LP 944-20 is a dim

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

spectral class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

M9 located 21

light-years A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astro ...

from the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

in the constellation of

Fornax Fornax () is a constellation in the southern celestial hemisphere, partly ringed by the celestial river Eridanus (constellation), Eridanus. Its name is Latin for furnace. It was named by French astronomer Nicolas Louis de Lacaille in 1756. Forna ...

. With a visual

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of 18.69, it has one of the dimmest visual magnitudes listed on the RECONS page. It is one of the brightest brown dwarfs, if not the brightest at J_MKO=.

Discovery

LP 944-20 was discovered in the Luyten-Palomar Survey. It appears as a star with R=17.5 mag with a proper motion of 334 mas/yr in a catalog from 1979. It was however first published in 1975 by Luyten & Kowal. It was re-discovered in the APM survey, a

quasar A quasar ( ) is an extremely Luminosity, luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...

survey, in which the red color was noticed. The first

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

was published in 1997 by Kirkpatrick,

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Irwin Irwin may refer to: Places ;United States * Irwin, California * Irwin, Idaho * Irwin, Illinois * Irwin, Iowa * Irwin, Nebraska * Irwin, Ohio * Irwin, Pennsylvania * Irwin, South Carolina * Irwin County, Georgia * Irwin Township, Venango Co ...

. A spectral type of M9 or later was assigned in this work and a distance of around 5 parsec was established thanks to the parallax being measured. In 1998 Tinney discovered that this M-dwarf shows the 6708 Å Lithium absorption line and

H-alpha Hydrogen-alpha, typically shortened to H-alpha or Hα, is a deep-red visible spectral line of the hydrogen atom with a wavelength of 656.28 nm in air and 656.46 nm in vacuum. It is the first spectral line in the Balmer series and is em ...

emission line, which helped to constrain the age to around 500 million years and established it as a brown dwarf with a mass of around 60 .

Physical characteristics

Short after LP 944-20 was established as a brown dwarf, the fast rotation was detected in 1998. Later a work in 1999 claimed to have detected variability in LP 944-20. A search for dust around LP 944-20 has shown that it has no disk. Due to short rotational period, this young brown dwarf is displaying strong and frequent X-ray flares, and possessing a strong magnetic field reaching 135 G at the

photosphere The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...

level. On 15 December 1999, an

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

flare A flare, also sometimes called a fusée, fusee, or bengala, bengalo in several European countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illuminatio ...

was detected. On 27 July 2000, radio emission (in flare and quiescence) was detected from this brown dwarf by a team of students at the

Very Large Array The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory in the southwestern United States built in the 1970s. It lies in central New Mexico on the Plains of San Agustin, between the towns of Magdalena, Ne ...

. Observations published in 2007 showed that the atmosphere of LP 944-20 contains much

lithium Lithium (from , , ) is a chemical element; it has chemical symbol, symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard temperature and pressure, standard conditions, it is the least dense metal and the ...

and that it has dusty

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles, suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

s. A search for planets was carried out in 2006 using the radial velocity method. No planets were found, but variability with an amplitude of 3.5 km/s was detected. This variability is likely due to weather effects and the rotation of the brown dwarf. In 2015 high resolution Doppler images were taken of LP 944-20 and GJ 791.2A. The time series spectra show line profile distortions, which were interpreted as starspots. These starspots were reconstructed and found to be concentrated at high

latitudes In geography, latitude is a geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at the south pole to 90° at the ...

. The modelling produces a better fit of ΔT= between starspots (T_spot=) and

(T_phot=). In a large program in 2016 the spectral type was established to be M9β in the optical and L0β in the infrared. The beta stands for a surface gravity intermediate between normal and low. The mass was calculated to be . Observations with TESS found that LP 944-20 is variable with a period of around 3.8 hours and an

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...

of . This is in agreement with previous estimates of a period of less than 4.5 hours.

References

External links

"The 100 nearest star systems"
'' Research Consortium on Nearby Stars'' {{Stars of Fornax M-type brown dwarfs Fornax J03393521-3525440 X-ray emitting brown dwarfs