1999AJ....117..541L

V907 Scorpii, near the open cluster M7, and possibly a member, is unique among all known eclipsing binary stars because its eclipses have turned on and off twice within modern history. By using all available photometric and spectroscopic data, we have discovered that it is at least a triple star and possibly a quadruple star system consisting of a visual binary with a very long orbital period, the brighter member of which is itself the triple star. The triple star contains an eclipsing binary star (B9.5 V) with an orbital period of 3.78 days and a faint, distant companion (late K, or perhaps a white dwarf) with an orbital period of 99.3 days around the center of mass of the triple star system. Radial velocity measurements allow the masses to be estimated. Because the orbital planes of the eclipsing binary and its triple companion are not coplanar, the orbital plane of the eclipsing binary shows nodal regression with a period of 68 yr. For about one-third of this time, the close binary is eclipsing; the rest of the time the inclination is too small for eclipses to occur. The earliest observations of the system in the year 1899 show eclipses; the eclipses stopped about 1918, started again about 1963, and stopped again in about 1986. We predict that the eclipses should start occurring once again in the year 2030±5.