The DH Leo system consists of an active BY Draconis binary plus a more distant tertiary component. Contemporaneous optical, ultraviolet spectra, and photometric observations were obtained during the spring of 1987. Excess emission was detected in the activity sensitive lines of Hα, Hβ, Hγ, Hδ, and the Ca II H and IRT lines. Phase modulation was seen for Hα, Hβ, and the Ca II lines. Correlation of the emission-line modulation with the photometric modulation suggests that the emission is concentrated in plage-like regions associated with cool star spots, but it is apparent that there is also some global chromospheric emission since in comparison to earlier epochs the photometric modulation has decreased more than the Ha excess emission. The possible detection of a depression in the emission modulation near primary conjunction suggests the existence of extended material on the secondary occulting an emission region on the primary. The Balmer emission differs from that of RS CVn systems in that the Hα/Hβ ratio is much lower than found in the longer period RS CVn systems. This is best explained by the system having a main-sequence primary instead of an evolved primary (as in RS CVn systems), leading to a denser emitting region due to the higher-pressure atmosphere. The UV emission lines are variable but due to a lack of adequate phase coverage the origin of the activity cannot be ascertained.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science