WISE J080822.18−644357.3 – a 45 Myr-old accreting M dwarf hosting a primordial disc

Abstract

WISE J080822.18-644357.3 (WISE J0808-6443) was recently identified as a new M dwarf debris disc system and a candidate member of the 45 Myr-old Carina association. Given that the strength of its infrared excess (L IR /L 0.1) appears to be more consistent with a young protoplanetary disc, we present the first optical spectra of the star and reassess its evolutionary and membership status. We find WISE J0808−6443 to be a Li-rich M5 star with strong Hα emission (−125 < EW < −65 Å over 4 epochs) whose strength and broad width are consistent with accretion at a low level (∼10 −10 M yr −1 ) from its disc. The spectral energy distribution of the star is consistent with a primordial disc and is well-fit using a two-temperature blackbody model with T inner 1100 K and T outer 240 K. AllWISE multi-epoch photometry shows the system exhibits significant variability in the 3.4 µm and 4.6 µm bands. We calculate an improved proper motion based on archival astrometry, and combined with a new radial velocity, the kinematics of the star are consistent with membership in Carina at a kinematic distance of 90 ± 9 pc. The spectroscopic and photometric data are consistent with WISE J0808−6443 being a ∼0.1 M Classical T-Tauri star and one of the oldest known accreting M-type stars. These results provide further evidence that the upper limit on the lifetimes of gas-rich discsand hence the timescales to form and evolve protoplanetary systems -around the lowest mass stars may be longer than previously recognised, or some mechanism may be responsible for regenerating short-lived discs at later stages of pre-main sequence evolution.

The Elusive Majority of Young Moving Groups. I. Young Binaries and Lithium-rich Stars in the Solar Neighborhood

“…We find a somewhat later spectral type of K7 from our SOAR spectra. Our lithium measurement (EW ≈ 270 mÅ) is comparable to that of Torres et al (2006) (EW = 330 mÅ) and suggests an age between TWA and AB Dor (e.g., Murphy et al 2018). The velocities of this system are U =-8.8 ± 0.07 km s −1 , V =--21.6 ± 0.18 km s −1 , and W =-2.1 ± 0.05 km s −1 .…”

“…Riedel et al (2014) identify this close binary as a possible member of Carina or Columba. If it is a member of either of these groups and if the strong Hα originates from ongoing accretion, this would be an unusually long disk dissipation timescale possibly similar to the peculiar system found by Murphy et al (2018).…”

The age of the carina young association and potential membership of HD 95086

“…48±0.27 (Gaia Collaboration et al 2018) 100.0 UCAC3 53-40215 5297100607744079872 21.17±0.41 (Schneider et al 2019) 100.0 2MASS J08040534-6316396 5277462269217606400 22.0±0.85 (Schneider et al 2019) 100.0 2MASS J09315840-6209258 5250988846733325312 19.21±1.24 (Schneider et al 2019) 99.9 HD 42270 4621305817457618176 16.7±0.6 (Torres et al 2006) 99.9 2MASS J08063608-7444249 5213934514587912320 17.0±1.04 (Gaia Collaboration et al 2018) 99.7 HD 37402 4759444786175885824 23.7±0.5 (Gontcharov 2006) 99.7 HD 298936 5356713413789909632 18.4±0.44 (Gaia Collaboration et al 2018) 99.6 m Car 5251098523021221376 20.0±4.0 (Gontcharov 2006) 99.6 2MASS J06262199-7516404 5261554496328279552 16. 45±2.18 (Gaia Collaboration et al 2018) 99 (Schneider et al 2019) 96.9 2MASS J07065772-5353463 5491506843495850240 22.57±0.9 (Schneider et al 2019) 96.2 WISE J080822.18-644357.3 5277096097486882560 22.7±0.5 (Murphy et al 2018) 95.1 2MASS J07013884-6236059 5286760525517037568 22.57±0.72 (Schneider et al 2019) 94 -7844471 4625883599760005760 14.25±0.86 (Gaia Collaboration et al 2018) 86.3 2MASS J08194309-7401232 5219983787046519168 26.24±1.54 (Schneider et al 2019) 82.7 HD 95086 5231963962676292224 17.0±2.0 (Moór et al 2013b) 70.8 TYC 9200-446-1 5219351911459314048 18.01±1.48 (Gaia Collaboration et al 2018) 57.5 Table 1. HD 95086 and potential members of Carina (as identified in section 2 and ordered by their membership probability) with their radial velocities, radial velocity source and probability of membership as determined by BANYAN Σ.…”

“…Note that WISE J080822.18-644357.3 is not included here (Murphy et al 2018). show that the PARSEC isochrones do not give a good fit for this particular star.…”

NGTS-7Ab: an ultrashort-period brown dwarf transiting a tidally locked and active M dwarf

“…Chabrier et al 1996) and is typically removed from their photosphere within 45-50 Myr (see Fig. 4 of Murphy et al 2018). We do not find any sign of Li 6708Å absorption in our HARPS spectra, consistent with our estimate of 55 +80 −30 Myr and it suggests that the system cannot be much younger than this if scenario (i) is true.…”