a white dwarf and a red dwarf, is very likely to have two planets causing variations in the period of the eclipses. Although it does not have a planet, the solar analog HD 137510 has been found to have a brown dwarf companion within the brown-dwarf desert. PSR B1534+11 is a system consisting of two neutron stars orbiting each other, one of which is a pulsar with a period of 37.9 milliseconds. Situated approximately 1000 parsecs distant, the system was used to test Albert Einstein's theory of general relativity, validating the system's relativistic parameters to within 0.2% of values predicted by the theory. The X-ray emission from the system has been found to be present when the non-pulsar star intersects the equatorial pulsar wind of the pulsar, and the system's orbit has been found to vary slightly. Tail stars The brightest star in the tail, Eta Serpentis, is similar to Alpha Serpentis' primary in that it is a red giant of spectral class K. This star, however, is known to exhibit solar-like oscillations over a period of approximately 2.16 hours. The other two stars in Serpens Cauda forming its asterism are Theta and Xi Serpentis. Xi, where the asterism crosses over to Mu Serpentis in the head, is a triple star system located approximately 105 parsecs away. Two of the stars, with a combined apparent magnitude of around 3.5, form a spectroscopic binary with an angular separation of only 2.2 milliarcseconds, and thus cannot be resolved with modern equipment. The primary is a white giant with an excess of strontium. Theta, forming the tip of the tail, is also a multiple system, consisting of two A-type main-sequence stars with a combined apparent magnitude of around 4.1 separated by almost half an arcminute. There is also a third G-type star with a mass and radius similar to that of the Sun. Lying near the boundary with Ophiuchus are Zeta, Nu, and Omicron Serpentis. All three are 4th-magnitude main-sequence stars, with Nu and Omicron being of spectral type A and Zeta being of spectral type F. Nu is a single star with a 9th-magnitude visual companion, while Omicron is a Delta Scuti variable with amplitude variations of 0.01 magnitudes. In 1909, the symbiotic nova RT Serpentis appeared near Omicron, although it only reached a maximum magnitude of 10. The star system 59 Serpentis, also known as d Serpentis, is a triple star