Binary Star composed of 2 Brown Dwarfs discovered by Microlensing

Light curve of the microlensing event OGLE-2016-BLG-1469. The upper panel shows the enlarged view of the anomaly around the peak. The two lower panels show the residual from the binary-lens models with (orbit+parallax) and without (standard) considering higher-order effects. Credit: Han et al., 2017.

Using gravitational microlensing, astronomers have recently found a binary star composed of two brown dwarfs. The newly discovered system is the third brown-dwarf binary detected with this technique. Gravitational microlensing is an invaluable method of detecting new extrasolar planets and brown dwarfs, regardless of the light they emit. This technique is therefore sensitive to the mass of the objects, rather than their luminosity, which allows astronomers to study objects that emit little or no light at all. Hence, due to their extremely low luminosities, brown-dwarf systems seem to be ideal targets for microlensing observations.

Now, a team reports the detection of a new brown-dwarf binary system from the analysis of the microlensing event OGLE-2016-BLG-1469. The discovery is the result of a joint effort of over 50 scientists working in three microlensing research groups. MOA researchers employed the 1.8m telescope at the Mt. John University Observatory in New Zealand, while OGLE scientists used the 1.3m telescope located at the Las Campanas Observatory in Chile. When it comes to KMTNet, the astronomers utilized 3 identical 1.6m telescopes located at the Cerro Tololo Inter-American Observatory in Chile, the South African Astronomical Observatory in South Africa, and the Siding Spring Observatory in Australia.

All these ground-based observatories located worldwide allowed the team to find that the light curve of the microlensing event showcased a short-term central anomaly. This irregularity turned out to be produced by a binary companion with a mass roughly equal to the primary. More importantly, the researchers were able to determine the mass of both brown dwarfs and estimate their projected separation. They found that the mass of one of the newly discovered objects is about 0.05 solar masses, while the second one has ~0.01 the mass of the sun. The projected separation between the binary components was estimated to be 0.33 AU. Moreover, the study revealed that the system is 14,670 light years away from the Earth.

“By measuring both the angular Einstein radius and the microlens parallax, we could uniquely determine the masses and identified the substellar nature of the lens components,” the paper reads. Their discovery shows the importance of the microlensing technique when it comes to finding new brown-dwarf binary systems.
“The lens was the third microlensing brown-dwarf binary with measured mass, demonstrating the usefulness of the microlensing method in detecting field brown-dwarf binaries,” the researchers concluded.
https://phys.org/news/2017-05-binary-star-brown-dwarfs-microlensing.htmljCp