binaries are one of primary sources of our knowledge
of the fundamental stellar properties.
It is well-known that these binaries are classified into two subtypes (Binnendijk, 1970).
If the more massive component is eclipsed by the less massive one at primary minimum, the system is called A-type.
On the other hand, a system with the opposite feature is called W-type.
Some authors suggested that W-type systems have evolved from A-type ones by mass loss (e.g. Gazeas and Niarchos, 2006; Rucinski, 1985),whereas others argued the opposite (e.g. Maceroni et al., 1985;Hilditch et al., 1988).