| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Reticulum |
| Right ascension | 03h 48m 07.721s[1] |
| Declination | –60° 22′ 27.062″[1] |
| Characteristics | |
| Spectral type | T7[2] |
| Apparent magnitude (J) | 15.318 ± 0.050[1] |
| Apparent magnitude (H) | 15.559 ± 0.143[1] |
| Apparent magnitude (K) | 15.602 ± 0.230[1] |
| Astrometry | |
| Radial velocity (Rv) | −14.1 ± 3.7[2] km/s |
| Proper motion (μ) | RA: –279.7 ± 0.6[3]mas/yr Dec.: –768.5 ± 0.7[3]mas/yr |
| Parallax (π) | 120.1±1.8 mas[3] |
| Distance | 27.2 ± 0.4 ly (8.3 ± 0.1 pc) |
| Details[2] | |
| Mass | 0.041+0.021 −0.017 M☉ |
| Radius | 0.093+0.016 −0.010 R☉ |
| Surface gravity (log g) | 5.1 ± 0.3 cgs |
| Temperature | 880 ± 110 K |
| Rotation | 1.080+0.004 −0.005 h |
| Rotational velocity (v sin i) | 103.5 ± 7.4 km/s |
| Age | 3.5+11.5 −2.9 Gyr |
| Other designations | |
| WISE J034807.33-602234.9,WISEA J034807.33-602235.2,WISEP J034807.34-602234.9, UGCS J121951.36+312849.4,TIC 237922091[1] | |
| Database references | |
| SIMBAD | data |
2MASS J03480772−6022270 (abbreviated to2MASS J0348−6022) is abrown dwarf ofspectral class T7, located in the constellationReticulum approximately 27.2light-years from theSun. It was discovered by astronomer Adam Burgasser and collaborators of the 2MASS Wide-Field T Dwarf Search in 2002. With arotation period of 1.08hours, it is the fastest-rotating brown dwarf confirmed as of 2022[update].[4] Therotational velocity at its equator is over 100 km/s (62 mi/s), approaching the predictedrotational speed limit beyond which it would break apart due tocentripetal forces.[5] As a consequence of its rapid rotation, the brown dwarf is slightly flattened at its poles to a similar degree asSaturn, the mostoblateplanet in theSolar System. Its rapid rotation may enable strongauroralradio emissions via charged particle interactions in itsmagnetic field, as observed in other known rapidly-rotating brown dwarfs.[2]
2MASS J0348−6022 was first catalogued as apoint source in June 2003 by theTwo Micron All-Sky Survey (2MASS) organized by theUniversity of Massachusetts Amherstand theInfrared Processing and Analysis Center under theCalifornia Institute of Technology.[6] It was discovered to be abrown dwarf of thespectral class T7 by Adam Burgasser and collaborators of the 2MASS Wide-Field T Dwarf Search, based onspectra in thenear-infrared region of theelectromagnetic spectrum obtained in September 2002 with theVíctor M. Blanco Telescope at theCerro Tololo Inter-American Observatory,Chile. Their discovery and characterization of 2MASS J0348−6022 along with two other T dwarfs located in thesouthern celestial hemisphere was published inThe Astronomical Journal in November 2003.[7]
2MASS J0348−6022 is located in the southern celestial hemisphere in the constellationReticulum.[7] Itsequatorial coordinates based on theJ2000 epoch are:RA03h 48m 07.72s andDec –60° 22′ 27.0″.[1] These coordinates insexagesimal notation are displayed in its identifier 2MASS J03480772−6022270.[6] Thetrigonometric parallax of 2MASS J0348−6022 has been measured to be120.1±1.8milliarcseconds, from 16 observations by theNew Technology Telescope (NTT) collected over 6.4 years.[3] This corresponds to a distance of 8.3 ± 0.1parsecs (27.2 ± 0.4 ly). A previous estimate by Burgasser and collaborators from thespectrophotometric relation of spectral type and near-infraredabsolute magnitude resulted in a value of 9 ± 4parsecs (29 ± 13 ly), based on 2MASSJHK-bandphotometry.[7]
The NTT has also measured the proper motion of 2MASS J0348−6022 in two directions: RA−279.7±0.6 mas/yr and Dec−768.5±0.7 mas/yr, which indicate motion in south-west direction on the sky.[3] Given the distance estimate from trigonometric parallax, the correspondingtangential velocity is32.3±0.5 km/s, consistent with thekinematics of the stars of theGalactic disk.[3][7]
2MASS J0348−6022 is classified as alate T-type brown dwarf with the spectral class T7, distinguished by the presence of strongmethane (CH4) and water (H2O)absorption bands in its near-infrared spectrum betweenwavelengths 1.2 and 2.35 μm.[7] The near-infrared spectrum of 2MASS J0348−6022 also displays a pair of narrowabsorption lines at 1.243 and 1.252 μm, which are attributed to the presence of neutralpotassium (K I) in the brown dwarf's atmosphere. Compared to other T dwarfs, the K I doublet lines in 2MASS J0348−6022's spectrum appear relatively faded due to its late spectral type; K I doublet lines are typically more prominent in the spectra of early- and mid-type T dwarfs as well as late-type L andM dwarfs.[7] Absorption bands ofiron(I) hydride (FeH) have also been found in 2MASS J0348−6022's spectrum between 1.72–1.78 μm.[2]
Like most T dwarfs, the optical and near-infrared color of 2MASS J0348−6022 is very red. The near-infrared 2MASScolor indices areJ–H =−0.24±0.16 andH–K =−0.04±0.28, indicating that the brown dwarf appears brighter in longer (thus redder) wavelengths of light.[7]
The near-infrared spectrum of a brown dwarf can be modelled by aphotosphere primarily defined by two fixed intrinsic properties:effective temperature (Teff) andsurface gravity (log g).[2] In a 2021 study, Megan Tannock and collaborators compared the near-infrared spectrum of 2MASS J0348−6022 to various published photospheric models and derived multiple best-fit solutions for its effective temperature and surface gravity. They took aweighted mean of these best-fit solutions and adopted the following values for these two fundamental properties:Teff =880±110 K and logg =5.1±0.3dex (105.1 times Earth's gravity incentimetre-gram-second units). From photospheric modeling they were also able to determine 2MASS J0348−6022'sradial velocity andprojected rotational velocity, which facilitated the confirmation of the brown dwarf's rapid rotation.[2]
Themass,radius, andage of 2MASS J0348−6022 are estimated by interpolation of brown dwarfevolutionary models based on effective temperature and surface gravity. From their adopted effective temperature and surface gravity values from photospheric modelling, Tannock and collaborators derive a mass of0.041+0.021
−0.017 M☉ (~43MJup), aJupiter-like equatorial radius of0.093+0.016
−0.010 R☉ (69,700 km), and an age of3.5+11.5
−2.9 billion years.[2] The high estimated age of 2MASS J0348−6022 is due to its late T-type spectral class, which is generally expected to describe the later evolutionary stages of brown dwarfs as they cool.[8]
2MASS J0348−6022 is the fastest-rotating brown dwarf confirmed as of 2022[update], with a photometricperiodicity of1.080+0.004
−0.005 hours.[a] It along with L dwarfs2MASS J1219+3128 and2MASS J0407+1546 have had their short rotation periods measured and studied in detail in 2021 by Megan Tannock and collaborators using data from theSpitzer Space Telescope.[5] The double-peakedlight curve of 2MASS J0348−6022 may indicate the presence of two dominant photospheric spots configured on opposite hemispheres of the brown dwarf.[2]
Photometric variability in 2MASS J0348−6022 was first reported in 2008 by Fraser Clarke and collaborators using theNew Technology Telescope's (NTT) near-infraredspectrograph. They reported an upper limitJ-bandamplitude of <1% in a six hour observation period.[10] Likewise, astrophysicist Jacqueline Radigan estimated aJ-band amplitude of <1.1%±0.4% in an independent analysis of 2011–2012 NTT observations published by Paul Wilson and collaborators in 2014, who initially derived a spuriously high amplitude of2.4%±0.5% due tosystematic errors in their measurement.[11][8] Low-amplitude (<2%) variability is common among brown dwarfs of all spectral types, and is presumed to be the result of patchy photospheres with subtle heterogeneities.[11]
Infrared observations by the Spitzer Space Telescope show that 2MASS J0348−6022's brightness appears flat in theInfrared Array Camera's 3.6 μm band and only exhibits discernible variability in the 4.5 μm band, a behavior typical of previously observed T dwarfs. This can be explained by the presence of CH4 in its atmosphere, which is opaque to wavelengths around 3.3 μm.[2]
The spectral lines in 2MASS J0348−6022's spectrum areDoppler-broadened due to the brown dwarf's rapid rotation, consistent with its short photometric periodicity. This rotational broadening can be modelled as a function of the brown dwarf's projected rotational velocity (v sini), which is estimated at 103.5 ± 7.4 km/s (64.3 ± 4.6 mi/s).[2]
The rotational velocity at 2MASS J0348−6022's equator (v) is separately calculated from its radius and rotation period, giving105+18
−12 km/s. While it has the highest reportedv sini value of all knownultra-cool dwarfs, its equatorial rotational velocity only comes second after the slightly larger L8 dwarf 2MASS J1219+3128. The high equatorial rotational velocity of 2MASS J0348−6022 decreases the surface gravity at its equator due tocentrifugal acceleration, though this has a negligible effect on the validity of the nominal surface gravity logg =5.1±0.3 dex inferred from photospheric modelling.[2]
The centrifugal forces exerted by its rapid rotation also cause the brown dwarf to becomeoblate, being slightly flattened at its poles. Tannock and collaborators calculate an oblateness of 0.08; the difference between the brown dwarf's polar and equatorial radii is 8%. For comparison, theSolar System's most oblateplanetSaturn has an oblateness of 0.10.[2] 2MASS J0348−6022 is expected to exhibit significantlinear polarization in its optical and infrared thermal emission due to its oblate, dusty atmosphere induced by its rapid rotation and lower surface gravity.[2][12]
Extrapolations for the breakup periods of typical brown dwarfs older than 1 billion years range tens of minutes depending on mass and radius. The high spin rate and oblateness of 2MASS J0348−6022 places it at about 45% of its rotational stability limit, assuming a smoothly varyingfluid interior. Taking into account of magneticdynamos generated by the brown dwarf'smetallic hydrogen interior, the rotational velocity threshold may be even lower and implies that 2MASS J0348−6022 may be closer to breakup than predicted.[2] As brown dwarfs cool and age, they contract in size and spin faster to conserveangular momentum; theoretically rapid rotators like 2MASS J0348−6022 should eventually approach their rotational stability limit and break apart, but no such phenomena have been observed as of 2021[update].[2] It is possible that some unknown rotational braking mechanism may be preventing brown dwarfs from breaking up as they age.[5]
The rapid rotation of 2MASS J0348−6022 may enhance itsmagnetic field through a dynamo process involvingconvection induced bydifferential rotation in its interior. This in turn enables strongaurorae in the form ofcircularly polarizedradio wave emissions via charged particle interactions in its magnetic field, which are driven by the so-calledelectroncyclotronmaser instability that has been observed in other known rapidly-rotating and radio-emitting brown dwarfs.[13] Theinclination of 2MASS J0348−6022's spin axis to Earth is81°+9°
−27°, derived from itsv sini value. This places it in a nearly equator-on configuration viewed from Earth, which makes it a favorable target for observing these hypothesized auroral radio emissions.[2]
The other two discoveries of rapidly-rotating brown dwarfs, presented in Tannock et al. (2021):[2]
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