.
3. Stephenson, C. B. (July 1986). "Dwarf K and M stars of high proper motion found in a hemispheric survey". The Astronomical Journal. 92: 139–165. Bibcode:1986AJ.....92..139S. doi:10.1086/114146.
4. Gaidos, E.; et al. (September 2014). "Trumpeting M dwarfs with CONCH-SHELL: a catalogue of nearby cool host-stars for habitable exoplanets and life". Monthly Notices of the Royal Astronomical Society. 443 (3): 2561–2578. arXiv:1406.7353. Bibcode:2014MNRAS.443.2561G. doi:10.1093/mnras/stu1313. S2CID 119234492.
5. Soubiran, C.; et al. (2018). "Gaia Data Release 2. The catalogue of radial velocity standard stars". Astronomy and Astrophysics. 616: A7. arXiv:1804.09370. Bibcode:2018A&A...616A...7S. doi:10.1051/0004-6361/201832795. S2CID 52952408.
6. Lindgren, Sara; Heiter, Ulrike (2017). "Metallicity determination of M dwarfs. Expanded parameter range in metallicity and effective temperature". Astronomy and Astrophysics. 604: A97. arXiv:1705.08785. Bibcode:2017A&A...604A..97L. doi:10.1051/0004-6361/201730715. S2CID 119216828.
7. Stassun, Keivan G.; et al. (2016). "Accurate Empirical Radii and Masses of Planets and Their Host Stars with Gaia Parallaxes". The Astronomical Journal. 153 (3): 136. arXiv:1609.04389. Bibcode:2017AJ....153..136S. doi:10.3847/1538-3881/aa5df3. S2CID 119219062.
8. Rojas-Ayala, Bárbara; et al. (April 2012). "Metallicity and Temperature Indicators in M Dwarf K-band Spectra: Testing New and Updated Calibrations with Observations of 133 Solar Neighborhood M Dwarfs". The Astrophysical Journal. 748 (2): 93. arXiv:1112.4567. Bibcode:2012ApJ...748...93R. doi:10.1088/0004-637X/748/2/93. S2CID 41902340.
9. "CD-23 1056". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-11-06.
10. "Approved names". NameExoworlds. Retrieved 2020-01-02.
11. "International Astronomical Union | IAU". www.iau.org. Retrieved 2020-01-02.
12. Forveille, Thierry; et al. (February 2011). "The HARPS search for southern extra-solar planets: XXVIII. Two giant planets around M0 dwarfs". Astronomy & Astrophysics. 526: A141. arXiv:1012.1168. Bibcode:2011A&A...526A.141F. doi:10.1051/0004-6361/201016034. ISSN 0004-6361.
13. "Proposers". IAU100 NameExoWorlds. International Astronomical Union. Retrieved 6 May 2022.