Auriga (constellation) - Notable Features - Stars - Eclipsing Binary Stars

Eclipsing Binary Stars

The most prominent variable star in Auriga is Epsilon Aurigae (Al Maz, Almaaz), an F0 class eclipsing binary star with an unusually long period of 27 years; its last minima occurred from 1982–1984 and 2009–2011. The distance to the system is disputed, variously cited as 4600 and 2170 light-years. The primary is a white supergiant, and the secondary may be itself a binary star within a large dusty disk. Its maximum magnitude is 3.0, but it stays at a minimum magnitude of 3.8 for around a year; its most recent eclipse began in 2009. The primary has an absolute magnitude of −8.5 and an unusually high luminosity of 200,000 L_☉, the reason it appears so bright at such a great distance. Epsilon Aurigae is the longest-period eclipsing binary currently known. The first observed eclipse of Epsilon Aurigae occurred in 1821, though its variable status was not confirmed until the eclipse of 1847–1848. From that time forward, many theories were put forth as to the nature of the eclipsing component. Epsilon Aurigae has a noneclipsing component, which is visible as a 14th magnitude companion separated from the primary by 28.6 arcseconds. It was discovered by Sherburne Wesley Burnham in 1891 at the Dearborn Observatory, and is about 0.5 light-years from the primary.

Another eclipsing binary in Auriga, part of the Haedi asterism with Epsilon Aurigae, is Zeta Aurigae (Sadatoni), an eclipsing binary star at a distance of 776 light-years with a period of 2 years and 8 months. It has an absolute magnitude of −2.3. The primary is an orange-hued K5II-type star (K-type bright giant) and the secondary is a smaller blue star similar to Regulus; its period is 972 days. The secondary is a B7V-type star, a B-type main-sequence star. Zeta Aurigae's maximum magnitude is 3.7 and its minimum magnitude is 4.0. The full eclipse of the small blue star by the orange giant lasts 38 days, with two partial phases of 32 days at the beginning and end. The primary has a diameter of 150 D_☉ and a luminosity of 700 L_☉; the secondary has a diameter of 4 D_☉ and a luminosity of 140 L_☉. Zeta Aurigae was spectroscopically determined to be a double star by Antonia Maury in 1897 and was confirmed as a binary star in 1908 by William Wallace Campbell. The two stars orbit each other about 500,000,000 miles (800,000,000 km) apart. Zeta Aurigae is moving away from Earth at a rate of 8 miles (13 km) per second. The last star in the asterism is Eta Aurigae, a B3 class star located 243 light-years from Earth with a magnitude of 3.17. It is a B3V class star, meaning that it is a blue-white hued main-sequence star. Eta Aurigae is a part of the Haedi or "Kids" asterism, along with Zeta and Epsilon Aurigae. Eta Aurigae has an absolute magnitude of −1.7 and a luminosity of 450 L_☉. Eta Aurigae is moving away from Earth at a rate of 4.5 miles (7.2 km) per second.

T Aurigae (Nova Aurigae 1891) was a nova discovered at magnitude 5.0 on January 23, 1892, by Thomas David Anderson. It became visible to the naked eye by December 10, 1891, as shown on photographic plates examined after the nova's discovery. It then brightened by a factor of 2.5 from December 11 to December 20, when it reached a maximum magnitude of 4.4. T Aurigae faded slowly in January and February 1892, then faded quickly during March and April, reaching a magnitude of 15 in late April. However, its brightness began to increase in August, reaching magnitude 9.5, where it stayed until 1895. Over the subsequent two years, its brightness decreased to 11.5, and by 1903, it was approximately 14th magnitude. By 1925, it had reached its current magnitude of 15.5. When the nova was discovered, its spectrum showed material moving at a high speed towards Earth. However, when the spectrum was examined again in August 1892, it appeared to be a planetary nebula. Observations at the Lick Observatory by Edward Emerson Barnard showed it to be disc-shaped, with clear nebulosity in a diameter of 3 arcseconds. The shell had a diameter of 12 arcseconds in 1943. T Aurigae is classified as a slow nova, similar to DQ Herculis. Like DQ Herculis, WZ Sagittae, Nova Persei 1901 and Nova Aquilae 1918, it is a very close binary with a very short period. T Aurigae's period of 4.905 hours, comparable to DQ Herculis's period of 4.65 hours, and has a partial eclipse period of 40 minutes.