2MASS J05325346+8246465

2MASS J05325346+8246465 (abbreviated 2MASS J0532+8246) is possibly the first brown dwarf observed in the galactic halo of the Milky Way, and the first known substellar subdwarf star.^[7][8] It was discovered from Two Micron All-Sky Survey data, and verified by observations at Palomar Observatory and W. M. Keck Observatory.^[8] It has a low metallicity, which indicates it is an old star.^[8]

2MASS J05325346+8246465

2MASS J0532+8246 Credit: SDSS
Observation data Epoch J2000      Equinox J2000
Constellation	Camelopardalis
Right ascension	05h 32m 54.4345s[1]
Declination	+82° 46′ 45.161″[1]
Characteristics
Spectral type	esdL8:[2]
Astrometry
Radial velocity (Rv)	−172±1[3] km/s
Proper motion (μ)	RA: 2038.794(561) mas/yr[1] Dec.: −1662.958(484) mas/yr[1]
Parallax (π)	40.7097±0.4597 mas[1]
Distance	80.1 ± 0.9 ly (24.6 ± 0.3 pc)
Details
Mass	0.077–0.085[4] M☉
Temperature	1600[5] K
Metallicity [Fe/H]	−1.6[5] dex
Rotational velocity (v sin i)	65 ±15[3] km/s
Age	~10[5] Gyr
Other designations
2MASS J05325346+8246465,[6] 2MASS 0532+8246
Database references
SIMBAD	data

The mass and temperature of 2MASS 0532+8246 makes it a rare object in stellar-substellar gap between conventional stars and brown dwarfs.^[9] It produces roughly half of its luminosity from hydrogen fusion.^[5] Such "gap" objects, covering a narrow range of masses but a wide range of temperatures, and powered by unsteady hydrogen fusion, are exotic but expected to be more common among low-metallicity objects like 2MASS J05325346+8246465.^[10]

In 2008 it was discovered that this object is on a retrograde galactic orbit that is both eccentric and extends well away from the plane, making this object a member of the galactic halo.^[11] In 2024 this object was identified as a possible member of the Thamnos populations, together with the T subdwarf CWISE J113010.07+313944.7.^[2] Thamnos has two substructures called Thamnos 1 and Thamnos 2, both were identified in 2019 from Gaia data.^[12] Thamnos is likely the remnant of a dwarf galaxy that was accreted into the Milky Way and consists of metal-poor stars that formed between 8 and 12.89 billion years ago.^[13]