A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, because gases or other material may be falling from the inner edge of the disk onto the surface of the star. This process should not be confused with the accretion process thought to build up the planets themselves. Externally illuminated photo-evaporating protoplanetary disks are called proplyds.
Epsilon Sagittarii, formally named Kaus Australis, is a binary star system in the southern zodiac constellation of Sagittarius. The apparent visual magnitude of +1.85 makes it the brightest object in Sagittarius. Based upon parallax measurements, this star is around 143 light-years from the Sun.
Alpha Sagittarii, also named Rukbat, is a star in the constellation of Sagittarius.
HR 7703 is a binary star system in the constellation of Sagittarius. The brighter component has an apparent visual magnitude of 5.31, which means it is visible from suburban skies at night. The two stars are separated by an angle of 7.10″, which corresponds to an estimated semimajor axis of 56.30 AU for their orbit.
Eta Sagittarii is a binary star system in the southern zodiac constellation of Sagittarius. Based upon parallax measurements, it is located at a distance of 146 light-years from Earth. In India, where part of the constellation of Sagittarius represents an Elephant, this star forms the creature's tail.
Upsilon Sagittarii is a spectroscopic binary star system in the constellation Sagittarius. Upsilon Sagittarii is the prototypical hydrogen-deficient binary (HdB), and one of only four such systems known. The unusual spectrum of hydrogen-deficient binaries has made stellar classification of Upsilon Sagittarii difficult.
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.
HD 98800, also catalogued as TV Crateris, is a quadruple star system in the constellation of Crater. Parallax measurements made by the Hipparcos spacecraft put it at a distance of about 150 light-years away, but this value is in high error. The system is located within the TW Hydrae association (TWA), and has received the designation TWA 4.
UX Tauri, abbreviated as UX Tau, is a binary star system approximately 450 light-years away in the constellation of Taurus. It is notable for the fact that, despite its recent creation, the Spitzer Space Telescope discovered that its protoplanetary disk contains a gap. The dust, which normally accumulates in an expanding ring starting right next to the star at such a young age, is either very thin or nonexistent at a range of 0.2 to 56 AU from the star. Typically, this means that the early ancestors of planets may be forming from the disk, though the star only ignited about 1 million years ago. In contrast, Earth was formed approximately 4.54 billion years ago, placing its formation about sixty million years after the Sun's ignition around 4.6 billion years ago.
9 Sagittarii is a massive binary star in the constellation Sagittarius. It has an apparent magnitude of 5.97. Both components are highly luminous O-type main-sequence stars.
GG Tauri, often abbreviated as GG Tau, is a quintuple star system in the constellation Taurus. At a distance of about 450 light years away, it is located within the Taurus-Auriga Star Forming Region. The system comprises three stars orbiting each other in a hierarchical triple system, known as GG Tauri A, and another binary star system more distant from the central system, known as GG Tauri B.
KH 15D, described as a winking star because of its unusual dips in brightness, is a binary T Tauri star system embedded in a circumbinary disk. It is a member of the young open cluster NGC 2264, located about 2,500 light-years (770 pc) from the Sun in the constellation of Monoceros.
A circumplanetary disk is a torus, pancake or ring-shaped accumulation of matter composed of gas, dust, planetesimals, asteroids or collision fragments in orbit around a planet. Around the planets, they are the reservoirs of material out of which moons may form. Such a disk can manifest itself in various ways.
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.
RW Aurigae is a young binary system in the constellation of Auriga about 530 light years away, belonging to the Taurus-Auriga association of the Taurus Molecular Cloud. RW Aurigae B was discovered in 1944.
HK Tauri is a young binary star system in the constellation of Taurus about 434 light-years away, belonging to the Taurus Molecular Cloud.
GK Tauri is a young T Tauri-type pre-main sequence star in the constellation of Taurus about 421 light years away, belonging to the Taurus Molecular Cloud.
CQ Tauri is a young variable star in the equatorial constellation of Taurus. It is too faint to be visible to the naked eye with an apparent visual magnitude that ranges from 8.7 to 12.25. The distance to this star is approximately 487 light years based on parallax measurements, and it is drifting further away with a radial velocity of ~23 km/s. It appears to be part of the T-association Tau 4. CQ Tauri lies close enough to the ecliptic to undergo lunar occultations.
RS Sagittarii is an eclipsing binary star system in the southern constellation of Sagittarius, abbreviated RS Sgr. It is a double-lined spectroscopic binary with an orbital period of 2.416 days, indicating that the components are too close to each other to be individually resolved. The system has a combined apparent visual magnitude of 6.01, which is bright enough to be faintly visible to the naked eye. During the primary eclipse the brightness drops to magnitude 6.97, while the secondary eclipse is of magnitude 6.28. The distance to this system is approximately 1,420 light years based on parallax measurements.
