Fig11_5 (left)Sirius

Fig11_5 (left)Sirius

Fig. 11.5 . The brightest star in the night sky, called the Dog Star and also designated Sirius A, has a faint companion Sirius B. This binary star system is located just 8.6 light-years from the Earth. Sirius A is a main-sequence star with twice the mass of the Sun, and a disk temperature of 9,940 K. Its white-dwarf companion, Sirius B, has 98 percent the mass of the Sun and a disk temperature of 25,200 K. Owing to its small size, comparable to that of the Earth, Sirius B is a thousand times less luminous that Sirius A. The faint white dwarf can be seen in the lower left of the Hubble Space Telescope image taken in optically visible light (left): the cross-shaped diffraction spikes and concentric rings around the much brighter Sirius A are artifacts produced by the telescope imaging system. Sirius B is somewhat brighter in X-rays due to its higher temperature, as indicated in the Chandra X-ray Observatory image (right). [Courtesy of NASA/H. E. Bond and E. Nelan, STScI/M. Barstow and M. Burleigh, U. Leicester/ and J. B. Holberg, U. Az (left) and NASA/SAO/CXO (right).]

Copyright 2010, Professor Kenneth R. Lang, Tufts University