http://arxiv.org/abs/2301.07039
We report the detection of large-amplitude, rapid radial velocity (RV) variations and line-splitting in high-resolution Keck/NIRSPEC spectra of the M9 dwarf LP 413-53. We attribute these features to binary motion. Analyzing data spanning 9 months, we infer an orbital period of 0.852725$^{+0.000002}{-0.000003}$~day, an eccentricity of 0.080$^{+0.020}{-0.013}$, a primary RV semi-amplitude of 24.2$^{+1.8}{-1.4}$ km~s$^{-1}$, and a secondary RV semi-amplitude of 29.4$^{+2.2}{-1.7}$ km~s$^{-1}$, implying a system mass ratio $M_\mathrm{secondary}$/$M_\mathrm{primary}$ = 0.822$^{+0.009}_{-0.008}$. These measurements identify LP 413-53 as the shortest-period ultracool binary discovered to date, and one of the smallest separation main sequence binaries known. The position and velocity of the system rules out previously reported membership in the Hyades Moving Group, and indicate that this is likely a pair of evolved (age $\gtrsim$ 1 Gyr), very-low-mass stars. Assuming masses consistent with evolved late-M and L dwarfs, we estimate an orbital separation of 0.0093-0.0095~au or 19-22 stellar radii, and an orbital inclination angle of 27$\pm$2 deg, making it unlikely that this system exhibits eclipse events. The larger radii of these stars at young ages would have put them in contact at the system’s current separation, and we speculate that this system has undergone dynamical evolution, either through orbital angular momentum loss or ejection of a third component followed by tidal circularization.
C. Hsu, A. Burgasser and C. Theissen
Wed, 18 Jan 23
125/133
Comments: 13 pages, 3 figures. Submitted to ApJ Letters; comments welcome