2006/05/04 by E. L. Martin, E. L. Martín, W. Brandner +8 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #physics.space-ph
paper · pdf · doi:10.1051/0004-6361:20054186
accepted for publication in A&A
arxiv created 2006/05/04 · openalex publication_date 2006/08/04 · arxiv updated 2009/12/01 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/01
Using the low-resolution mode of the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST), we obtain spectra from 20 spatially-resolved, ultracool dwarfs, eighteen of which belong to nine very low-mass binary systems with known angular separations in the range 037–0098. For these dwarfs, we derive their spectral types to be in the range dM7.5 to dL6 by either obtaining their PC3 index value or by comparing our STIS spectra with ground-based spectra of similar spectral resolution from Martín et al. (1999b). We have searched for Hα emission in each object, but the emission is clearly detected in only two of them. We find that the distribution of Hα emission in our sample is statistically different from that of single field dwarfs, suggesting an intriguing anti-correlation between chromospheric activity and binarity for M7–M9.5 dwarfs. We provide strength measuments of the main photospheric features. We derive calibrations of spectral subclasses versus and K-band absolute magnitudes for a subset of 10 dwarfs in 5 binaries that have known trigonometric parallaxes.