Study investigates a nearby M-dwarf binary system

Using the Very Long Baseline Array (VLBA), astronomers have explored a nearby binary stellar system composed of two M dwarfs, known as LP 349−25AB. Results of the study, presented April 25 on the pre-print server arXiv, shed more light on the properties of this system, suggesting that one of its components may be a brown dwarf.

At a distance of only 47 light years LP 349−25 (also known as LSPM J0027+2219 or 2MASS J0027559+221932) is a binary system consisting of two M dwarf of spectral type M8V and M9V, separated by 1.2 AU. The system has a combined mass of about 166 Jupiter masses, orbital period of approximately 7.7 years, and is estimated to be 140–190 million years old.

Now, a team of astronomers led by Salvador Curiel of the National Autonomous University (UNAM) of Mexico, has performed very long baseline interferometry (VLBI) observations of LP 349−25, finding that the system is less massive and older than previously thought. The observational campaign was carried out with VLBA between February 2020 and December 2021.

“Here, we report 5 GHz VLBA observations of the binary LP 349−25AB from 11 epochs spanning 1.8 years. (…) Two epochs were observed at 4.85 GHz using eight 32-MHz frequency bands, in dual polarization mode, with a data rate recording of 2 Gbps. The remaining nine epochs were observed with four 128-MHz frequency bands and the 4 Gbps recording rate,” the researchers wrote in the research paper.

The collected VLBA data show that both components of LP 349−25AB are radio emitters, with the primary star LP 349−25A being the dominant radio emitter. It turned out that the primary star presents a small temporal flux density variation over a time span of months, while its companion does not show radio flux density variation. No circular polarization, nor outbursts have been observed from both stars.

By combining the VLBA results with the existing optical/infrared relative astrometric data, Curiel’s team was able to precisely determine the mass of LP 349−25AB. They found that the primary component has a mass of 85.71 Jupiter masses, while the mass of the secondary object is 67.11 Jupiter masses—thus below the expected mass limit of hydrogen burning (about 78.5 Jupiter masses) and consistent with being a substellar object like a brown dwarf.

Furthermore, using stellar evolutionary tracks the astronomers found that the cooling age of LP 349−25A is 262 million years, while the cooling age of LP 349−25B is 198 million years. These results suggest that the primary star is an ultra compact dwarf (UCD) and its companion may be a brown dwarf. The distance to the system was measured to be approximately 46 light years.

Given that the brown dwarf status is yet unconfirmed, the authors of the paper noted that LP 349−25AB is currently the nearest pre-main-sequence binary system containing very low mass stars with direct mass measurements. According to the researchers, their study proves that precise stellar parameters of each star can be obtained by using stellar evolutionary models.

© 2024 Science X Network