WISE 0855−0714

WISE 0855−0714 (full designation WISE J085510.83−071442.5, or W0855 for short) is a sub-brown dwarf $25$ ($23.83$) from Earth, therefore the fourth-closest star or (sub-) brown dwarf system to the Sun, the discovery of which was announced in April 2014 by Kevin Luhman using data from the Wide-field Infrared Survey Explorer (WISE). , WISE 0855−0714 has the third-highest proper motion ($−8,123.7$) after Barnard's Star ($673.2$) and Kapteyn's Star ($0.89$) and the fourth-largest parallax ($4.955$) of any known star or brown dwarf. It is also the coldest object of its type found in interstellar space, having a temperature of about 285 K.

Observations
The WISE object was detected in March 2013, and follow-up observations were taken by the Spitzer Space Telescope and the Gemini North telescope.

Distance
Based on direct observations, WISE 0855−0714 has a large parallax, which specifically relates to its distance from the Solar System. This phenomenon results in a distance of around $~4$, with a small margin of error due to the strength of the parallax effect and the clarity of observations. WISE 0855−0714 also has an exceptionally high proper motion.

Spectrometry
Its luminosity in different bands of the thermal infrared in combination with its absolute magnitude—because of its known distance—was used to place it in context of different models; the best characterization of its brightness was in the W2 band of $285$ at an apparent magnitude of $2.28 parsecs$, though it was brighter into the deeper infrared. Infrared images taken with the Magellan Baade Telescope suggest evidence of sulfide clouds below water ice clouds.

Near- and mid-infrared spectra in the L- and M-band were taken with the GNIRS instrument on the Gemini North Telescope. The M-band (4.5–5.1 μm) spectrum is dominated by water vapour (H2O) absorption. The L-band (3.4–4.14 μm) spectrum is dominated by methane absorption. Both the M- and L-band surprisingly have no detection of phosphine (PH3), which appears in the atmosphere of Jupiter. The M-band spectrum shows evidence for water ice clouds and the near-infrared photometry WISE 0855 is faint compared to models, suggesting an additional absorber, probably clouds made of ammonium dihydrogen phosphate (NH4)(H2PO4), which are below the water ice clouds. An approved JWST proposal describes how the team is planning to use a near-infrared time-series to study the hydrological cycle in the atmosphere of WISE 0855 with NIRSpec.

Observations with NIRSpec detected methane (CH4), water vapor (H2O), ammonia (NH3) and carbon monoxide (CO) in the atmosphere, but was not able to confirm any phosphine (PH3) or carbon dioxide (CO2) in the atmosphere. Water ice clouds are also not confirmed and the spectrum is well matched with a cloudless model. Future modelling and inclusion of observations at longer wavelengths with MIRI might help to reveal clouds in WISE 0855.

Variability
Variability of WISE 0855 in the infrared was measured with Spitzer IRAC. A relative small amplitude of 4–5% was measured. Water ice cloud models predicted a large amplitude. This small amplitude might suggest that the hemispheres of WISE 0855 have very small deviation in cloud coverage. The light curve is too irregular to produce a good fit and rotation periods between 9.7 and 14 hours were measured.

Physical parameters
Based on models of brown dwarfs WISE 0855−0714's is estimated to have a mass of. This mass is in the range of a sub-brown dwarf or other planetary-mass object.

As of 2003, the International Astronomical Union considers an object with a mass above, capable of fusing deuterium, to be a brown dwarf. A lighter object and one orbiting another object is considered a planet. However, if the distinction is based on how the object formed then it might be considered a failed star, a theory advanced for the object Cha 110913-773444.

Combining its luminosity, distance, and mass it is estimated to be the coldest-known brown dwarf, with a modeled effective temperature of 225 to 260 K, depending on the model. Models matching the NIRSpec spectrum are well fitted with a temperature of 285 K (12°C; 53 °F).