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 very compact: a neutron star or black hole. The infalling matter releases gravitational potential energy, up to several tenths 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.
A stellar black hole is a black hole formed by the gravitational collapse of a star. They have masses ranging from about 5 to several tens of solar masses. The process is observed as a hypernova explosion or as a gamma ray burst. These black holes are also referred to as collapsars.
Sagittarius A* is a bright and very compact astronomical radio source at the Galactic Center of the Milky Way. It is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic, visually close to the Butterfly Cluster (M6) and Shaula. Sagittarius A* is the location of a supermassive black hole, similar to massive objects at the centers of most, if not all, spiral and elliptical galaxies.
SS 433 is one of the most exotic star systems observed. It is located in the Milky Way galaxy, and is an eclipsing X-ray binary system, with the primary being a stellar-mass black hole. The spectrum of the secondary companion star suggests that it is a late A-type star. SS 433 is the first discovered microquasar. It is at the centre of the supernova remnant W50.
V1494 Aquilae or Nova Aquilae 1999 b was a nova which occurred during 1999 in the constellation Aquila and reached a brightness of magnitude 3.9 on 2 December 1999. making it easily visible to the naked eye. The nova was discovered with 14×100 binoculars by Alfredo Pereira of Cabo da Roca, Portugal at 18:50 UT on 1 December 1999, when it had a visual magnitude of 6.0.
X Sagittarii is a variable star and candidate binary star system in the southern constellation of Sagittarius, near the western constellation boundary with Ophiuchus. It has a yellow-white hue and is visible to the naked eye with an apparent visual magnitude that fluctuates around 4.54. The star is located at a distance of approximately 950 light years from the Sun based on parallax, and is drifting closer with a radial velocity of −10 km/s. The star has an absolute magnitude of around −2.85.
Nu¹ Sagittarii is a triple star system about 1,100 light-years from Earth. Its three components are designated Nu¹ Sagittarii A, B and C. A and B themselves form a spectroscopic binary. The system is 0.11 degree north of the ecliptic.
Psi Sagittarii, which is Latinized from ψ Sagittarii, is a triple star system in the zodiac constellation of Sagittarius. The star system is located at a distance of 298 light years from the Earth based on parallax, but is drifting closer with a heliocentric radial velocity of −12 km/s. The system is faintly visible to the naked eye has a combined apparent visual magnitude of +4.86.
KW Sagittarii is a red supergiant, located approximately 1,900 parsecs away from our Sun in the direction of the constellation Sagittarius. It is one of the largest-known stars. If placed at the center of the Solar System, the star's surface would engulf Mars.
V1057 Cygni is a suspected binary star system in the northern constellation of Cygnus. It is a variable star of the FU Orionis-type, and was the second FU Orionis-type variable to be discovered. The system is located at a distance of approximately 3,000 light years from the Sun, in the North America Nebula. It has an apparent visual magnitude of around 12.4.
A0620-00 is a binary star system in the constellation of Monoceros.
V4381 Sagittarii is a variable star in the constellation Sagittarius. A white supergiant of spectral type A2/A3Iab, it is an Alpha Cygni variable that varies between apparent photographic magnitudes 6.57 and 6.62. Its visual apparent magnitude is about 6.54.
9 Sagittarii is a massive binary star in the constellation Sagittarius. It has an apparent magnitude of 5.97.
V1017 Sagittarii is a cataclysmic variable star system in the constellation Sagittarius. It first erupted in 1919, reaching magnitude 7. Its other eruptions in 1901, 1973 and 1991 only reached magnitude 10, leading it to be reclassified from a recurrent nova to a dwarf nova.
V4743 Sagittarii was a bright nova in the southern constellation of Sagittarius. This event was discovered by K. Haseda and colleagues in September 2002. It peaked at magnitude 5.0 on September 20, 2002, then declined rapidly thereafter. It reached a peak temperature of 740,000 K around April 2003 and remained at that level for at least five months, suggesting the white dwarf component has a mass of 1.1–1.2 M☉. The distance to this system is uncertain. Infrared observations indicate a distance of approximately 21 kly (6.3 kpc). A derivation using maximum magnitude rate of decay showed a distance of 12.7 ± 1.0 kly (3.9 ± 0.3 kpc).
SU Ursae Majoris, or SU UMa, is a close binary star in the northern circumpolar constellation of Ursa Major. It is a periodic cataclysmic variable that varies in magnitude from a peak of 10.8 down to a base of 14.96. The distance to this system, as determined from its annual parallax shift of 4.53 mas, is 719 light-years. It is moving further from the Earth with a heliocentric radial velocity of +27 km/s.
Aquila X-1 is a low-mass x-ray binary (LMXB) and the most luminous X-Ray source in the constellation Aquila. It was first observed by the satellite Vela 5B which detected several outbursts from this source between 1969 and 1976. Its optical counterpart is variable, so it was named V1333 Aql according to the IAU standards. The system hosts a neutron star that accretes matter from a main sequence star of spectral type K4. The binary's orbital period is 18.9479 hours.
EG Andromedae is a symbiotic binary in the constellation Andromeda. Its apparent visual magnitude varies between 6.97 and 7.80.
AK Scorpii is a Herbig Ae/Be star and spectroscopic binary star about 459 light-years distant in the constellation Scorpius. The star belongs to the nearby Upper Centaurus–Lupus star-forming region and the star is actively accreting material. The binary is surrounded by a circumbinary disk that was imaged with VLT/SPHERE in scattered light and with ALMA.
V4332 Sagittarii is a nova-like event in the constellation of Sagittarius. It was discovered February 24, 1994 at an apparent visual magnitude of 8.9 by Japanese amateur astronomer Minoru Yamamoto from Okazaki, Aichi, then confirmed by K. Hirosawa. Initially designated Nova Sagittarii 1994 #1, it was given the variable star designation V4332 Sgr. A spectra of the event taken March 4 lacked the characteristic features of a classical nova, with the only emission lines being of the Balmer series. Subsequent spectra showed a rapid decline in luminosity and a change of spectral type over a period of five days. By 2003, the object was ~1500 times less luminous than at peak magnitude and showed a spectrum of an M-type star.
