We present VLT-FORS2 optical ( 5700 - 9400 Å ) spectroscopy of close ( r < 1.5 ” ) companions to three nearby ( d < 200 pc ) Herbig Ae/Be stars ( HD 144432 , HD 150193 , KK Oph ) and one T Tauri star ( S CrA ) .
We report the detection of Li I ( 6707 Å ) in absorption and emission lines ( H _ { \alpha } , Ca II triplet ) in the spectra of the companions .
Our observations strongly suggest that the companions are physically associated pre-main-sequence stars .
The spectral type derived for the companions is K5Ve for HD 144432 B , F9Ve for HD 150193 B , and G6Ve for KK Oph B .
S CrA A and B were observed simultaneously .
The spatially resolved spectra indicate that S CrA A ( primary , north ) is a G star and that S CrA B ( secondary , south ) is a K star .
Using photometry from the literature and estimations of the R and I magnitude derived from the spectra , we localized primaries and companions in the HR diagram , derived their masses and assuming coevality constrained the age of the systems .
KK Oph B ( 7 Myr ) and S CrA B ( 2 Myr ) are actively accreting T Tauri stars and are very likely surrounded by disks .
HD 150193 B ( 10 Myr ) and HD 144432 B ( 8 Myr ) are weak-line T Tauri stars .
Three of the four systems studied ( HD 144432 , HD 150193 , KK Oph ) have ages > 7 Myr .
These systems retained their disks for a longer time than typical of a young star .
Our results suggest that binarity may be a key issue in understanding the lifetime of disks .