As early as the 1840s, Johann Friedrich Julius Schmidt believed 68 Herculis was a variable star, initially thinking it might be a long period or irregular variable. By 1869 he had concluded that its brightness varies with a regular period, but his period estimates were far longer than the true value.[9] In 1908 the star was put on an observing program at Harvard College Observatory, and professor Oliver Wendell determined that the star is an eclipsing binary with a period of 2.05 days.[10]
The inner pair of this system form a well-studied[3]semidetached binary with the orbital plane oriented near the line of sight to the Earth, making it an Algol-typeeclipsing binary. They have an orbital period of just over two days and a semimajor axis of 15 times the radius of the Sun, with the secondary component transferring mass to the hotter primary star.[5] The main eclipse reduces the magnitude of the system to 5.37, while the second eclipse lowers the brightness to magnitude 4.93.[4] Theoretical calculations suggest the donor star began with 7.2 times the mass of the Sun, the current primary at 3.6 solar masses, and their initial orbital period was around 1.35days.[5]
The secondary, component Ab or occasionally just B, has proven difficult to classify, but appears as a B-type star of type B8-9.[3] It is close to triple the mass of the Sun with 4.3 times the Sun's radius. The star is spinning with a projected rotational velocity of 105km/s. It is radiating 426.5 times the Sun's luminosity from its photosphere at an effective temperature of 12,600K.[5]
The third member of this system, component B, lies at an angular separation of 4.4″ from the inner pair with a visual magnitude of 10.2.[8] It shares a common proper motion and similar parallax to the eclipsing pair, and is modelled to be a main-sequence star somewhat more massive, hotter, and more luminous than the Sun.[12] Any orbit would require thousands of years.[13]
123456Hilditch, R. W. (April 2005), "Astrophysical parameters for the eclipsing binary u Herculis", The Observatory, 125: 72–81, Bibcode:2005Obs...125...72H
123456Kolbas, V.; Dervișoğlu, A.; Pavlovski, K.; Southworth, J. (November 2014), "Tracing CNO exposed layers in the Algol-type binary system u Her", Monthly Notices of the Royal Astronomical Society, 444 (4): 3118–3129, arXiv:1408.2681, Bibcode:2014MNRAS.444.3118K, doi:10.1093/mnras/stu1652.
12345678Saad, Somaya; Nouh, Mohamed (June 2011), "A study of the B+B double-lined eclipsing binary u Her", Bulletin of the Astromical Society of India, 39: 277–287, Bibcode:2011BASI...39..277S.
