:Gliese 229

A substellar companion was discovered in 1994 by Caltech astronomers Kulkarni, Tadashi Nakajima, Keith Matthews, and Rebecca Oppenheimer, and Johns Hopkins scientists Sam Durrance and David Golimowski. It was confirmed in 1995 as Gliese 229B,{{cite web|title=Astronomers Announce First Clear Evidence of a Brown Dwarf|url=http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/48/|publisher=Space Telescope Science Institute news release STScI-1995-48|date=November 29, 1995|access-date=24 September 2013|archive-date=9 July 2008|archive-url=https://web.archive.org/web/20080709002411/http://hubblesite.org/newscenter/newsdesk/archive/releases/1995/48/|url-status=live}} It was one of the first brown dwarfs discovered. Although too small to sustain hydrogen-burning nuclear fusion as in a main sequence star, with a mass of around 40 to 60 times that of Jupiter (0.06 solar masses), it is still too massive to be a planet. As a brown dwarf, its core temperature is high enough to initiate the fusion of deuterium with a proton to form helium-3, but it is thought that it used up all its deuterium fuel long ago.{{cite book|title=The New Solar System|publisher=Cambridge University Press|author=J. Kelly Beatty|author2=Carolyn Collins Petersen |author3=Andrew Chaikin |date=1999}} This object has a surface temperature of 950 K.

File:GL229LightCurve.png for Gliese 229 showing a small flare, adapted from Byrne et al. (1985)]]

Gliese 229B is the prototype of the T-dwarfs, due to the detection of methane in its spectrum. It also shows other molecules in its atmosphere, namely water vapor, carbon monoxide and ammonia. Atomic absorption lines of caesium, sodium and potassium are also detected.

Gliese 229 B was later found to be a binary brown dwarf. Since 2021 it was suggested to be an unresolved binary, given the inconsistency between the object's measured mass and luminosity. Further evidence that Gliese 229B is an equal-mass binary comes from high-resolution spectroscopy from the Subaru Telescope. Gliese 229 B was then finally resolved in 2024 with VLT/GRAVITY and VLT/CRIRES+. The components are called Gliese 229 Ba and Gliese 229 Bb. The pair is a tight orbit with an orbital period of 12.1 days and a semi-major axis of 0.042 astronomical units (about 16 Earth-Moon distances). The changes in radial velocity extracted from CRIRES+ helped to resolve the orbit of Gliese 229B. The binary has an inclination of 31.4 ±0.3° and an eccentricity of 0.234 ±0.004. The inclination of the binary is misaligned by {{Val|37|7|10}}° in respect to the orbit of Gliese 229B around Gliese 229A. Additional radial velocity changes between two epochs were detected in Gliese 229B with Keck NIRSPEC. This team independently discovered the binarity of Gliese 229B.

The brown dwarf pair was observed with JWST MIRI low resolution spectroscopy. Previous works showed a difference in abundances between host star and companion in Gliese 229 from near-infrared spectra. This new study using mid-infrared data showed that the pair has abundances consistent with the host star. The metallicities were measured to be C/O = 0.65 ±0.05 and [M/H]={{val|0.00|0.04|0.03}} and are equal for each brown dwarf in the pair. The host star has C/O = 0.68 ± 0.12 and [M/H] = −0.02 ± 0.06.

In March 2014, a super-Neptune mass planet candidate was announced in a much closer-in orbit around GJ 229. Given the proximity of the Gliese 229 system to the Sun, the orbit of GJ 229 Ab might be fully characterized by the Gaia space-astrometry mission or via direct imaging. In 2020, a super-Earth mass planet was discovered around GJ 229. GJ 229 Ac orbits the star closer in than GJ 229 Ab, located towards the outer edge but still well inside the star's habitable zone and in that sense similar to Mars in our own Solar System. While considering GJ 229 Ab unconfirmed, the study estimated a significantly lower minimum mass for it.

However, a more recent study found that when stellar activity was taken in account, the radial velocity signals corresponding to the planets' orbital periods disappeared. Therefore, intrinsic activity of the host star or errors in the previous observations are the cause of the radial velocity variations, instead of planets, which mean Gliese 229 Ab and Gliese 229 Ac likely do not exist.

• Epsilon Indi

{{reflist|group=nb|refs=

{{refn|Using the absolute visual magnitude of Gliese 229 A $\backslash scriptstyle\; M\_\{V\_\{\backslash ast\}\}=9.33$ and the absolute visual magnitude of the Sun $\backslash scriptstyle\; M\_\{V\_\{\backslash odot\}\}=4.83$, the visual luminosity can be calculated by $\backslash scriptstyle\; \backslash frac\{L\_\{V\_\{\backslash ast\}\}\}\{L\_\{V\_\{\backslash odot\}\}\}=10^\{0.4\backslash left(M\_\{V\_\{\backslash odot\}\}\; -\; M\_\{V\_\{\backslash ast\}\}\backslash right)\}$|group="nb"|name=luminosity_visual}}

}}

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{{Commons category|Gliese 229}}

• [https://web.archive.org/web/20041031004701/http://starchild.gsfc.nasa.gov/docs/StarChild/shadow/questions/brown_dwarf.html Brown dwarfs (NASA)]
• [https://www.caltech.edu/about/news/its-twins-mystery-of-famed-brown-dwarf-solved It's Twins! Mystery of Famed Brown Dwarf Solved] press release by Caltech

{{Nearest systems|3}}

{{Stars of Lepus}}

{{DEFAULTSORT:Gliese 229}}

Category:Binary stars

Category:Flare stars

0229

Category:Lepus (constellation)

Category:M-type main-sequence stars

Category:T-type brown dwarfs

042581

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BD-21 1377

029295

124279525