# WISE 1828+2650

WISE 1828+2650 (full designation WISEPA J182831.08+265037.8) is a possibly binary brown dwarf or rogue planet of spectral class >Y2, located in the constellation Lyra at approximately 32.5 light-years from Earth. It is the "archetypal member" of the Y spectral class.

## History of observations
### Discovery

WISE 1828+2650 was discovered in 2011 from data collected by NASA's 40 cm (16 in) Wide-field Infrared Survey Explorer (WISE) space telescope at infrared wavelength. WISE 1828+2650 has two discovery papers: Kirkpatrick et al. (2011) and Cushing et al. (2011), however, basically with the same authors and published nearly simultaneously.
* Kirkpatrick et al. presented discovery of 98 new found by WISE brown dwarf systems with components of spectral types M, L, T and Y, among which also was WISE 1828+2650 – coolest of them.
* Cushing et al. presented discovery of seven brown dwarfs – one of T9.5 type, and six of Y-type – first members of the Y spectral class, ever discovered and spectroscopically confirmed, including "archetypal member" of the Y spectral class – WISE 1828+2650. These seven objects are also the faintest seven of 98 brown dwarfs, presented in Kirkpatrick et al. (2011).

## Distance

Currently the most accurate distance estimate of WISE 1828+2650 is a trigonometric parallax, published in 2021 by Kirkpatrick et al.: 100.3±2.0 mas, corresponding to a distance of 10.0±0.2 pc, or 32.5±0.6 ly.

## Proper motion

WISE 1828+2650 has a proper motion of 1,030.5±1.1 milliarcseconds per year.

## Physical properties

Until the discovery of WISE 0855−0714 in 2014, WISE 1828+2650 was considered as the coldest currently known brown dwarf or the first example of free-floating planet (it is not currently known if it is a brown dwarf or a free-floating planet). It has a temperature in the range 250–400 K (−23–127 °C; −10–260 °F) and was initially estimated below 300 K, or about 27 °C (81 °F). It has been assigned the latest known spectral class (>Y2, initially estimated as >Y0).
The mass of WISE 1828+2650 is in the range 0.5–20 M$_{Jup}$ for ages of 0.1–10 Gyr. The high tangential velocity of WISE 1828+2650, characteristic of an old disk population, indicates a possible age of WISE 1828+2650 in the range 2–4 Gyr, leading to a mass estimate of about 3–6 M$_{Jup}$. This suggests that WISE 1828+2650 may be a free-floating planet rather than a brown dwarf, since it is below the lower mass limit for deuterium fusion (~13 M$_{Jup}$).
WISE 1828+2650 is similar in appearance to the other Y-type object WD 0806-661 B. WD 0806-661 B could have formed as a planet close to its primary, WD 0806-661 A, and later, when the primary became a white dwarf and lost most of its mass, have migrated into a larger orbit of 2500 AU, and similarity between WD 0806-661 B and WISE 1828+2650 may indicate that WISE 1828+2650 had formed in the same way.
JWST observation with MIRI detected water vapor (H$_2$O), methane (CH$_4$) and ammonia (NH$_3$) in the atmosphere of WISE 1828+2650. The work detected a low amount of ammonia containing the $^{15}$N isotope when compared to ammonia containing the $^{14}$N isotope. The $^{14}$NH$_3$-to-$^{15}$NH$_3$ ratio was measured as 670. This amount of $^{15}$NH$_3$ is lower than in any Solar System body and it is an indication that WISE 1828+2650 has formed like a star and not like a planet. Thus, this provides evidence that the object is a (sub-)brown dwarf and not a free-floating planet. Another team used the NIRSpec instrument on JWST and detected water vapor, methane, ammonia, carbon monoxide ($^{12}$CO), carbon dioxide (CO$_2$) and hydrogen sulfide (H$_2$S). These molecules are the major carbon, nitrogen, oxygen, and sulfur bearing species in the atmosphere of WISE 1828+2650. The carbon-to-oxygen ratio (C/O ratio) is with 0.45±0.01 close to the solar ratio. The abundance of carbon, oxygen and sulfur is higher than the sun, but the abundance of nitrogen is likely similar to the sun.
Elemental Abundances of WISE 1828+2650 :
| Normalized element abundance | Abundance ([M/H]=0 is solar) |
| [C/H] | +0.24+0.01 −0.02 |
| [O/H] | ≥ +0.34+0.01 −0.02 |
| [N/H] | > −0.31±0.02, might be +0.04 |
| [S/H] | +0.14±0.03 |

### Possible binarity

Comparison between WISE 1828+2650 and WD 0806-661 B may suggest that WISE 1828+2650 is a system of two equal-mass objects. Observations with Hubble Space Telescope (HST) and Keck-II LGS-AO system had not revealed binarity, suggesting that if any such companion exists, it would have an orbit less than 0.5 AU, and no direct evidence for binarity yet exists. However, the spectrum of the system best fits a pair of brown dwarfs, each with an effective temperature of about 325 K and a mass of about 5 M$_J$.
JWST NIRCam imaging observations did not find a companion at a separation larger than 0.5 astronomical units. NIRSpec low resolution prism observations cannot be explained with existing Sonora Bobcat models of planetary objects, neither single nor multiple. The binary model fails to provide an improved fit for the existing photometric data. A newer analysis of the NIRSpec data compared radius determined with atmospheric retrieval framework CHIMERA and evolutionary model Sonora Bobcat. The CHIMERA radius for a single object (1.23±0.01 R$_J$) compared with predicted radius from Sonora Bobcat (10 Gyrs, 33 M$_J$,0.87 R$_J$) is too large for its age, which might be an indication that WISE 1828+2650 is an equal mass binary with both objects having a radius of 0.87 R$_J$. The estimated semi-major axis of this binary is 0.0098+0.002 −0.006 astronomical units or 20+4 −12 R$_J$. Sonora Bobcat however predicts a lower age (1.4 Gyrs) and mass (9.982 M$_J$) when using the temperature and gravity from Sonora Elf Owl atmospheric model grid. Future observations could look for radial velocity variations to confirm the binary.