Cygnus is a northern constellation on the plane of the Milky Way, deriving its name from the Latinized Greek word for swan. Cygnus is one of the most recognizable constellations of the northern summer and autumn, and it features a prominent asterism known as the Northern Cross. Cygnus was among the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations.
Norma is a small constellation in the Southern Celestial Hemisphere between Ara and Lupus, one of twelve drawn up in the 18th century by French astronomer Nicolas-Louis de Lacaille and one of several depicting scientific instruments. Its name is Latin for normal, referring to a right angle, and is variously considered to represent a rule, a carpenter's square, a set square or a level. It remains one of the 88 modern constellations.
X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the donor, to the other component, called the accretor, which is either a neutron star or black hole. The infalling matter releases gravitational potential energy, up to 30 percent of its rest mass, as X-rays. The lifetime and the mass-transfer rate in an X-ray binary depends on the evolutionary status of the donor star, the mass ratio between the stellar components, and their orbital separation.
Be/X-ray binaries (BeXRBs) are a class of high-mass X-ray binaries that consist of a Be star and a neutron star. The neutron star is usually in a wide highly elliptical orbit around the Be star. The Be stellar wind forms a disk confined to a plane often different from the orbital plane of the neutron star. When the neutron star passes through the Be disk, it accretes a large mass of hot gas in a short time. As the gas falls onto the neutron star, a bright flare in hard X-rays is seen.
Musca is a small constellation in the deep southern sky. It was one of 12 constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman, and it first appeared on a celestial globe 35 cm (14 in) in diameter published in 1597 in Amsterdam by Plancius and Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in Johann Bayer's Uranometria of 1603. It was also known as Apis for 200 years. Musca remains below the horizon for most Northern Hemisphere observers.
Centaurus X-3 is an X-ray pulsar with a period of 4.84 seconds. It was the first X-ray pulsar to be discovered, and the third X-ray source to be discovered in the constellation Centaurus. The system consists of a neutron star orbiting a massive, O-type supergiant star dubbed Krzemiński's star after its discoverer, Wojciech Krzemiński. Matter is being accreted from the star onto the neutron star, resulting in X-ray emission.
LS I +61 303 is a binary system containing a massive star and a compact object. The compact object is a pulsar and the system is around 7,000 light-years away.
Westerlund 1 is a compact young super star cluster about 3.8 kpc away from Earth. It is thought to be the most massive young star cluster in the Milky Way, and was discovered by Bengt Westerlund in 1961 but remained largely unstudied for many years due to high interstellar absorption in its direction. In the future, it will probably evolve into a globular cluster.
Vela X-1 is a pulsing, eclipsing high-mass X-ray binary (HMXB) system, associated with the Uhuru source 4U 0900-40 and the supergiant star HD 77581. The X-ray emission of the neutron star is caused by the capture and accretion of matter from the stellar wind of the supergiant companion. Vela X-1 is the prototypical detached HMXB.
The gamma-ray and X-ray source GRS 1124-683, discovered by the Granat mission and Ginga, is a system containing a black hole candidate. The system also goes by the name X-ray Nova Muscae 1991 or GU Muscae. These two orbiting X-ray telescopes discovered the system when the system produced an outburst of X-rays on January 9, 1991.
X Persei is a high-mass X-ray binary system located in the constellation Perseus, approximately 950 parsecs away. It is catalogued as 4U 0352+309 in the final Uhuru catalog of X-ray objects.
Eta Muscae is a multiple star system in the southern constellation of Musca. It is visible to the naked eye as a faint, blue-white hued point of light with an apparent visual magnitude of 4.79. The system is located around 406 light years away from the Sun. It is a member of the Lower Centaurs Crux subgroup of the Sco OB2 stellar association of co-moving stars.
Theta Muscae is a multiple star system in the southern constellation Musca, containing a Wolf-Rayet star and two massive companions. With an apparent magnitude of 5.5, it is the second-brightest Wolf–Rayet star in the sky, although much of the visual brightness comes from the massive companions and it is not one of the closest of its type.
R Muscae is a yellow-white hued variable star in the southern constellation of Musca. It has a nominal apparent visual magnitude of 6.31, which is near the lower limit of visibility to the naked eye. The distance to this star, as determined from its annual parallax shift of 1.00 mas, is around 3,260 light years.
S Muscae is a classical (δ) Cepheid variable star in the constellation Musca about 2,600 light years away.
SY Muscae is a binary star system in the constellation Musca composed of a red giant and a white dwarf. Its apparent magnitude varies from 10.2 to 12.7 over a period of 624.5 days. Although the binary is a symbiotic star system, it is unusual in that it does not have an eruptive component. It is an S-type symbiotic system, which means that the light comes from the stars rather than surrounding dust.
BP Crucis is an X-ray binary system containing a blue hypergiant and a pulsar.
UY Volantis, also known as EXO 0748-676, is a low mass X-ray binary system located in the constellation Volans. With an apparent magnitude of 16.9, it requires a powerful telescope to see. With a radial velocity of 20 km/s, it is drifting away from the Solar System, and is currently located 26,000 light years away.
GT Muscae, also known as 12 Muscae, is a variable star about 400 light years from the Earth, in the constellation Musca. It is a 5th magnitude star, so it should be faintly visible to the naked eye of an observer far from city lights. It is a quadruple star system, consisting of a spectroscopic binary containing an RS Canum Venaticorum variable star, orbiting an eclipsing binary. It varies in brightness from magnitude 4.96 to 5.23. GT Muscae is a very active X-ray source.
AR Piscium is a binary star system in the northern constellation of Canes Venatici, abbreviated AR Psc. It has the Henry Draper Catalogue identifier HD 8357; AR Piscium is its variable star designation. The pair have a combined apparent visual magnitude that fluctuates around 7.24, which is too faint to be readily visible to the naked eye. Parallax measurements place it at a distance of 148 light years from the Sun. The motion of this star through the Milky Way suggests it is a member of the intermediate disc population.
