SDSS 1624+00 (also known as SDSSp J162414.371+002915.6) is the first

T dwarf An object with the spectral type T (also called T dwarf or methane brown dwarf) is either a brown dwarf or young free-floating planetary-mass object. A directly imaged exoplanet with a young age can also be a T-dwarf. T dwarfs are colder than L ...

discovered in the field, meaning it does free-float in space and does not belong to a group of stars. The object was discovered after Gliese 229B and at around the same time Gliese 570D was discovered. SDSS 1624+00 was discovered in 1999 with preliminary data of the

Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...

. It was selected because of its extreme red color (i-z=3.77 ±0.21 mag). Optical spectroscopy was obtained with the Apache Point 3.5 m telescope and near-infrared photometry and spectroscopy with the United Kingdom Infrared Telescope. The spectrum showed absorption due to

water vapor Water vapor, water vapour, or aqueous vapor is the gaseous phase of Properties of water, water. It is one Phase (matter), state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from th ...

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

and

caesium Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has Symbol (chemistry), symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only f ...

and the spectrum was similar to Gliese 229B, but with SDSS 1624+00 showing a stronger

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

line. It is 1.2 mag fainter than Gliese 229B, which helped to constrain the distance to around 10

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

. A red spectrum was obtained with the

Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and, when c ...

. The researchers found that SDSS 1624+00 is likely warmer than Gliese 229B, due to stronger absorption by alkali metals (caesium, potassium and

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

). Later it was discovered that Gliese 229B is a binary, which can cause differences in the spectrum. SDSS 1624+00 was assigned a spectral type of T6 by two teams at the same time. SDSS 1624+00 was one of the few T-dwarfs observed with JWST NIRSpec and

MIRI Miri () is a coastal city in north-eastern Sarawak, Malaysia, located near the border of Brunei, on the island of Borneo. The city covers an area of , located northeast of Kuching and southwest of Kota Kinabalu. Miri is the second largest ...

spectroscopy, which revealed additional molecules in its atmosphere, namely

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

and

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

Potential variability

Additional near-infrared spectra were obtained with the

Subaru Telescope is the telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii. It is named after the open star cluster known in English as the Pleiades. It had the largest monolithic primary mirror in the ...

. The multiple spectra taken over a period of 80 minutes showed possible variability in the water vapor absorption. Later observations did not find water vapor variability in spectra with the

Very Large Telescope The Very Large Telescope (VLT) is an astronomical facility operated since 1998 by the European Southern Observatory, located on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each equipped with ...

. Potential strong water vapor variability was also found with Hubble WFC3. Observations on

Kitt Peak Kitt Peak () is a mountain in the U.S. state of Arizona, and at is the highest point in the Quinlan Mountains. It is the location of the Kitt Peak National Observatory. The radio telescope at the observatory is one of ten dishes comprising the ...

2.1 m telescope also found low significance evidence for variability of this T-dwarf. Analysis of archived WFC3 data later found it not to be variable.

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