WISE 1405+5534

WISEPC J140518.40+553421.4 is a brown dwarf of spectral class Y0, located in constellation Ursa Major at approximately 20.6 light-years from Earth. It is one of the Sun's nearest neighbors.

Discovery

WISE 1405+5534 was discovered in 2011 from data collected by the Wide-field Infrared Survey Explorer in the infrared at a wavelength of 40 cm. WISE 1405+5534 has two discovery papers: Kirkpatrick et al. and Cushing et al. , 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 1405+5534.
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, and WISE 1405+5534. These seven objects are also the faintest seven of 98 brown dwarfs, presented in Kirkpatrick et al. .

Distance

An older distance estimate of WISE 1405+5534 is a trigonometric parallax, measured using Spitzer Space Telescope and published in 2013 by Trent Dupuy and Adam Kraus: 0.129 ± 0.019 arcsec, corresponding to a distance 7.8 pc, or 25.3 ly. Later the parallax was refined to 158.2 mas, showing that it is closer at about 6.3 pc, or 20.6 light years.
WISE 1405+5534 distance estimates

Source	Parallax, mas	Distance, pc	Distance, ly	Ref.
Kirkpatrick et al., Table 6		~ 8.6	~ 28.0
Cushing et al., Table 7		~ 3.8	~ 12.4
Marsh et al.	207 ± 39	4.8	15.8
Marsh et al.	133 ± 81	>3.4	>11.1
Dupuy & Kraus	129 ± 19	7.8	25.3

Non-trigonometric distance estimates are marked in italic. The most precise estimate is marked in bold.

Space motion

WISE 1405+5534 has a large proper motion of about 2281 milliarcseconds per year.
WISE 1405+5534 proper motion estimates

Source	μ, mas/yr	P. A., °	μ_RA, mas/yr	μ_DEC, mas/yr	Ref.
Kirkpatrick et al.	2693	272	-2691 ± 292	95 ± 271
Marsh et al.	2307	275	-2297 ± 96	212 ± 137
Dupuy & Kraus	2281 ± 48	277.3 ± 1.0	−2263 ± 47	288 ± 41

The most accurate estimates are marked in bold.

Physical properties

The object's temperature estimate is 350 K . Its spectrum is similar with spectrum of another Y-dwarf WISE 1738+2732. However, WISE 1405+5534's spectrum has a red shift of H-band flux peak, suggesting that WISE 1405+5534 may be peculiar, therefore it is classified as Y0. One work has shown that models that include optically thin sulfides, KCl and Cr clouds fit the observed photometry of WISE 1405+5534 better. This is however a tentative result. At this low temperature of WISE 1405+5534 water should condense and form clouds. Another team observed WISE 1405+5534 with the Very Large Array to search for radio emission coming from an aurora, but was not able to detect any.

Variability

WISE 1405+5534 was the first Y-dwarf with a detected variability. The discovery was made with the Spitzer Space Telescope. The Y-dwarf was observed in two epochs. The first epoch was a 24-hour-long observation and the second epoch was 149 days later and was also 24 hours long. The first epoch is only variable at 4.5 μm and the second epoch is variable in both 3.6 and 4.5 μm. This means that the variability changes on the timescale of months. The light curve in the second epoch had a semi-amplitude of 3.5% and a rotation period of 8.5 hours. A single bright spot reproduced the observations well. Other models that included clouds and hot spots were not able to reproduce the variability.