Caelum constellation is located in the southern hemisphere. Its name is the Latin word for ‘chisel.’ Caelum is the eighth smallest constellation in the sky, occupying an area of only 125 square degrees. It lies in the first quadrant of the southern hemisphere (SQ1) and can be seen at latitudes between +40° and -90°. The neighboring constellations are Columba, Dorado, Eridanus, Horologium, Lepus, and Pictor.
[http://www.constellation-guide.com/constellation-list/caelum-constellation/]
Caelum shown as Caela Scalptoris on Chart XVIII of the Uranographia of Johann Bode, who added two scribing tools to the burin and échoppe described by Lacaille.
This small and insignificant constellation in the southern hemisphere, representing an engraver’s chisel, is one of the inventions of the 18th-century French astronomer Nicolas Louis de Lacaille. He introduced it on his map of the southern stars published in 1756, where he gave it the French name les Burins. On the second edition of the map in 1763 this was Latinized to Caelum Scalptorium. In 1844 the English astronomer John Herschel proposed shortening it to Caelum. Francis Baily adopted this suggestion in his British Association Catalogue of 1845, and it has been known as that ever since.
In the notes to the 1756 chart Lacaille said that the constellation represented two engraving tools, crossed and connected by a ribbon. One tool was a burin, a sharp-tipped cold chisel also known as a graver, while the other was an échoppe, a type of etching needle invented by the 17th-century French printmaker Jacques Callot. It is now just referred to as the chisel.
[http://www.ianridpath.com/startales/caelum.htm]
[http://space.about.com/od/starsplanetsgalaxies/ig/Constellations-Pictures/caelum.htm]
Constellations of Caelum and Columba
[http://www.davidmalin.com/fujii/source/Cae.html]
Alpha Caeli is a double star system in the constellation Caelum. Alpha Caeli A is an F-type main sequence star with a stellar classification of F2V and an apparent magnitude of +4.44. It has 1.48 times the mass of the Sun and 1.3 times the solar radius. The projected rotational velocity at the stellar equator is 47.8 km/s. It is suspected of being a Delta Scuti variable star.
The companion is a spectral class M0.5V red dwarf star with absolute magnitude 9.80. It is a UV Ceti variable star that undergoes random increases in luminosity. This star is currently separated from the primary by an angle of 6.6 arcseconds, which indicates an orbit with a semimajor axis whose expected value is 206 AU.
Alpha Caeli is approximately 65.7 light years from Earth and is an estimated 900 million years old. It is orbiting the Milky Way galaxy at an average distance of 8.006 kpc from the core and with an orbital eccentricity of 0.07. This orbit lies close to the galactic plane, and the system travels no more than 0.05 kpc above or below this plane. Alpha Caeli is probably a member of the Ursa Major moving group of stars that have similar kinematic properties and probably originated from the same star cluster.
[https://en.wikipedia.org/wiki/Alpha_Caeli]
Gamma Caeli in Caelum
[https://astronomypictureoftheday.wordpress.com/2010/02/17/gamma-caeli-in-caelum-constellation/]
Gamma1 Caeli is also double star, approximately 185 light years from Earth. The brighter component is an orange K-type giant with an apparent magnitude of +4.55. The companion is an eighth magnitude star located 3.1 arcseconds away.
[https://en.wikipedia.org/wiki/Gamma1_Caeli]
Beta Caeli is categorized as an F-type main sequence star with an apparent magnitude of +5.04. Beta Caeli is approximately 90.2 light years from Earth and slightly over six times brighter than the Sun.
[https://en.wikipedia.org/wiki/Beta_Caeli]
Delta Caeli is a blue-white B-type subgiant with an apparent magnitude of +5.07. It is approximately 711 light years from Earth.
[https://en.wikipedia.org/wiki/Delta_Caeli]
X Caeli, also known as Gamma2 Caeli, is a binary star in the constellation Caelum. It is approximately 334 light years from Earth. The primary component, X Caeli A, is a yellow-white F-type giant with a mean apparent magnitude of +6.32. It is classified as a Delta Scuti type variable star and its brightness varies from magnitude +6.28 to +6.39 with a period of 3.25 hours. The companion star, X Caeli B, has an apparent magnitude of +9.6 and is 0.886 arcseconds from the primary, and spectral type F2IV/V.
[https://en.wikipedia.org/wiki/X_Caeli]
RR Caeli is a double star, approximately 66 light years from Earth. It was first noted to be a high-proper motion star in 1955 by Jacob Luyten, and given the name LFT 349. Discovered to be an eclipsing binary in 1979, it has a baseline magnitude of 14.36, dimming markedly every 7.2 hours for an interval of around 10 minutes, due to the total eclipse of the brighter star by the fainter one. Its variability in brightness led to its being given the variable star designation RR Caeli in 1984.
This star system consists of a red dwarf of spectral type M6 and a white dwarf that orbit each other every seven hours; the former is 18% as massive as the Sun, while the latter has 44% of the Sun’s mass. The red dwarf is tidally locked with the white dwarf, meaning it displays the same side to the heavier star. The system is also a post-common-envelope binary, and the red dwarf star is transferring material onto the white dwarf. In approximately 9- 20 billion years, RR Caeli will likely become a cataclysmic variable star due to the period’s gradual shortening, leading to increasing rates of transfer of hydrogen to the surface of the white dwarf.
In 2012, analysis of slight variations in the observed light curve of the system showed that there was almost certainly a giant planet about four times as massive as Jupiter orbiting the pair of stars with a period of 11.9 years, and that there was evidence for a second possible substellar body further out as well. More observations of the light curve are likely to help confirm the presence of one or both planets.
[https://en.wikipedia.org/wiki/RR_Caeli]
Caelum is rather devoid of deep-sky objects, and contains no Messier objects. The only deep-sky object in Caelum to receive much attention is HE0450-2958, an unusual Seyfert galaxy. Originally, the jet’s host galaxy proved elusive to find, and this jet appeared to be emanating from nothing. Although it has been suggested that the object is an ejected supermassive black hole, the host is now agreed to be a small galaxy that is difficult to see due to light from the jet and a nearby starburst galaxy:
The Quasar without a Home: HE0450-2958
An international team of astronomers used two of the most powerful astronomical facilities available, the ESO Very Large Telescope (VLT) at Cerro Paranal and the Hubble Space Telescope (HST), to conduct a detailed study of 20 low redshift quasars. For 19 of them, they found, as expected, that these super massive black holes are surrounded by a host galaxy. But when they studied the bright quasar HE0450-2958, located some 5 billion light-years away, they couldn’t find evidence for an encircling galaxy. This, the astronomers suggest, may indicate a rare case of collision between a seemingly normal spiral galaxy and a much more exotic object harbouring a very massive black hole.
With masses up to hundreds of millions that of the Sun, ‘super massive’ black holes are the most tantalizing objects known. Hiding in the centre of most large galaxies, including our own Milky Way, they sometimes manifest themselves by devouring matter they engulf from their surroundings. Shining up to the largest distances, they are then called ‘quasars’ or ‘QSOs’ (for ‘quasi-stellar objects’), as they had initially been confused with stars.
Decades of observations of quasars have suggested that they are always associated with massive host galaxies. However, observing the host galaxy of a quasar is a challenging work, because the quasar is radiating so energetically that its host galaxy is hard to detect in the flare.
To overcome this problem, the astronomers devised a new and highly efficient strategy. Using ESO’s VLT for spectroscopy and HST for imagery, they observed their quasars at the same time as a reference star. Simultaneous observation of a star allowed them to measure at best the shape of the quasar point source on spectra and images, and further to separate the quasar light from the other contribution, i.e. from the underlying galaxy itself. This very powerful image and spectra sharpening method (‘MCS deconvolution’) was applied to these data in order to detect the finest details of the host galaxy.
Using this efficient technique, the astronomers could detect a host galaxy for all but one of the quasars they studied. No stellar environment was found for HE0450-2958, suggesting that if any host galaxy exists, it must either have a luminosity at least six times fainter than expected a priori from the quasar observed luminosity, or a radius smaller than about 300 light-years. Typical radii for quasar host galaxies range between 6,000 and 50,000 light-years, i.e. they are at least 20 to 170 times larger.
Instead, the astronomers detected just besides the quasar a bright cloud of about 2,500 light-years in size, which they baptized ‘the blob.’ The VLT observations show this cloud to be composed only of gas ionised by the intense radiation coming from the quasar. It is probably the gas of this cloud which is feeding the supermassive black hole, allowing it to become a quasar.
A strongly perturbed galaxy, showing all signs of a recent collision, is also seen on the HST images 2 arcseconds away (corresponding to about 50,000 light-years), with the VLT spectra showing it to be presently in a state where it forms stars at a frantic rate.
“The absence of a massive host galaxy, combined with the existence of the blob and the star-forming galaxy, lead us to believe that we have uncovered a really exotic quasar,” says team member Frédéric Courbin. “There is little doubt that a burst in the formation of stars in the companion galaxy and the quasar itself have been ignited by a collision that must haven taken place about 100 million years ago. What happened to the putative quasar host remains unknown.”
HE0450-2958 constitutes a challenging case of interpretation. The astronomers propose several possible explanations that will need to be further investigated and confronted. Has the host galaxy been completely disrupted as a result of the collision? It is hard to imagine how that could happen. Has an isolated black hole captured gas while crossing the disc of a spiral galaxy? This would require very special conditions and would probably not have caused such a tremendous perturbation as is observed in the neighbouring galaxy. Another intriguing hypothesis is that the galaxy harbouring the black hole was almost exclusively made of dark matter.
[https://www.eso.org/public/usa/news/eso0529/]
[https://en.wikipedia.org/wiki/Caelum]
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