SDSS J111010.01+011613.1: A New Planetary-Mass T Dwarf Member of the AB Doradus Moving Group (1506.04195v1)

Abstract: We present a new radial velocity measurement that, together with a trigonometric parallax, proper motion and signs of low gravity from the literature, confirms that SDSS J111010.01+011613.1 is a new T5.5 bona fide member of AB Doradus. Fitting $\lambda/\Delta\lambda$ $\approx$ 6000 FIRE spectroscopy in the 1.20-1.33 $\mu$m region to BT-Settl atmosphere models yielded a radial velocity of $7.5 \pm 3.8$ km s$^{-1}$. At such a young age (110-130 Myr), current evolution models predict a mass of $\sim$ 10-12 $M_{\mathrm{Jup}}$, thus placing SDSS J1110+0116 well into the planetary-mass regime. We compare the fundamental properties of SDSS J1110+0116 with a sequence of seven recently identified M8-T5 brown dwarf bona fide or high-confidence candidate members of AB Doradus. We also note that its near-infrared $J-K$ color is redder than field T5-T6 brown dwarfs, however its absolute $J$-band magnitude is similar to them. SDSS J1110+0116 is one of the few age-calibrated T dwarfs known to date, as well as one of the coolest bona fide members of a young moving group.

SDSS J111010.01+011613.1: A New T Dwarf Member of the AB Doradus Moving Group

The paper presented investigates the identification of a new planetary-mass brown dwarf, SDSS J111010.01+011613.1 (SDSS J1110+0116), as a bona fide member of the AB Doradus moving group. This object is of spectral type T5.5 and represents one of the rare age-calibrated T dwarfs within this young association, providing a critical data point for the characterization of substellar objects near the low-mass end of the initial mass function.

Key Findings and Methodology

The authors employ an integrative approach, using radial velocity measurements and a suite of pre-existing astrometry from trigonometric parallax to confirm membership of SDSS J1110+0116 in the AB Doradus moving group. A radial velocity of $7.5 \pm 3.8$ km/s was obtained from FIRE spectroscopy, consistent with AB Doradus membership predictions. The analysis also incorporated atmospheric modeling to estimate surface gravity and effective temperature, asserting low gravity signatures that substantiate the youth of the object.

As per evolutionary models for young systems, SDSS J1110+0116 has an inferred mass in the range of 10 to 12 Jupiter masses, categorizing it firmly within the planetary-mass regime. Furthermore, it is noted for having $J-K$ colors redder than typical field T dwarfs, while its absolute $J$-band magnitude remains comparable, suggesting peculiar atmospheric properties perhaps related to enhanced dust opacity caused by low gravity.

Implications

This discovery has significant implications for the astrophysical paper of low-mass brown dwarfs and giant exoplanets. As a cool member of the AB Doradus group, SDSS J1110+0116 offers unique insights into atmospheric dynamics under low gravitational conditions and can provide benchmarks for the evolutionary models of planetary-mass objects. Moreover, the proximity and brightness render it a feasible target for follow-up observations with next-generation telescopes, such as the James Webb Space Telescope and other large observatories.

Future Directions

The detection of SDSS J1110+0116 prompts further investigation into similar substellar objects, potentially uncovering more isolated brown dwarfs or planetary-mass companions within young moving groups. Such studies could refine our understanding of atmospheric processes and mass evolution across different spectral types and ages. The integration of models that account for magnetic fields or alternative formation hypotheses, like cold start models, might also address systematic uncertainties observed in currently applied models.

In conclusion, this paper enriches the field of brown dwarf and exoplanet research, providing a valuable reference point in the AB Doradus moving group for future observational campaigns and theoretical models concerning young, planetary-mass objects.