GJ 9827

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GJ 9827
Observation data
Epoch J2000      Equinox J2000
Constellation Pisces
Right ascension  23h 27m 04.8377s[1]
Declination −01° 17′ 10.5856″[1]
Apparent magnitude (V) 10.250[2]
Spectral type K6 V[2]
B−V color index +1.30[3]
Radial velocity (Rv)27.00 ± 3.7[4] km/s
Proper motion (μ) RA: 376.019±0.094[1] mas/yr
Dec.: 216.071±0.070[1] mas/yr
Parallax (π)33.6855 ± 0.0611[1] mas
Distance96.8 ± 0.2 ly
(29.69 ± 0.05 pc)
Mass0.667 ± 0.023[2] M
[2] R
[2] L
Surface gravity (log g)4.786+0.074
[2] cgs
Temperature4270 ± 100[2] K
Metallicity [Fe/H]−0.5 ± 0.1[2] dex
Rotational velocity (v sin i)1.3 ± 1.5[2] km/s
Other designations
BD−02° 5958, GJ 9827, HIP 115752[6]
Database references

GJ 9827 is a star in the constellation of Pisces. It is a K-type main-sequence star with an apparent magnitude of 10.250.[2] It is 97 light-years (30 parsecs) away, based on parallax.[1]

It has 3 transiting planets seen by the Kepler space observatory in their K2 survey. As of October 2017, it is the closest star discovered to have transiting exoplanets found by either the Kepler or K2 missions. The planets (b, c, d) have radii of 1.62, 1.27, and 2.09 times that of the Earth, and periods of 1.209, 3.648, and 6.201 days (ratios 1:3:5).[2] Because of its close distance the system is considered an excellent target for studying atmospherics of exoplanets.

In late 2017, the masses of all three planets were determined using the Planet Finder Spectrograph on the Magellan II Telescope. Planet b was found to be very iron-rich, planet c appears to be mainly rocky, and planet d is a typical volatile-rich planet. GJ 9827b is noted as being one of the densest planets yet found, with its mass containing about ≥50% iron.[2]

More precise radial velocity measurements released in late February 2018 revealed that all three planets have a lower density than Earth and have some amount of volatiles in their compositions. GJ 9827b and c are mainly rocky with very thin volatile envelopes, while GJ 9827d is more akin to a Mini-Neptune. With a mass of about 1.5 M, GJ 9827c is one of the least massive planets detected with radial velocity.[7]

The GJ 9827 planetary system[2][7]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 3.74+0.50
c 1.47+0.59
d 2.38+0.71
6.201472 ± 0.000061 87.722+0.077


  1. ^ a b c d e f 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. ^ a b c d e f g h i j k l m Rodriguez, Joseph E; Vanderburg, Andrew; Eastman, Jason D; Mann, Andrew W; Crossfield, Ian J. M; Ciardi, David R; Latham, David W; Quinn, Samuel N (2018). "A System of Three Super Earths Transiting the Late K-Dwarf GJ 9827 at 30 pc". The Astronomical Journal. 155 (2): 72. arXiv:1709.01957. Bibcode:2018AJ....155...72R. doi:10.3847/1538-3881/aaa292.
  3. ^ Mumford, G. S. (1956). "Photoelectric observations of red dwarf stars". Astronomical Journal. 61: 213–218. Bibcode:1956AJ.....61..213M. doi:10.1086/107329.
  4. ^ Kharchenko, N. V.; et al. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776.
  5. ^ Niraula, Prajwal; et al. (2017). "Three Small Super-Earths Transiting the nearby star GJ 9827". The Astronomical Journal. 1709 (6): arXiv:1709.01527. arXiv:1709.01527. Bibcode:2017AJ....154..266N. doi:10.3847/1538-3881/aa957c.
  6. ^ "BD-02 5958". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 8 October 2017.
  7. ^ a b Prieto-Arranz, J.; et al. (2018). "Mass determination of the 1:3:5 near-resonant planets transiting GJ 9827 (K2-135)". Astronomy and Astrophysics. 618. A116. arXiv:1802.09557. Bibcode:2018A&A...618A.116P. doi:10.1051/0004-6361/201832872.

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