GJ 900: A new hierarchical system with low-mass components

Abstract

Speckle interferometric observations made with the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in 2000 revealed the triple nature of the nearby (${\pi }_{Hip}=51.80\pm 1.74$ mas) low-mass young ($\approx 200$ Myr) star GJ 900. The configuration of the triple system allowed it to be dynamically unstable. Differential photometry performed from 2000 through 2004 yielded $I$- and $K$-band absolute magnitudes and spectral types for the components to be $I_A$=6.66$\pm$0.08, $I_B$=9.15$\pm$0.11, $I_C$=10.08$\pm$0.26, $K_A$=4.84$\pm$0.08, $K_B$=6.76$\pm$0.20, $K_C$=7.39$\pm$0.31, $S{p}_A$$\approx$K5--K7, $S{p}_B$$\approx$M3--M4, $S{p}_C$$\approx$M5--M6. The ``mass--luminosity'' relation is used to estimate the individual masses of the components: ${\mathcal{M}}_A$$\approx 0.64{\mathcal{M}}_{\odot }$, ${\mathcal{M}}_B$$\approx 0.21{\mathcal{M}}_{\odot }$, ${\mathcal{M}}_C$$\approx 0.13{\mathcal{M}}_{\odot }$. From the observations of the components relative motion in the period 2000--2006, we conclude that GJ 900 is a hierarchical triple star with the possible orbital periods P${}_{A-BC}$$\approx$80 yrs and P${}_{BC}$$\approx$20 yrs. An analysis of the 2MASS images of the region around GJ 900 leads us to suggest that the system can include other very-low-mass components.

7 pages, 5 figures

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