| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hercules |
| Right ascension | 16h 17m 43.2055s[1] |
| Declination | +26° 18′ 15.053″[1] |
| Apparent magnitude (V) | 12.36[2] |
| Characteristics | |
| Spectral type | M |
| Variable type | eclipsing binary,flare star |
| Astrometry | |
| Radial velocity (Rv) | −17.015499±0.008277[3] km/s |
| Proper motion (μ) | RA: −29.265±0.021mas/yr[1] Dec.: 6.860±0.028mas/yr[1] |
| Parallax (π) | 31.7652±0.0259 mas[1] |
| Distance | 102.68 ± 0.08 ly (31.48 ± 0.03 pc) |
| Orbit[4] | |
| Companion | TOI-2119 b |
| Period (P) | 7.2008569±0.0000003 d |
| Semi-major axis (a) | 26.7±0.1 R★ |
| Eccentricity (e) | 0.3355±0.0002 |
| Inclination (i) | 88.47±0.02° |
| Argument of periastron (ω) (secondary) | −0.94±0.09° |
| Semi-amplitude (K1) (primary) | 10.5841+7.7 −8.3 km/s |
| Details[5] | |
| TOI-2119 | |
| Mass | 0.525+0.020 −0.021 M☉ |
| Radius | 0.500±0.015 R☉ |
| Luminosity | 0.0397+0.0013 −0.0012 L☉ |
| Surface gravity (log g) | 4.763±0.018 cgs |
| Temperature | 3621+48 −46 K |
| Metallicity[Fe/H] | +0.055+0.084 −0.077 dex |
| Rotation | 13.11±1.41 d |
| Rotational velocity (v sin i) | 1.61±0.1[4] km/s |
| Age | 1.17±1.15 Gyr |
| TOI-2119 b | |
| Mass | 64.4+2.3 −2.2 MJup |
| Radius | 1.08±0.03 RJup |
| Surface gravity (log g) | 5.132+0.028 −0.020 cgs |
| Temperature | 2030±84 K |
| Other designations | |
| Gaia DR2 1303675097215915264,Gaia DR3 1303675097215915264,TOI-2119,TIC 236387002,GSC 02050-00184,2MASS J16174320+2618151,StM 274,AP J16174320+2618151,1RXS J161742.1+261820,UCAC-2 41034926,UCAC-4 582-052494[6] | |
| b: TOI-2119.01 | |
| Database references | |
| SIMBAD | data |
TOI-2119 is abinary star system composed of aM-type main sequence star and abrown dwarf, discovered by theTransiting Exoplanet Survey Satellite (TESS) in 2020 and announced in 2022.[7][5] It became the first example of a brown dwarf orbiting an M-dwarf to have theobliquity of the system measured using theRossiter–McLaughlin effect.[4]
The system is thought to be afield star, not belonging to any identifiedstellar association ormoving group.[5]
Theeclipsing binary nature of the system was discovered in theTESS mission data of data sectors 24 and 25, recorded from April through June 2020. In addition to a transit signal with ~7.2-day period of transit depthδ =0.04966±0.00030,[5] the observed light curve also exhibitedstellar flares and a ~13.1-day period brightness modulation which was identified with therotation period of the star. In addition to the primary eclipse, where the brown dwarf passes in front of the primary star, a secondary eclipse with the brown dwarf passing behind is also visible with transit depthδ =1053±88 ppm, which allowed for precise measurement of the orbital eccentricity as well as characterization of the brown dwarf's temperature by determination of its brightness relative to the primary.[7][5]
To establish the alignment between the spin of the primary star and the brown dwarf's orbit, subsequent spectroscopic observations were performed using the NEID spectrograph at theWIYN Observatory during two transits on 10 May and 15 June 2023. The obtained spectroscopic data allowed for the characterization ofRossiter–McLaughlin effect. In addition, further observations by TESS in years 2022 and 2024 as well as ground observations were used to further refine the orbital solution.[4]
The system is composed of a primary red dwarf and with a companion brown dwarf in a close, eccentric orbit. This configuration makes the system interesting for investigation oftidal interaction models. The expectedtidal circularization andinspiral time for the system, depending on the choice of the values for thetidal quality factor, are expected to be on the order of ~100 Gyr,[7][5] much longer than the age of the system, implying that the system's primordial orbital configuration is largely preserved. By contrast, brown dwarfs in similar close-in orbits around larger, hotter stars are known to circularize soon after formation,[7] making them unsuitable for studying the formation conditions.
Spectroscopic measurements of theRossiter–McLaughlin effect during the transit have allowed also for the measurement of the system's spin-orbitobliquity, resulting in a value of projected obliquityλ =−0.8°±1.1°, which together with measurements of the inclination of the star's spin axisi★ =72.9°+5.7°
−5.4° allowed for determination of three-dimensional obliquity ofψ =15.7°+5.4°
−5.6°.[4]
The primary star is a young,earlyM dwarf of roughly halfsolar mass. It exhibitsflaring, with roughly two dozen flares of >0.5% over the baseline brightness detected over the initial 60-day observation window byTESS,[5] implying moderatemagnetic activity which explains UV excess detected in thespectrum.[5]
The secondary companion is abrown dwarf with a mass of64.4 MJ[5] and a radius of1.08 RJ.[5] Theeffective temperature of the brown dwarf can be determined from the secondary transit depth to be2030±84 K.[5] The temperature is consistent withspectral type L,[7] however as of 2024[update] the actual spectrum of the brown dwarf has not been resolved yet. This also means that it is not yet possible to determine whether the brown dwarf is metal-rich with no clouds, or cloudy with close to solarmetallicity, same as the primary star.[5]
