1997/10/27 by M. R. Zapatero Osorio, R. Rebolo, R. Rébolo +9 · 4 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/311073
16 pages, 2 figures, aasms4 macro in LateX. 1997 ApJ Letters, accepted
arxiv created 1997/10/27 · openalex publication_date 1997/12/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/04
We present intermediate- and low-resolution optical spectroscopy (650-915 nm) of seven faint, very red objects (20> I ≥17.8, I - Z ≥ 0.5) discovered in a CCD-based IZ survey covering an area of 1 deg 2 in the central region of the Pleiades open cluster. The observed spectra show that these objects are very cool dwarfs having spectral types in the range M6-M9. Five out of the seven objects can be considered Pleiades members on the basis of their radial velocities, Hα emissions, and other gravity-sensitive atomic features like the Na I doublet at 818.3 and 819.5 nm. According to current evolutionary models, the masses of these new objects range from roughly 80 M Jup for the hottest in the sample down to 45 M Jup for Roque 4, the coolest and faintest confirmed member. These observations prove that the cloud fragmentation process extends well into the brown dwarf realm, suggesting a rise in the initial mass function below the substellar limit.