Reflection nebula | |
---|---|
Protoplanetary nebula | |
Observation data: J2000 epoch | |
Right ascension | 06h 19m 58.2160s [1] |
Declination | −10° 38′ 14.691″ [1] |
Distance | 2.3 ± 0.3 [2] k ly (710 ± 100 pc) |
Apparent magnitude (V) | 9.02 [1] |
Constellation | Monoceros |
Physical characteristics | |
Radius | 0.14 ly |
Designations | HD 44179, [1] RAFGL 915 [1] |
The Red Rectangle Nebula, so called because of its red color and unique rectangular shape, is a protoplanetary nebula in the Monoceros constellation. Also known as HD 44179, the nebula was discovered in 1973 during a rocket flight associated with the AFCRL Infrared Sky Survey called Hi Star. The binary system at the center of the nebula was first discovered by Robert Grant Aitken in 1915.
High-resolution images of it in visible and near infrared light reveal a highly symmetric, compact bipolar nebula with X-shaped spikes which imply anisotropic dispersion of the circumstellar material. The central binary system is completely obscured, providing no direct light. [2] [3]
The Red Rectangle is known to be particularly rich in polycyclic aromatic hydrocarbons (PAHs). [4] [5] [6] The presence of such carbon-bearing macromolecules in the X-shaped nebular component, while the equatorial regions are known to contain silicate-rich dust grains and O-bearing molecules, [7] was interpreted as due to a change of the O/C abundance ratio of the primary star during its late evolution. [8] However, PAHs could also be formed as a result of the development of a central photodissociation region, a region in which a very active chemistry appears due to dissociation of stable molecules by the UV emission of the central stellar system. The Red Rectangle was the first nebula around an evolved star in which an equatorial disk in rotation was well identified (the existence of such disks has been demonstrated only in a few of these objects, only expansion is observed in most of them). [9] However, the disk absorbs the stellar light and is practically not seen in the beautiful optical image, which mainly represents a relatively diffuse outflow that is very probably formed of material extracted from the denser disk. [10] The distinct rungs suggest several episodes of increased ejection rate.
The Hubble Space Telescope has revealed a wealth of new features in the Red Rectangle that cannot be seen by ground-based telescopes looking through Earth's turbulent atmosphere. The origins of many of the features in this dying star, in particular its X-shaped image, still remain hidden or even outright mysterious. The presence of a conspicuous bipolar symmetry is usual in protoplanetary and planetary nebulae. Theorists, like Noam Soker, Vincent Icke , Adam Frank, and others, have shown that this axial symmetry can appear as a result of shocks due to interaction of different phases of the stellar winds (characteristic of the late stellar evolution), but its origin is still debated. [11] On the other hand, the X-like shape and the low velocity of the outflowing gas in the Red Rectangle are peculiar, probably because its origin (associated to a stable, extended disk) is different than for most protoplanetary nebulae.
Gomez's Hamburger, also known as IRAS 18059-3211, is believed to be a young star surrounded by a protoplanetary disk. It was initially identified as a planetary nebula, and its distance was estimated to be approximately 6500 light-years away from Earth. However, recent results suggest that this object is a young star surrounded by a protoplanetary disk, at a distance of about 900 light-years away.
Minkowski 2-9, abbreviated M2-9 is a planetary nebula that was discovered by Rudolph Minkowski in 1947. It is located about 2,100 light-years away from Earth in the direction of the constellation Ophiuchus. This bipolar nebula takes the peculiar form of twin lobes of material that emanate from a central star. Astronomers have dubbed this object as the Twin Jet Nebula because of the jets believed to cause the shape of the lobes. Its form also resembles the wings of a butterfly. The nebula was imaged by the Hubble Space Telescope in the 1990s.
A protoplanetary nebula or preplanetary nebula is an astronomical object which is at the short-lived episode during a star's rapid evolution between the late asymptotic giant branch (LAGB) phase and the subsequent planetary nebula (PN) phase. A PPN emits strongly in infrared radiation, and is a kind of reflection nebula. It is the second-from-the-last high-luminosity evolution phase in the life cycle of intermediate-mass stars.
A bipolar outflow comprises two continuous flows of gas from the poles of a star. Bipolar outflows may be associated with protostars, or with evolved post-AGB stars.
HD 100546, also known as KR Muscae, is a pre-main sequence star of spectral type B8 to A0 located 353 light-years from Earth in the southern constellation of Musca. The star is surrounded by a circumstellar disk from a distance of 0.2 to 4 AU, and again from 13 AU out to a few hundred AU, with evidence for a protoplanet forming at a distance of around 47 AU.
HD 141569 is an isolated Herbig Ae/Be star of spectral class A2Ve approximately 364 light-years away in the constellation of Libra. The primary star has two red dwarf companions at about nine arcseconds. In 1999, a protoplanetary disk was discovered around the star. A gap in the disk led to speculation about a possible extrasolar planet forming in the disk.
LL Pegasi is a Mira variable star surrounded by a pinwheel-shaped nebula, IRAS 23166+1655, thought to be a preplanetary nebula. It is a binary system that includes an extreme carbon star. The pair is hidden by the dust cloud ejected from the carbon star and is only visible in infrared light.
89 Herculis is a binary star system located about 4,700 light years away from the Sun in the northern constellation of Hercules. It is visible to the naked eye as a faint, fifth magnitude star. The system is moving closer to the Earth with a heliocentric radial velocity of −28.5 km/s.
HD 179821 or V1427 Aquilae is either a post-red supergiant yellow hypergiant or a post-AGB yellow supergiant star in the constellation of Aquila, surrounded by a detached dust shell. It is a semi-regular variable nearing the end of its life.
HDE 316285 is a blue supergiant star in the constellation Sagittarius. It is a candidate luminous blue variable and lies about 6,000 light years away in the direction of the Galactic Center.
HD 87643 is a B[e] class binary star embedded in a reflection nebula.
HD 65750, also known as V341 Carinae is a bright red giant star in the constellation Carina. It is surrounded by a prominent reflection nebula, known as IC 2220, nicknamed the Toby Jug Nebula.
IRAS 08544−4431 is a binary system surrounded by a dusty ring in the constellation of Vela. The system contains an RV Tauri variable star and a more massive but much less luminous companion.
SX Centauri is a variable star in the constellation Centaurus. An RV Tauri variable, its light curve alternates between deep and shallow minima, varying its apparent magnitude from 9.1 to 12.4. From the period-luminosity relationship, it is estimated to be around 1.6 kpc from Earth. Gaia Data Release 2 gives a parallax of 0.2175 mas, corresponding to distance of about 4,600 pc.
NGC 6778 is a planetary nebula (PN) located about 10,300 light years away from the Sun in the equatorial constellation of Aquila. It is positioned 5° to the SSW of the prominent star Delta Aquilae. This nebula was discovered by German astronomer Albert Marth during the period 1863–1865. English astronomer John Herschel may have mistakenly catalogued it as NGC 6785, as nothing can be found now at the coordinates he gave for it. In the New General Catalogue it was described as a "small, elongated, ill-defined disc".
HD 101584 is a suspected post-common envelope binary about 1,800 to 5,900 light-years distant in the constellation of Centaurus. The system is bright at optical wavelengths with an apparent visual magnitude of about 7. The primary is either a post-AGB star, but more likely a post-RGB star. The secondary is a red dwarf or possibly a low-luminosity white dwarf, which orbits the primary every 150-200 days. The system is surrounded by a slowly rotating circumbinary disk, probably with a face-on orientation towards the solar system and a size of about 150 astronomical units.
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.
HM Sagittae is a dusty-type symbiotic nova in the northern constellation of Sagitta. It was discovered by O. D. Dokuchaeva and colleagues in 1975 when it increased in brightness by six magnitudes. The object displays an emission line spectrum similar to a planetary nebula and was detected in the radio band in 1977. Unlike a classical nova, the optical brightness of this system did not rapidly decrease with time, although it showed some variation. It displays activity in every band of the electromagnetic spectrum from X-ray to radio.
HD 100453 is a binary star system which lies in the constellation Centaurus about 350 light years away from the Sun and is a member of the open cluster Scorpius–Centaurus association.
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.
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