Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Aquila |
Right ascension | 19h 18m 20.476s [1] |
Declination | +01° 47′ 59.62″ [1] |
Apparent magnitude (V) | 10.4 [2] – >23 [3] |
Characteristics | |
Spectral type | [WC4] [3] |
Astrometry | |
Radial velocity (Rv) | +80 [4] km/s |
Distance | 4,600 [4] pc |
Details | |
Mass | ~1 [5] M☉ |
Luminosity | 10,000 [3] L☉ |
Temperature | 5,000 – 95,000 [3] K |
Other designations | |
Database references | |
SIMBAD | data |
V605 Aquilae, in the constellation Aquila, is the variable central star of the planetary nebula Abell 58. It is a highly unusual hydrogen-deficient carbon-rich star.
V605 Aquilae was first recorded as a nova in 1919, but it turned out to be a very unusual variable. It was measured to be magnitude 10.4 at its peak. [2] Investigation of prior photographs showed that it was magnitude 15 or fainter until 1918, when it brightened to 12th magnitude. It stayed at 11th magnitude or brighter for over a year, before fading from sight. It then brightened to 12th magnitude in late 1921 and again in 1923, before disappearing. [6] The spectral type at the time of the outbursts was R0, a cool hydrogen-deficient carbon star similar to some R Coronae Borealis (RCB) stars. [4] [7]
V605 Aquilae was subsequently detected several times at magnitudes 18–20, but these are likely to have been detections only of a small knot of nebulosity surrounding the position of the star. Hubble images show that the star itself was fainter than magnitude 23, although the nebulosity was a bright irregular infrared object 2.5" across. It was suspected that the star was still luminous but largely hidden by the dense nebulosity. [3] Although the star could not be detected directly, scattered light showed a [WC4] spectral type, quite different from the spectrum at peak brightness. In 2013, the central star was detected at magnitude 20.2, with an estimated four magnitudes of extinction. The spectral type is now [WC4], a hydrogen-deficient, helium and carbon-rich object with strong emission lines. [4]
In 1921, the surface has been estimated to consist of 98% helium and 1% carbon, typical of an RCB star. By 2006, the abundances were measured as 55% helium, 45% carbon, and 5% oxygen, typical of a WC star. Both are very unusual, compared to the majority of stars that are mostly hydrogen. [3]
Starting around 1970, the temperature began to increase and is now over 90,000 K. It is widely believed to be a born-again star, a post-asymptotic-giant-branch star which experienced a very late thermal pulse and began to fuse again. [3] An alternative explanation is that the outburst was a nova from an oxygen-neon white dwarf. To explain difficulties with the nova theory, a merger has been proposed between a white dwarf and a normal companion star. [4]
V605 Aquilae is at the centre of a planetary nebula and is believed to be the source of the nebula. The visible planetary nebula is approximately spherical and far older than the 1919 outburst. A much smaller nebula originating from the outburst is non-spherical. The shape may be a disc plus a bipolar nebula or torus containing a dusty band. The band or disc almost entirely obscures the central star. Comparison of the angular size changes of the nebula and its radial velocities suggest a distance of 4,600 parsecs. [4]
A nova is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star, that slowly fades over several weeks or many months. Causes of the dramatic appearance of a nova vary, depending on the circumstances of the two progenitor stars. All observed novae involve a white dwarf in a close binary system. The main sub-classes of novae are classical novae, recurrent novae (RNe), and dwarf novae. They are all considered to be cataclysmic variable stars.
Sagitta is a dim but distinctive constellation in the northern sky. Its name is Latin for 'arrow', not to be confused with the significantly larger constellation Sagittarius 'the archer'. It was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations defined by the International Astronomical Union. Although it dates to antiquity, Sagitta has no star brighter than 3rd magnitude and has the third-smallest area of any constellation.
Eta Carinae, formerly known as Eta Argus, is a stellar system containing at least two stars with a combined luminosity greater than five million times that of the Sun, located around 7,500 light-years (2,300 parsecs) distant in the constellation Carina. Previously a 4th-magnitude star, it brightened in 1837 to become brighter than Rigel, marking the start of its so-called "Great Eruption". It became the second-brightest star in the sky between 11 and 14 March 1843 before fading well below naked eye visibility after 1856. In a smaller eruption, it reached 6th magnitude in 1892 before fading again. It has brightened consistently since about 1940, becoming brighter than magnitude 4.5 by 2014.
Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface enhancement of heavy elements, depletion of hydrogen, and strong stellar winds. The surface temperatures of known Wolf-Rayet stars range from 30,000 K to around 210,000 K, hotter than almost all other kinds of stars. They were previously called W-type stars referring to their spectral classification.
The Cat's Eye Nebula is a planetary nebula in the northern constellation of Draco, discovered by William Herschel on February 15, 1786. It was the first planetary nebula whose spectrum was investigated by the English amateur astronomer William Huggins, demonstrating that planetary nebulae were gaseous and not stellar in nature. Structurally, the object has had high-resolution images by the Hubble Space Telescope revealing knots, jets, bubbles and complex arcs, being illuminated by the central hot planetary nebula nucleus (PNN). It is a well-studied object that has been observed from radio to X-ray wavelengths.
A carbon star is typically an asymptotic giant branch star, a luminous red giant, whose atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds, giving the star a "sooty" atmosphere and a strikingly ruby red appearance. There are also some dwarf and supergiant carbon stars, with the more common giant stars sometimes being called classical carbon stars to distinguish them.
The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars late in their lives.
R Coronae Borealis is a low-mass yellow supergiant star in the constellation of Corona Borealis. It is the prototype of the R Cor Bor class of variable stars, which fade by several magnitudes at irregular intervals. R Coronae Borealis itself normally shines at approximately magnitude 6, just about visible to the naked eye, but at intervals of several months to many years fades to as faint as 15th magnitude. Over successive months it then gradually returns to its normal brightness, giving it the nickname "reverse nova", after the more common type of star which rapidly increases in brightness before fading.
RV Tauri variables are luminous variable stars that have distinctive light variations with alternating deep and shallow minima.
Sakurai's Object is a star in the constellation of Sagittarius. It is thought to have previously been a white dwarf that, as a result of a very late thermal pulse, swelled and became a red giant. It is located at the center of a planetary nebula and is believed to currently be in thermal instability and within its final shell helium flash phase.
An R Coronae Borealis variable is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation, and one irregular, unpredictably-sudden fading by 1 to 9 magnitudes. The prototype star R Coronae Borealis was discovered by the English amateur astronomer Edward Pigott in 1795, who first observed the enigmatic fadings of the star. Only about 150 RCB stars are currently known in our Galaxy while up to 1000 were expected, making this class a very rare kind of star.
FG Sagittae is a supergiant star in the constellation Sagitta at a distance of 4000 light-years. When first noted in 1943, it was identified to be a variable star, and it was found to be a hot, blue star of stellar spectral type B in 1955. Since then it has expanded and cooled, becoming a yellow G-type star by 1991, and then further cooling to become an orange K-type star. It started to pulsate when becoming an A-type star with a period of 15 days. This period later increased to over 100 days.
An extreme helium star, or a PV Telescopii Variable, is a low-mass supergiant that is almost devoid of hydrogen, the most common chemical element of the Universe. Since there are no known conditions where stars devoid of hydrogen can be formed from molecular clouds, it is theorized that they are the product of the mergers of helium-core and carbon-oxygen core white dwarfs.
WZ Sagittae is a cataclysmic dwarf nova star system in the constellation Sagitta. It consists of a white dwarf primary being orbited by a low mass companion. The white dwarf is about 0.85 solar masses while the companion is only 0.08 solar masses. This implies that the companion is a spectral class L2 star, although this has yet to be confirmed. The distance to this system has been determined by parallax, yielding a distance of 45.1 parsecs.
V445 Puppis was a nova in the constellation Puppis. It was discovered by Kazuyoshi Kanatsu of Matsue, Shimane, Japan, who recorded a peak magnitude of 8.6 on November 28, 2000. The nova was reported by Taichi Kato of Kyoto University in the International Astronomical Union circular 7552, issued on December 30, 2000. The location of this nova coincided with a magnitude 13.1 star that had been photographed in 1967. The proper motion of this star was measured as -4.7 mas/yr in right ascension and +6.4 mas/yr in declination, with a standard error of 4 mas/yr.
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.
CK Vulpeculae is considered to be the oldest reliably-documented nova. It consists of a compact central object surrounded by a bipolar nebula.
A hydrogen-deficient star is a type of star that has little or no hydrogen in its atmosphere. Hydrogen deficiency is unusual in a star, as hydrogen is typically the most common element in a stellar atmosphere. Despite being rare, there are a variety of star types that display a hydrogen deficiency.
DY Centauri is a variable star in the constellation Centaurus. From its brightness, it is estimated to be 7000 parsecs (23000 light-years) away from Earth.
V1370 Aquilae, also known as Nova Aquilae 1982, is a nova that appeared in the constellation Aquila during 1982. It was discovered by Minoru Honda of Kurashiki, Japan at 20:30 UT on 27 January 1982. At that time the Sun had moved just far enough from Aquila to allow the nova to be seen in the morning sky. Although it was discovered photographically, its apparent magnitude was 6–7, making it potentially visible to the naked eye under ideal conditions. A possible magnitude 20 progenitor was located on the Palomar Sky Survey prints. Spectra of the object were taken in February 1982 at Asiago Astrophysical Observatory, which confirmed that it is a nova.