Separate Spectra of the Components of the Low‐Mass BinariesRoss 614A,B and L722−22A,B

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ABSTRACTThe Hubble Space Telescope Faint Object Spectrograph has been used to acquire separate spectra of each of the component stars in the binaries Ross 614A,B (Gl 234A,B) and L722−22A,B (GJ 1005). Spectral types have been determined for each: M4.0 V, M5.5 V, M3.5 V, and M5.0 V, respectively, relative to a series of ground‐based CCD spectra, in the 6500–8000 Å region. The four members of the two binaries form a narrow locus in the spectral type–mass plane, from 0.18 to 0.08 M⊙ and reaching 0.08 M⊙ near spectral type M6.0. Both binaries are believed to be members of a relatively young disk population. Their masses and newly determined spectra imply that the apparently single M dwarf stars, of a similar population and with spectral types of M6, are likely to be near, or less massive than, 0.08 M⊙. Presumably, dwarf M7, M8, and M9 stars of a similar age and population are in a declining mass sequence and thus should reach well below the theoretical main‐sequence mass limit of 0.08 M⊙ and by current theory are substellar or “brown dwarf” objects.