Individual dynamical masses of DENIS J063001.4−184014AB reveal a likely young brown dwarf triple

Abstract

The binary nature of the M8.5 dwarf DENIS J063001.4−184014AB (DE0630−18) was discovered with astrometric monitoring from the ground, which determined the unresolved photocentric orbit and the trigonometric parallax of the system. Here we present radial-velocity monitoring and resolved observations in the near-infrared with Keck aperture masking that allow us to measure the system’s relative separation and brightness. By combining all available information, we determine the individual dynamical masses of the binary components to be $M_1 = 0.052^{+0.009}_{-0.008}$ MSun and $M_2 = 0.052^{+0.005}_{-0.004}$ MSun, both firmly in the substellar regime. These masses are surprising given the object’s M8.5 optical spectral type and equivalent absolute magnitude, and the significant difference in brightness between the components (ΔK = 1.74±0.06 mag). Our results suggest that DE0630−18 is a relatively young system (∼200 Myr) with a secondary component that is itself a potentially unresolved binary.

The Brown Dwarf Kinematics Project (BDKP). V. Radial and Rotational Velocities of T Dwarfs from Keck/NIRSPEC High-resolution Spectroscopy

“…The resulting ages for late M, L, and T dwarfs in these simulations are 4.1 ± 0.8 Gyr, 4.1 ± 0.8 Gyr, and 4.4 ± 1.2 Gyr, respectively, fully consistent with our observed ages (Figure 28). The fact that this adjustment provides the best match between the simulations and observed sources is suggestive of potential evolutionary model issues, which have also been raised with mass and luminosity measurements of brown dwarf companions to age-dated stars ) and the surprisingly high-mass T-type brown dwarfs in binaries (e.g., Dupuy et al 2019;Brandt et al 2020;Sahlmann et al 2020Sahlmann et al , 2021. These studies suggest that evolutionary model predictions of the temperatures and luminosities of objects around the HBMM may not align with the observed properties of these systems.…”

New constraints on the minimum mass for thermonuclear lithium burning in brown dwarfs

“…The upper limit on the presence of the Li I in Sahlmann 2 AB is rather conservative because in fact we could not see any feature whose pseudo-equivalent width is pEW ≥ 0.1 Å around 670.8 nm in any of the spectra. Our adopted upper limit of 0.17 Å on the pEW of the Li I resonance doublet in Sahlmann 2 AB improves the sensitivity to lithium detection in Sahlmann 2 AB by a factor of almost six times over the upper limit of 1 Å reported in Sahlmann et al (2021) from a noisy (SNR < 3) high-resolution UVES spectrum obtained with the European Southern Observatory Very Large Telescope.…”

“…To convert the adopted upper limit pEW Li I of < 0.17 Å for the combined light of the Sahlmann 2 AB system into lithium detection limits for each component, the individual contributions to the flux around the spectral region of the Li I resonance doublet are needed. Sahlmann et al (2021) estimated ∆IFORS2 = 2.8±0.5 mag from a Keck adaptive optics assisted spatially resolved imaging observation that gave ∆KNIRC2 = 1.74±0.06 mag. These authors also carried out binary fitting of the low-resolution near-infrared spec- The second step is to estimate the upper limits on the pEW Li I for each component.…”

“…Here we focus on DENIS J063001.4−184014AB (hereafter Sahlmann 2 AB, inspired by the Washington Double Star catalog convention of naming objects after the discoverer of the binary nature), which was classified as an M8.5 dwarf from optical low-resolution reconnaissance spectroscopy and it was found to be an astrometric binary with an orbital period of 3.1 years (Sahlmann et al 2015a). The dynamical mass of each component in the binary has been obtained from combining the astrometric data with spatially resolved near-infrared imaging, and radial velocities for the primary (Sahlmann et al 2021). These authors noted that there was no sign of strong Li I resonance doublet in a high-resolution optical spectrum of the system, despite the low masses of M1 = 54 +10 −9 MJup and M2 = 54 +6 −5 MJup of the components, but they could only place a upper limit of 1 Å on the measurable pseudo-equivalent width (pEW) because of low signal to noise ratio.…”

“…Dupuy & Liu (2017) considered that 2MASS J0700+3157 B could be composed of two equal mass brown dwarfs with mass of 36.7 +1.4 −1.5 MJup each. Sahlmann et al (2021) proposed that Sahlmann 2 B is made up of two unresolved brown dwarfs with mass of 25 MJup each.…”