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Thursday, May 3, 2018

Pyxis

[http://www.derekscope.co.uk/constellation-20th/pyxis/]



Pyxis is a small and faint constellation in the southern sky. Abbreviated from Pyxis Nautica, its name is Latin for a mariner’s compass (contrasting with Circinus, which represents a draftsman’s compasses). Pyxis was introduced by Nicolas Louis de Lacaille in the 18th century, and is counted among the 88 modern constellations. The constellation is located close to those forming the old constellation of the ship Argo Navis, and in the 19th century astronomer John Herschel suggested renaming Pyxis to Malus, the mast, but the suggestion was not followed.

Covering 220.8 square degrees and hence 0.535% of the sky, Pyxis ranks 65th of the 88 modern constellations by area. Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 52°N. It is most visible in the evening sky in February and March. It is bordered by Hydra to the north, Puppis to the west, Vela to the south, and Antlia to the east. In the equatorial coordinate system, the right ascension coordinates of the constellation lie between 8h 27.7m and 9h 27.6m, while the declination coordinates are between −17.41° and −37.29°.

Pyxis hovers over the mast of Argo on Chart XVIII of the Uranographia of Johann Bode (1801). Curling around it is a Bode invention, the now-obsolete Lochium Funis, the log and line.
[http://www.ianridpath.com/startales/pyxis.htm]

In ancient Chinese astronomy, Alpha, Beta and Gamma Pyxidis formed part of Tianmiao, a celestial temple honouring the ancestors of the emperor, along with stars from neighbouring Antlia.

The Ancient Greeks identified the four main stars of Pyxis as the mast of the great ship Argo Navis.

The French astronomer Nicolas Louis de Lacaille first described the constellation in French as la Boussole (the Marine Compass) in 1752, after he had observed and catalogued almost 10,000 southern stars during a two-year stay at the Cape of Good Hope. He devised fourteen new constellations in uncharted regions of the Southern Celestial Hemisphere not visible from Europe. Lacaille Latinized the name to Pixis [sic] Nautica on his 1763 chart.

German astronomer Johann Bode defined the constellation Lochium Funis, the Log and Line- a nautical device once used for measuring speed and distance travelled at sea- around Pyxis in his 1801 star atlas, but the depiction did not survive. In 1844 John Herschel attempted to resurrect the classical configuration of Argo Navis by renaming it Malus the Mast, a suggestion followed by Francis Baily, but Benjamin Gould restored Lacaille’s nomenclature.

[http://astropixels.com/constellations/charts/Pyx.html]

Constellations of Pyxis, Canis Major and the head of Hydra
[http://www.davidmalin.com/fujii/source/Pyx.html]

The three brightest stars of Pyxis- Alpha, Beta and Gamma Pyxidis- are in a rough line.

Alpha Pyxidis is a giant star. It has a stellar classification of B1.5III and is a Beta Cephei variable. This star has more than ten times the mass of the Sun and is more than six times the Sun’s radius. The surface temperature is 24,300 K and the star is about 10,000 times as luminous as the Sun. Stars such as this with more than 10 solar masses are expected to end their life by exploding as a supernova.
[https://en.wikipedia.org/wiki/Alpha_Pyxidis]

Beta Pyxidis is a double star. It has an apparent visual magnitude of 3.954, making it the second brightest star in that faint constellation. The star is an estimated 420 light-years (128 parsecs) from the Earth. The spectrum matches a bright giant or supergiant star of stellar classification G7Ib-II. The interferometer-measured angular diameter of this star is 2.05 ± 0.14 mas. At its estimated distance, this yields a physical size of about 28 times the radius of the Sun. The effective temperature of the star’s outer envelope is about 5,400 K, giving it the characteristic yellow hue of a G-type star.
[https://en.wikipedia.org/wiki/Beta_Pyxidis]

Gamma Pyxidis is a 4th magnitude star in the constellation Pyxis. It is classified as a giant star of composition similar to the Sun with an estimated diameter 3.7 times that of the Sun. It is located an estimated 207 light years from the Solar System. Gamma Pyxidis is moving through the Galaxy at a speed of 54.2 km/s relative to the Sun. Its projected Galactic orbit carries it between 21,300 and 30,700 light years from the center of the Galaxy.
[https://en.wikipedia.org/wiki/Gamma_Pyxidis]

T Pyx surrounded by the nova remnants of a previous outburst

T Pyxidis is a recurrent nova and nova remnant in the constellation Pyxis. It’s a binary star system and is estimated at about 4,783 parsecs (15,600 light-years) from Earth. It contains a Sun-like star and a white dwarf. Because of their close proximity and the larger mass of the white dwarf, the latter draws matter from the larger, less massive star. The influx of matter on the white dwarf’s surface causes periodic thermonuclear explosions to occur.

The usual apparent magnitude of this star system is 15.5, but there occurred eruptions with maximal apparent magnitude of about 7.0 in the years 1890, 1902, 1920, 1944, 1966 and 2011. Evidence seems to indicate that T Pyxidis may have increased in mass despite the nova eruptions, and is now close to the Chandrasekhar limit when it might explode as a supernova. When a white dwarf reaches this limit it will collapse under its own weight and cause a type 1a supernova.
[https://en.wikipedia.org/wiki/T_Pyxidis]

Pyxis lies in the plane of the Milky Way, although part of the eastern edge is dark, with material obscuring our galaxy arm there.

The Pyxis globular cluster is a 13.3 ± 1.3 billion year-old globular cluster situated around 130,000 light-years distant from Earth and around 133,000 light-years distant from the center of the Milky Way- a region not previously thought to contain globular clusters. Located in the galactic halo, it was noted to lie on the same plane as the Large Magellanic Cloud and the possibility has been raised that it might be an escaped object from that galaxy:

Gemini Multi-Object Spectrograph (GMOS-South) of the Pyxis field (left image), with the center of the cluster marked with a red star. A zoom of the pseudo color image of Pyxis observed with the Gemini South Adaptive Optics Imager (GSAOI) used with the Gemini Multi-conjugate adaptive optics System (GeMS) is shown at right. The field of view of GMOS is 5 x 5 arcminutes, 85 x 85 arcseconds for GeMS.

Researchers combine images from Gemini South’s wide-field adaptive optics system (GeMS/GSAOI) with data from the Hubble Space Telescope (HST) to determine the proper motion of a distant cluster of stars. The observations, the first to use ground-based adaptive optics to precisely measure the motion of a cluster at such a large distance, allowed astronomers to set a lower limit for the mass of our Milky Way while providing clues about the cluster’s origin.

A study of the proper motion (apparent motion in the sky due to an object’s motion around our galaxy) of several substructures across the Milky Way’s halo is underway at Gemini South. As part of this study the team used Adaptive Optics (AO) at Gemini South, along with data from HST, to focus on a distant cluster called Pyxis. The work allowed the team to set a lower limit for the Milky Way’s mass of 950 million solar masses. This value is consistent with most, but not all, previous determinations.

Pyxis, a densely packed collection of ancient stars, is one of the most distant examples of a globular clusters, dense clusters of stars which orbit our galaxy. The cluster is located some 130,000 light years away and is thought to be about 2 billion years younger than other globular clusters with the same ratio of heavier elements (metallicity). Together, these characteristics imply Pyxis did not form with other Milky Way clusters. Instead, it is likely that Pyxis was formed in a massive dwarf galaxy that was then accreted by the Milky Way. Thus, Pyxis has an extragalactic origin. However, the orbits of the known massive dwarf galaxies are inconsistent with the orbit of Pyxis, which is derived from the new proper motion measurements.
[https://www.gemini.edu/node/12662]

NGC 2818 is a planetary nebula that lies within a dim open cluster of magnitude 8.2. NGC 2818A is an open cluster that lies on line of sight with it:

Planetary Nebula NGC 2818 from Hubble

NGC 2818 is a beautiful planetary nebula, the gaseous shroud of a dying sun-like star. It could well offer a glimpse of the future that awaits our own Sun after spending another 5 billion years or so steadily using up hydrogen at its core, and then finally helium, as fuel for nuclear fusion. Curiously, NGC 2818 seems to lie within an open star cluster, NGC 2818A, that is some 10,000 light-years distant toward the southern constellation Pyxis (the Compass). At the distance of the star cluster, the nebula would be about 4 light-years across. But accurate velocity measurements show that the nebula’s own velocity is very different from the cluster's member stars. The result is strong evidence that NGC 2818 is only by chance found along the line of sight to the star cluster and so may not share the cluster’s distance or age. The Hubble image is a composite of exposures through narrow-band filters, presenting emission from nitrogen, hydrogen, and oxygen atoms in the nebula as red, green, and blue hues.
[http://apod.nasa.gov/apod/ap140713.html]

NGC 2613 is a spiral galaxy of magnitude 10.5 which appears spindle-shaped as it is almost edge-on to observers on Earth:

NGC 2613, a barred spiral galaxy in Pyxis

NGC 2613 is a barred spiral galaxy that lies about 66 million light-years away from Earth in the southern constellation of Pyxis (The Mariner’s Compass), while it is receding from us at 1660- 1676 kilometers per second. This galaxy is thought to resemble our own Milky Way. It has a nearby companion galaxy, designated ESO 495-G017.

NGC 2613 is an extremely massive galaxy that contains a deeply embedded active nucleus- that probably hosts a supermassive black hole- in a smooth bulge of stars from which the many tightly wound spiral arms emanate.

This rarely imaged starburst galaxy that we see nearly edge-on is known for a chaotic pattern of dark dust lanes superimposed upon the spiral arms, which contain stars, star clouds where new stars are being born, and interstellar gas and dust.

This image is based on data acquired with the 1.5-metre Danish telescope at ESO’s La Silla Observatory in Chile, through three filters.
[http://annesastronomynews.com/photo-gallery-ii/galaxies-clusters/ngc-2613-by-robert-gendler/]

Henize 2-10 is a dwarf galaxy which lies 30 million light-years away. It has a black hole of around a million solar masses at its center. Known as a starburst galaxy due to very high rates of star formation, it has a bluish color due to the huge numbers of young stars within it:

Henize 2-10, a Dwarf Starburst Galaxy

The combined observations from multiple telescopes of Henize 2-10, a dwarf starburst galaxy located about 30 million light years from Earth, has provided astronomers with a detailed new look at how galaxy and black hole formation may have occured in the early Universe. This image shows optical data from the Hubble Space Telescope in red, green and blue, X-ray data from NASA's Chandra X-ray Observatory in purple, and radio data from the National Radio Astronomy Observatory’s Very Large Array in yellow. A compact X-ray source at the center of the galaxy coincides with a radio source, giving evidence for an actively growing supermassive black hole with a mass of about one million times that of the sun.

Stars are forming in Henize 2-10 at a prodigious rate, giving the star clusters in this galaxy their blue appearance. This combination of a burst of star formation and a massive black hole is analogous to conditions in the early Universe. Since Henize 2-10 does not contain a significant bulge of stars in its center, these results show that supermassive black hole growth may precede the growth of bulges in galaxies. This differs from the relatively nearby Universe where the growth of galaxy bulges and supermassive black holes appears to occur in parallel.
[https://www.nasa.gov/mission_pages/chandra/multimedia/photo11-007.html#.V18qODUrRWA]

[https://en.wikipedia.org/wiki/Pyxis]




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