Gliese 900

Gliese 900 (GJ 900, BD+00 5017) is a triple star system, located 68 light-years from Earth in the constellation Pisces. It is made up of three main sequence stars: one is a K-type star, the two others are M-dwarf stars. The two M-dwarfs form a binary system with a period of 36 years, and this system has a period of 80 years around the primary component. With an apparent magnitude of 9.546, Gliese 900 is not visible to the naked eye. A widely separated planet has been detected around the system.^[8]

Gliese 900

Gliese 900 imaged by WISE, with the planetary-mass companion circled
Observation data Epoch J2000      Equinox J2000
Constellation	Pisces[1]
Right ascension	23h 35m 00.27674s[2]
Declination	+01° 36′ 19.4347″[2]
Apparent magnitude (V)	9.546[2]
Characteristics
A
Evolutionary stage	Main sequence
Spectral type	K5-7[3]
B−V color index	1.35[4]
B
Evolutionary stage	Main sequence
Spectral type	M3-4[3]
C
Evolutionary stage	Main sequence
Spectral type	M5-6[3]
Astrometry
Radial velocity (Rv)	−10.44±0.44[5] km/s
Proper motion (μ)	RA: 340.029 mas/yr[5] Dec.: 28.456 mas/yr[5]
Parallax (π)	47.9641±0.0236 mas[5]
Distance	68.00 ± 0.03 ly (20.85 ± 0.01 pc)
Absolute magnitude (MV)	7.95[a]
Details
A
Mass	0.64 – 0.67[3] M☉
Radius	0.716±0.021[6] R☉
Luminosity	0.12±0.005[5] L☉
Temperature	4,079±180[3] K
Metallicity [Fe/H]	0.02[7] dex
Rotation	11.9[8] days
Age	200±50[8] Myr
B
Mass	0.28 – 0.34[3] M☉
C
Mass	0.16 – 0.24[3] M☉
Orbit
Primary	A
Companion	BC
Period (P)	≈80[3] yr
Orbit[7]
Primary	B
Companion	C
Period (P)	36 yr
Semi-major axis (a)	444 mas (9.217 AU)[b]
Eccentricity (e)	0.136
Inclination (i)	82.21°
Argument of periastron (ω) (secondary)	109.8°
Position (relative to A)[3]
Epoch of observation	December 2006
Angular distance	751 (A–B) 708 (A–C) 51 (B–C) mas
Position angle	342.5 (A–B) 344.7 (A–C) 130.3 (B–C)°
Other designations
BD+00 5017, GJ 900, HIP 116384, WDS J23350+0136A,BC, G 29-47 / 157-46, LSPM J2235+0136, TIC 422618003, TYC 585-236-1, GSC 00585-00236, 2MASS J23350028+0136193, WISE J233500.50+013619.7
Database references
SIMBAD	data
Exoplanet Archive	data

Stellar system

Location of Gliese 900 (circled)

Gliese 900 is a hierarchical star system, made up of three main sequence stars: The primary component (Gliese 900 A) is a K5-K7 type star, that has 0.64–0.67 times the mass of the Sun,^[3] 0.72 times its radius,^[6] and 12% its luminosity.^[5] A light curve from the Transiting Exoplanet Survey Satellite (TESS) shows that its rotational period is 12 days.^[8] Gliese 900 A has a high level of chromospheric and coronal activity, although its apparent brightness presents little variation.^[9] The other components are red dwarf stars. Gliese 900 B has a spectral type of M3–M4 and a mass between 0.24 and 0.34 solar masses. Gliese 900 C has a spectral type of M5–M6 and a mass between 0.16 and 0.24 solar masses.^[3]

The system is young, about 200 million years old, and is a likely member (99.7% probability) of the nearby moving group Carina-Near.^[10] It is a source of X-ray emission, with an observed flux of 9.13×10² mW M^-2, and is also a source of ultraviolet emission.^[8] The emission of X-rays is typical of young stars, and classifies it as one.^[9] The TESS light curve identifies stellar flares on this star.^[8]

Orbit

Gliese 900 B and C form an inner pair (named Gliese 900 BC) with an orbital period of around 36 years.^[7] Gliese 900 BC and Gliese 900 A orbit the system's center of mass with a period of 80 years.^[3][8] As of November 2004,^[update] B was separated from A by 751 milliarcseconds and C was separated from A by 708 mas. This separation changes over time.^[3] It was identified as a multiple star system in 2002 by Eduardo L. Martín, using adaptive optics-corrected images at the 8.2 m Subaru Telescope. When first observed, the A–B and A–C separations were of 0.51 and 0.76 arcsecs respectively.^[9] A further study by Malogolovets et al. (2007) identified this system as a hierarchical triple.^[3]

Other stars in the system

Malogolovets et al. (2007) reported two other objects in 2MASS images (potentially late red dwarfs) that would be the components D and E and make the system quintuple, being "very likely" to be bound to the system.^[3] However, these faint stars haven't been confirmed as members of the GJ 900 system, and are likely not associated.^[8]

Motion

Gliese 900 is located 68 light-years from Earth, based on parallax measurements by the Gaia spacecraft.^[5] The BP-RP spectra suggest a distance of 67.7 ly.^[5] The space velocity components of this system are U = −28.7, V = −15 and W = 0.2.^[11] Gliese 900 is part of the thin disk population of the Milky Way.^[11][3] It was once classified as part of the IC 2602 supercluster.^[9] A newer analysis using kinematics from the Gaia spacecraft suggest that Gliese 900 has a 99.7% chance of being a member of the Carina-Near moving group and a 0.3% chance of being a field star, i.e. not associated to any star cluster or stellar association.^[8]

Planetary system

A 2024 study led by Austin Rothermich identified CWISE J233531.55+014219.6 (abbreviated to CW2335+0142) as a proper motion companion to Gliese 900, with 99.5% probability.^[8] This object, also called Gliese 900 b or Gliese 900 (ABC)b,^[12][13] is a planetary-mass object that has 10.5 times the mass of Jupiter (0.01 times the mass of the Sun), a spectral type T9^[8] and a temperature of 500 K.^[14] It was found to be at an angular separation of 587" from Gliese 900. At the estimated distance to this system, it translates to a projected separation of 12,000 AU.^[8]

As of 2024^[update], Gliese 900 b has the largest observed separation of any known planet, and assuming a circular orbit, the longest orbital period.^[15][16][c] The orbital period is estimated at 1.27 million years based on the projected separation.^[17] Due to the similar spectral type, orbital separation and age, Gliese 900 b has been compared to COCONUTS-2b by the discovery team.^[8]

Also in 2024, a study using data from Wide-field Infrared Survey Explorer found a red W2-W3 color for Gliese 900 b, which the researchers interpret as a sign of low gravity for T-dwarfs. Low gravity is often seen as an indicator of a young age and a low mass.^[14]

Gliese 900 planetary system^[8]

Companion (in order from star)	Mass	Projected separation (AU)	Orbital period (106 years)	Eccentricity	Inclination	Radius
b	10.5 MJ	12,000	1.27[17]	–	–	1.11 RJ (estimate)[17]

See also

• Circumtriple planet, a category of planets to which Gliese 900 b belongs
• List of exoplanets discovered in 2024 - including Gliese 900 b

Notes

1. Using the apparent magnitude and distance from Earth, Gliese 900's absolute magnitude can be calculated.
   9.546+5−5*log(20.85) = 7.95.
2. Using the angular separation and the parallax (both in milliarcseconds), the physical separation (in AU) can be obtained.
   444/48.17 = 9.217 AU.
3. Out of objects with a planetary mass (<13 M_J). Exoplanet databases list a few brown dwarfs at larger separations.