2MASS J05325346+8246465
Star in the constellation Camelopardalis
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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.[8][9] It was discovered from Two Micron All-Sky Survey data, and verified by observations at Palomar Observatory and W. M. Keck Observatory.[9] It has a low metallicity, which indicates it is an old star.[9]
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Camelopardalis[1] |
| Right ascension | 05h 32m 54.4345s[2] |
| Declination | +82° 46′ 45.161″[2] |
| Characteristics | |
| Spectral type | esdL8:[3] |
| Astrometry | |
| Radial velocity (Rv) | −172±1[4] km/s |
| Proper motion (μ) | RA: 2038.794(561) mas/yr[2] Dec.: −1662.958(484) mas/yr[2] |
| Parallax (π) | 40.7097±0.4597 mas[2] |
| Distance | 80.1 ± 0.9 ly (24.6 ± 0.3 pc) |
| Details | |
| Mass | 0.077–0.085[5] M☉ |
| Temperature | 1600[6] K |
| Metallicity [Fe/H] | −1.6[6] dex |
| Rotational velocity (v sin i) | 65 ±15[4] km/s |
| Age | ~10[6] Gyr |
| Other designations | |
| 2MASS J05325346+8246465,[7] 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.[10] It produces roughly half of its luminosity from hydrogen fusion.[6] 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.[11]
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.[12] In 2024 this object was identified as a possible member of the Thamnos populations, together with the T subdwarf CWISE J113010.07+313944.7.[3] Thamnos has two substructures called Thamnos 1 and Thamnos 2, both were identified in 2019 from Gaia data.[13] 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.[14]