Cassiopeia

Cassiopeia is a constellation in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivalled beauty. Cassiopeia was one of the 48 constellations listed by the 2nd-century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today. It is easily recognizable due to its distinctive ‘M’ shape when in upper culmination but in higher northern locations when near lower culminations in spring and summer it has a ‘W’ shape, formed by five bright stars. It is bordered by Andromeda to the south, Perseus to the southeast, and Cepheus to the north. It is opposite the Big Dipper. The bright W asterism of the constellation is bright and compact, but the total area of Cassiopeia ranks it 25th in size out of the 88 modern constellations, covering 1.45% of the sky. It extends as far south as declination 46°, nearly to the Andromeda Galaxy, and to 77° at its northern edge. In northern locations above 34ºN latitude it is visible year-round and in the (sub)tropics it can be seen at its clearest from September to early November in its characteristic ‘M’ shape. Even in low southern latitudes below 25ºS it can be seen low in the North.

Johannes Hevelius’ Cassiopeia from Uranographia (1690)

The constellation is named after Cassiopeia, the queen of Ethiopia. Cassiopeia was the wife of Cepheus, King of Ethiopia and mother of Andromeda. Cepheus and Cassiopeia were placed next to each other among the stars, along with Andromeda. Cassiopeia was placed in the sky as a punishment for her boast that her daughter Andromeda was more beautiful than the Nereids or, alternatively, that she herself was more beautiful than the sea nymphs. As punishment, she was forced to wheel around the North Celestial Pole on her throne, spending half of her time clinging to it so she does not fall off, and Poseidon decreed that Andromeda should be bound to a rock as prey for the monster Cetus, who was ravishing the Ethiopian coast. Andromeda was then rescued by the hero Perseus, whom she later married.

Cassiopeia has been variously portrayed throughout her history as a constellation. In the 1600s, various Biblical figures were depicted in the stars of Cassiopeia. These included Bathsheba, Solomon’s mother; Deborah, an Old Testament prophet; and Mary Magdalene, a disciple of Jesus.

A figure called the ‘Tinted Hand’ also appeared in the stars of Cassiopeia in some Arab atlases. This is variously said to represent a woman’s hand dyed red with henna, as well as the bloodied hand of Muhammad’s daughter Fatima. The hand is made up of the stars α Cas, β Cas, γ Cas, δ Cas, ε Cas, and η Cas. The arm is made up of the stars α Per, γ Per, δ Per, ε Per, η Per, and ν Per. Another Arab constellation that incorporated the stars of Cassiopeia was the Camel. Its head was composed of Lambda, Kappa, Iota, and Phi Andromedae; its hump was Beta Cassiopeiae; its body was the rest of Cassiopeia, and the legs were composed of stars in Perseus and Andromeda.

In Persia, she was drawn by al-Sufi as a queen holding a staff with a crescent moon in her right hand, wearing a crown, as well as a two-humped camel.

In France, she was portrayed as having a marble throne and a palm leaf in her left hand, holding her robe in her right hand. This depiction was from Augustin Royer’s 1679 atlas.

In the ancient Celtic world Anu was the mother goddess and considered to be the mother of all the gods; the Tuatha de Danann. Other references say that she is the mother earth goddess or the Goddess of fertility. On the Cork Kerry border are two mountains called the Paps of Anu (pap is another word for breast.) On the top of each mountain are stone structures or cairns that when viewed from a distance make the two mountains look like a pair of breasts. Anu was known, in the Celtic World, by several similar names: Danu or Don being the most popular alternatives. She was a Mother-Goddess, the wife of the Sun God, Belenos, and considered to be the ancestor of all the Gods, the Tuatha dé Danann, who found themselves obliged to reside in the Otherworld when Miled brought the Celts to the British Isles. She still looks down on us from the night's sky where she appears as Llys Don, better known as the constellation of Cassiopeia.

In Chinese astronomy, the stars forming the constellation Cassiopeia are found among three areas: the Purple Forbidden enclosure (Zǐ Wēi Yuán), the Black Tortoise of the North (Běi Fāng Xuán Wǔ), and the White Tiger of the West (Xī Fāng Bái Hǔ). The Chinese astronomers saw several figures in what is modern-day Cassiopeia. Kappa, Eta, and Mu Cassopeiae formed a constellation called the Bridge of the Kings; when seen along with Alpha and Beta Cassiopeiae, they formed the great chariot Wang-Liang. The charioteer’s whip was represented by Gamma Cassiopeiae, sometimes called ‘Tsih,’ the Chinese word for ‘whip.’

Other cultures see a hand or moose antlers in the pattern. These include the Lapps, for whom the W of Cassiopeia forms an elk antler. The Chukchi of Siberia similarly saw the five main stars as five reindeer stags.

The people of the Marshall Islands saw Cassiopeia as part of a great porpoise constellation. The main stars of Cassiopeia make its tail, Andromeda and Triangulum form its body, and Aries makes its head. In Hawaii, Alpha, Beta, and Gamma Cassiopeiae were named. Alpha Cassiopeiae was called Poloahilani, Beta Cassiopeiae was called Polula, and Gamma Cassiopeiae was called Mulehu. The people of Pukapuka saw the figure of Cassiopeia as a distinct constellation called Na Taki-tolu-a-Mataliki.

[http://www.eaae-astronomy.org/newsletter/2012/n_21/EAAE-21.html]

Constellation of Cassiopeia

[http://www.davidmalin.com/fujii/source/Cas.html]

The five brightest stars of Cassiopeia make up the W shape;

Ultraviolet energy from the brilliant star Gamma Cassiopeiae, at top left, is eroding a nearby cloud of interstellar gas, limiting the birth of new stars. Gamma Cas emits most of its energy in the ultraviolet. If you include the UV with other wavelengths of light, Gamma Cas is roughly 65,000 times brighter than the Sun. It forms the middle point of W-shaped Cassiopeia, which is in the northeast on August evenings.

[https://stardate.org/radio/program/gamma-cassiopeia]

Gamma Cassiopeiae is the star at the center of the distinctive ‘W’ asterism in Cassiopeia. Although it is a fairly bright star with an apparent visual magnitude that varies from 1.6 to 3.0, it has no traditional Arabic or Latin name.

Gamma Cassiopeiae is a Be star, a variable star, and a binary. It is located at a distance of roughly 550 light-years from Earth.

Gamma Cassiopeiae is an eruptive variable star, whose apparent magnitude changes irregularly between +1.6 and +3.0. It is the prototype of the class of Gamma Cassiopeiae variable stars. In the late 1930s it underwent what is described as a shell episode and the brightness increased to above magnitude +2.0, then dropped rapidly to +3.4. It has since been gradually brightening back to around +2.2. At maximum intensity, γ Cassiopeiae outshines both α Cassiopeiae (magnitude +2.25) and β Cassiopeiae (magnitude +2.3).

Gamma Cassiopeiae is a rapidly spinning star with a projected rotational velocity of 472 km s−1, giving it a pronounced equatorial bulge. When combined with the star’s high luminosity, the result is the ejection of matter that forms a hot circumstellar disk of gas. The emissions and brightness variations are apparently caused by this ‘decretion’ disk.

The spectrum of this massive star matches a stellar classification of B0.5 IVe. A luminosity class of IV identifies it as a subgiant star that has reached a stage of its evolution where it is exhausting the supply of hydrogen in its core region and transforming into a giant star. The ‘e’ suffix is used for stars that show emission lines of hydrogen in the spectrum, caused in this case by the circumstellar disk. This places it among a category known as Be stars; in fact, the first such star ever to be so designated. It has 17 times the Sun’s mass and is radiating as much energy as 34,000 Suns. At this rate of emission, the star has reached the end of its life as a B-type main sequence star after a relatively brief 8 million years. The outer atmosphere has an intense effective temperature of 25,000 K, which is causing it to glow with a blue-white hue.

Gamma Cassiopeiae has two faint optical companions, listed in double star catalogues as components B and C. Gamma Cassiopeiae A, the bright primary, is itself a spectroscopic binary with an orbital period of about 203.5 days and an eccentricity alternately reported as 0.26 and ‘near zero.’ Star B is about 2 arc seconds distant and magnitude 11, and has a similar space velocity to the bright primary. The mass of the companion is believed to be about that of our Sun, but its nature is unclear. It has been proposed that it is a degenerate star or a hot helium star, but it seems unlikely that it is a normal star. Therefore, it is likely to be more evolved than the primary and to have transferred mass to it during an earlier stage of evolution. Component C is magnitude 13, nearly an arc second distant from B.

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

Alpha Cassiopeiae

[http://www.daviddarling.info/encyclopedia/S/Shedar.html]

Alpha Cassiopeiae is a second magnitude star in the constellation Cassiopeia, with the traditional name Schedar, sometimes spelled Shedir. The name, Schedar, was first encountered in the Alfonsine tables of the thirteenth century. The term comes from the Arabic word ‘şadr,’ meaning ‘breast,’ a word which is derived from its relative position in the heart of the mythological queen Cassiopeia. The estimated distance to the star is about 70 parsecs or 228 light years

Schedar’s apparent magnitude is marginally brighter or dimmer than Caph, the beta star in the constellation. Recent calculations produced a new measurement for both stars, 2.4107 for Schedar and 2.3579 for Caph, suggesting that Caph ranks as the brightest.

Schedar’s angular diameter is about 5.62 ± 0.06 milliarcseconds, which equates to roughly 0.393 AU or 42.3 solar radii. With the planet Mercury orbiting the Sun at approximately 0.4 AU, Schedar's photosphere extends to roughly half the mercurial orbit.

Schedar is an orange giant star whose spectral classification is K0IIIa, a stellar class that is notably cooler than the Sun. However, because the orange giant is nearing the final stages of its evolution, the photosphere has expanded substantially, yielding a bolometric luminosity that is approximately 676 times that of the sun.

Schedar has been sometimes classified as a variable star, but no variability has been detected since the 19th century. Also, three companions to the star have been listed in the Washington Double Star Catalog, but it seems that all of them are just line-of-sight optical components.

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

Beta Cassiopeiae is a Delta Scuti variable star in the constellation Cassiopeia, with the traditional name Caph, from the Arabic word ‘kaf,’ ‘palm’ (i.e. reaching from the Pleiades). It is located 54 light-years from Earth.

β Cassiopeiae is a yellow-white hued subgiant or giant of stellar class F2III-IV, with a surface temperature of 6,700 Kelvin. More than three times the size of and 28 times brighter than the Sun, Caph has an absolute magnitude of +1.16. It was once an A-type star with about double the Sun’s mass. It is now in the process of cooling and expanding to become a red giant. Its core is likely to have used up its hydrogen and is shrinking and heating, while its outer envelope of hydrogen is expanding and cooling. Stars do not spend much time in this state and are relatively uncommon. Caph’s corona is unusually weak.

β Cassiopeiae is a binary star, with a faint companion, which orbits it every 27 days. Little else is known about this companion.

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

Delta Cassiopeiae has the traditional name Ruchbah, which is derived from the Arabic word ‘rukbah’ meaning ‘knee.’ It is an eclipsing binary star system consisting of a pair of stars that orbit about each other over a period of 759 days. The combined apparent visual magnitude of the two stars is 2.68, making it readily observable with the naked eye. However, this magnitude varies between +2.68 mag and +2.74 as the stars pass in front of each other. Based on parallax measurements, this system is about 99.4 light-years (30.5 parsecs) from the Earth.

The primary member of the system has a stellar classification of A5III-IVv, with the luminosity class of IV indicating that it has exhausted the hydrogen at its core and has begun to evolve through the subgiant phase into a giant star. It has expanded to about 3.9 times the Sun’s radius. The lower case ‘v’ in the stellar class indicates that the spectrum shows signs of variation. The system has an estimated age of 600 million years.

An excess infrared emission has been observed at a wavelength of 60 μm, which suggests the presence of a circumstellar debris disk. This emission can be characterized by heat radiated from dust at a temperature of 85 K, which corresponds to an orbital radius of 88 Astronomical Units, or 88 times the distance of the Earth from the Sun. For comparison, the region of the remote Kuiper belt in the Solar System extends from 30–50 AU.

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

Epsilon Cassiopeiae is a star system in the constellation Cassiopeia. It has the traditional name Segin, which probably originates from an erroneous transcription of ‘Seginus,’ the traditional name for γ Boötis, which itself is of uncertain origin. With an apparent visual magnitude of 3.4, it is located at a distance of around 390- 430 light-years (120- 130 parsecs). The angular diameter is 0.43 milliarcseconds. At the estimated distance of this star, this yields a physical size of roughly 6 times the radius of the Sun.

ε Cassiopeiae is a giant star with a stellar classification of B3 III, indicating that it has exhausted the hydrogen at its core and entered a later evolutionary stages of its lifetime. The presence of emission lines in the spectrum indicates the presence of a circumstellar shell of gas that has been thrown off by the star. The outer atmosphere has an effective temperature of 15,174 K (14,901 °C; 26,854 °F), giving it the blue-white hue of a B-type star.

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

Just off the familiar W shape of the constellation Cassiopeia glimmers 4th-magnitude Rho Cassiopeiae- a yellow-white hypergiant star probably about to undergo a new episode of eruption, fading, and mass ejection (as of July 23, 2003).

Keep an eye on Cassiopeia- it contains a naked-eye star that may brighten and dim dramatically in the coming months. That was the message at a Tuesday press conference at the American Astronomical Society meeting in Seattle. Alex J. R. Lobel and Andrea Dupree reported observations of the active hypergiant star Rho Cassiopeiae, which is visible to the naked eye at magnitude 4.5. That it shines so brightly from 10,000 light-years away means that it must be huge. Rho Cas is about as hot as the Sun but roughly a million times more luminous, which makes it is so big that, if it replaced our Sun, its surface would lie beyond the orbit of Mars.

The star has had a chaotic recent past. In 1946 astronomers watched it fade to 6th magnitude and cool from 7,000° to 3,000° Kelvin, changing from spectral type F to M. Astronomers at the time speculated that it had undergone an enormous internal eruption that caused it to swell and cool, but they could not tell much else. The star eventually returned to normal. Then in 2000 astronomers caught Rho Cas acting up again. It brightened by 20 percent (0.2 magnitude), then dimmed by about two magnitudes while again cooling by more than 3,000° K.

This time astronomers were better prepared to study what was going on. The star turned out to be having the largest stellar mass ejection ever recorded. It ejected 50 Earths per day for 200 days. When the entire event was over, about 5 percent of a solar mass was gone- roughly a thousandth of Rho Cas’s mass.

It wouldn’t take many such ejections to have life-altering effects on the star. Its behavior may hold the answer to one of astronomy’s lingering questions- why are there no stars more luminous than a million Suns? “Maybe these mass losses constrain the luminosity,” suggests Dupree. If all hypergiants have episodic eruptions like Rho Cas, Lobel suggests, it could be why they can’t sustain superbright luminosities.

Clearly the star’s days are numbered. Rho Cas is in the very last stages of its evolution. It could go supernova in as little as 50,000 years.

It also seems to have an encore planned. The telltale spectral changes that it showed before its 2000 events have showed up again, only this time they are happening much faster. While Rho Cas isn’t expected to change much in coming days, “We are looking at months rather than years,” “We know this star did an amazing thing,” says Dupree. It may be poised to do so again.

[http://www.skyandtelescope.com/astronomy-news/a-star-prepares-to-blow-its-top/]

V509 Cassiopeiae

[https://jumk.de/astronomie/big-stars/v509-cassiopeiae.shtml]

HR 8752 Cas (HR 8752 Cassiopeiae). And now for something completely different, a huge massive star, one of the brightest in the Galaxy. Or not. The thing seems almost unknowable. The name comes from the Yale Bright Star Catalogue, though the ‘HR’ is from ‘Harvard Revised,’ curious to start with. ‘Bright Star’ is relative, as it shines at a fairly dim fifth magnitude (5.1) in, of course, Cassiopeia. An unstable irregular variable also known as V509 Cas, it changes between magnitudes 5.0 and 5.2. A monster class G (G4) hypergiant (or G0 supergiant), it seems to be a part of a huge collection of hot, luminous stars called Cepheus OB1 (never mind that the star is in Cassiopeia, as the expanding group sprawls all over). As such, it would lie 11,000 light years away.

Given 1.7 magnitudes of interstellar dust absorption and a temperature-guess of 6000 Kelvin, it then appears to radiate at a rate of 415,000 times that of the Sun, making it one of the most luminous stars of the Galaxy. Those figures translate into a star with a radius of three Astronomical Units- as big as the main asteroid belt- and an initial mass of 40 times that of the Sun. After ceasing core hydrogen fusion, it seems first to have evolved to the red supergiant state. A fierce wind then exposed the innards as it heated to become a ‘yellow hypergiant’ rather like Rho Cassiopeiae, the mass being cut in half, the star bouncing against the ‘yellow evolutionary void’ and unable to get much hotter. Consistently, HR 8752’s temperature has been increasing, starting at 4300 Kelvin in 1953 and going to 7200 K in the mid-nineties.

During the same time, the spectral class has flopped around from G4 to F8. Which gives us as bit of a problem, since if you can’t rely on temperature then you can’t trust the results that depend on it, so precision is lost. The mass loss, well over a millionth of a solar mass per year (100 million times the flow rate of the solar wind), has produced a huge shell that surrounds the star. A rotation velocity of 35 km/s (which is probably wrong) gives HR 8752 a rotation period of 2.5 years or under. That’s the standard.

However, all’s not well, as we have a problem with distance. The original Hipparcos satellite parallax reduction was unable to measure it. Recent re-evaluation of the data puts the distance of the star at 4500 light years, far closer, which gives a luminosity of ‘just’ 35,000 Suns and a mass of 15 solar, vastly less than earlier thought. On the other hand, the stated error is large. Plus, small parallaxes tend statistically to be too large, the star estimated to be too close. Moreover, stars in this mass range do not return from being red supergiants to become yellow supergiants. From all the information, the larger distance seems the more likely. But whatever the case, HR 8752 will almost certainly blow up as a huge supernova. And if nothing else, it humbles our attempts to learn about it and for that matter about others of its kind.

[http://stars.astro.illinois.edu/sow/hr8752.html]

The Shocking Behavior of a Speedy Star

Roguish runaway stars can have a big impact on their surroundings as they plunge through the Milky Way galaxy. Their high-speed encounters shock the galaxy, creating arcs, as seen in this newly released image from NASA’s Spitzer Space Telescope.

In this case, the speedster star is known as Kappa Cassiopeiae, or HD 2905 to astronomers. It is a massive, hot supergiant. But what really makes the star stand out in this image is the surrounding, streaky red glow of material in its path. Such structures are called bow shocks, and they can often be seen in front of the fastest, most massive stars in the galaxy.

Bow shocks form where the magnetic fields and wind of particles flowing off a star collide with the diffuse, and usually invisible, gas and dust that fill the space between stars. How these shocks light up tells astronomers about the conditions around the star and in space. Slow-moving stars like our sun have bow shocks that are nearly invisible at all wavelengths of light, but fast stars like Kappa Cassiopeiae create shocks that can be seen by Spitzer’s infrared detectors.

Incredibly, this shock is created about 4 light-years ahead of Kappa Cassiopeiae, showing what a sizable impact this star has on its surroundings. (This is about the same distance that we are from Proxima Centauri, the nearest star beyond the sun.)

The Kappa Cassiopeiae bow shock shows up as a vividly red color. The faint green features in this image result from carbon molecules, called polycyclic aromatic hydrocarbons, in dust clouds along the line of sight that are illuminated by starlight.

Delicate red filaments run through this infrared nebula, crossing the bow shock. Some astronomers have suggested these filaments may be tracing out features of the magnetic field that runs throughout our galaxy. Since magnetic fields are completely invisible themselves, we rely on chance encounters like this to reveal a little of their structure as they interact with the surrounding dust and gas.

Kappa Cassiopeiae is visible to the naked eye in the Cassiopeia constellation (but its bow shock only shows up in infrared light.)

For this Spitzer image, infrared light at wavelengths of 3.6 and 4.5 microns is rendered in blue, 8.0 microns in green, and 24 microns in red.

[http://www.spitzer.caltech.edu/images/5730-sig14-003-The-Shocking-Behavior-of-a-Speedy-Star]

The planetary system HD 7924

A team of astronomers using three ground-based telescopes has discovered two super-Earths around a nearby star known as HD 7924. HD 7924 is a 7th magnitude K-dwarf star, with a radius of around 78 percent that of the Sun. It is located in the constellation Cassiopeia, roughly 54 light-years away. Astronomers already knew that there was at least one exoplanet orbiting this star: they discovered HD 7924b- a super-Earth with a mass 9.2 times that of Earth and an orbital period of 5.4 days- in 2009. But now new observations have shown that there are at least three exoplanets orbiting HD 7924.

These additional exoplanets- HD 7924 c and d- have masses of 7.9 and 6.4 times that of Earth, and orbital periods of 15.3 and 24.5 days. The astronomers discovered them by detecting the wobble of HD 7924 as the planets orbited and pulled on the star gravitationally. The Automated Planet Finder (APF) and the Keck Observatory traced out the planets’ orbits over many years using the Doppler technique. The Automatic Photometric Telescope made crucial measurements of the HD 7924’s brightness to assure the validity of the planet discoveries.

“The new APF facility offers a way to speed up the planet search. Planets can be discovered and their orbits traced much more quickly because APF is a dedicated facility that robotically searches for planets every clear night,” said team member Lauren Weiss of the University of California, Berkeley.

“We initially used APF like a regular telescope, staying up all night searching star to star. But the idea of letting a computer take the graveyard shift was more appealing after months of little sleep. So we wrote software to replace ourselves with a robot,” added team leader Benjamin Fulton of the University of Hawaiʻi.

In honor of the donations of Gloria and Ken Levy that helped facilitate the construction of a spectrograph on the APF and supported Lauren Weiss, the astronomers has informally named the HD 7924 system the ‘Levy Planetary System.’

[http://www.sci-news.com/astronomy/science-super-earth-exoplanets-hd7924-02744.html]

Star HR 8832 (circled) lies just off the ‘W’ shape of the constellation Cassiopeia

HR 8832 (or HD 219134, or Gliese 892) is a main sequence star in the constellation of Cassiopeia. It is smaller and less luminous than our Sun, with a spectral class of K3V, which makes it an orange-red hued star. HR 8832 is relatively close to our system, with an estimated distance of 21.25 light years. This star is close to the limit of apparent magnitude that can still be seen by the unaided eye. The limit is considered to be magnitude 6 for most observers.

This star has a magnitude 9.4 companion at an angular separation of 106.6 arcseconds. The star is reported to host a rocky super-Earth, HD 219134 b, based on size (1.6 times the size of Earth), and density (6 grams per cubic cm). A further three exoplanets, two super-Earths and one Jovian world, have been deduced using Harps-N radial velocity data. Two more were discovered two months later.

[https://en.wikipedia.org/wiki/HR_8832]

[http://aladin.u-strasbg.fr/simbad-thumbnails/thumbnails6.html]

LS I +61 303 is a binary system harboring a compact object and a massive star (possibly a microquasar) that emits HE and VHE (High Energy and Very High Energy) gamma rays. It is only one of three known star systems that produce such energetic rays. The other two systems are PSR B1259-63 and LS 5039.

[https://en.wikipedia.org/wiki/LS_I_%2B61_303]

3C58: Pulsar Gives Insight on Ultra Dense Matter and Magnetic Fields

3C58 is the remnant of a supernova observed in the year 1181 by Chinese and Japanese astronomers. A long look by Chandra shows that the central pulsar- a rapidly rotating neutron star formed in the supernova event- is surrounded by a bright torus of X-ray emission. An X-ray jet erupts in both directions from the center of the torus, and extends over a distance of a few light years. Further out, an intricate web of X-ray loops can be seen.

These features are due to radiation from extremely high-energy particles moving in a magnetic field, and show a strong resemblance to the rings, jets and loops around the Crab pulsar. The 3C58 pulsar, the Crab pulsar, and a growing list of other pulsars provide dramatic proof that strong electromagnetic fields around rapidly rotating neutron stars are powerful generators of both high-energy particles and magnetic fields.

The pulsar in 3C58 can’t be seen directly in this image, but its presence has been deduced from an earlier Chandra discovery, and confirmation at radio wavelengths, of rapid (66 millisecond) pulsations. The present observations provide strong evidence that the surface of the 3C58 pulsar has cooled to a temperature of slightly less than a million degrees Celsius.

The relatively ‘cool’ surface temperature was a surprise to astrophysicists, since the standard theory for pulsar cooling predicts a much warmer surface at an age of only 830 years. The cooling of a pulsar is due to collisions between neutrons and other subatomic particles in its ultra dense interior where one teaspoonful of matter can weigh more than a billion tons. These collisions produce neutrinos that carry away energy as they escape from the star.

The speed of the cooling in 3C58 indicates that the interaction between neutrons and protons are not well understood at the extreme conditions in pulsars, or that an exotic form of subatomic matter is present.

Distance Estimate: 10,000 light years

[http://chandra.harvard.edu/photo/2004/3c58/]

Tycho G as seen by Hubble

Tycho G is the surviving binary companion star of the SN 1572 supernova event, often called ‘Tycho’s supernova,’ named after Tycho Brahe who observed the ‘new star’ in 1572. The star is located about 7500 light-years away in the constellation Cassiopeia. It is a subgiant, similar to our Sun in luminosity and color but more evolved. Tycho G is still close to the center of the supernova remnant and had triggered once the explosion of its binary companion white dwarf star by contributing mass to it. It is traveling at a rate of 136 km/s, which is more than four times faster than the mean velocity of other stars in its stellar neighbourhood:

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

Tycho’s Supernova Remnant: NASA’S Chandra Finds New Evidence on Origin of Supernovas

An arc of emission just found in the Tycho supernova remnant provides evidence for what triggered the original explosion. Astronomers think that a shock wave created the arc when a white dwarf exploded and blew material off the surface of a nearby companion star. Tycho belongs to a category of supernovas that are used to measure the expansion of the Universe.

This new image of Tycho’s supernova remnant, dubbed Tycho for short, contains striking new evidence for what triggered the original supernova explosion, as seen from Earth in 1572. Tycho was formed by a Type Ia supernova, a category of stellar explosion used in measuring astronomical distances because of their reliable brightness.

Low and medium energy X-rays in red and green show expanding debris from the supernova explosion. High energy X-rays in blue reveal the blast wave, a shell of extremely energetic electrons. Also shown in the lower left region of Tycho is a blue arc of X-ray emission. Several lines of evidence support the conclusion that this arc is due to a shock wave created when a white dwarf exploded and blew material off the surface of a nearby companion star (see accompanying illustration below). Previously, studies with optical telescopes have revealed a star within the remnant that is moving much more quickly than its neighbors, hinting that it could be the companion to the supernova that was given a kick by the explosion.

Other details of the arc support the idea that it was blasted away from the companion star. For example, the X-ray emission of the remnant shows an apparent "shadow" next to the arc, consistent with the blocking of debris from the explosion by the expanding cone of material stripped from the companion. This shadow is most obvious in very high energy X-rays showing iron debris.

These pieces of evidence support a popular scenario for triggering a Type Ia supernova, where a white dwarf pulls material from a ‘normal,’ or Sun-like, companion star until a thermonuclear explosion occurs. In the other main competing theory, a merger of two white dwarfs occurs, and in this case, no companion star or evidence for material blasted off a companion, should exist. Both scenarios may actually occur under different conditions, but the latest Chandra result from Tycho supports the former one.

The shape of the arc is different from any other feature seen in the remnant. Other features in the interior of the remnant include recently announced stripes, which have a different shape and are thought to be features in the outer blast wave caused by cosmic ray acceleration.

[http://chandra.harvard.edu/photo/2011/tycho2/index.html]

Another supernova remnant is Cassiopeia, and one of the most famous, is Cassiopeia A:

Recycling Cassiopeia A

For billions of years, massive stars in our Milky Way Galaxy have lived spectacular lives. Collapsing from vast cosmic clouds, their nuclear furnaces ignite and create heavy elements in their cores. After a few million years, the enriched material is blasted back into interstellar space where star formation begins anew. The expanding debris cloud known as Cassiopeia A is an example of this final phase of the stellar life cycle. Light from the explosion which created this supernova remnant was probably first seen in planet Earth's sky just over 300 years ago, although it took that light more than 10,000 years to reach us. In this gorgeous Hubble Space Telescope image of cooling filaments and knots in the Cas A remnant, light from specific elements has been color coded to help astronomers understand the recycling of our galaxy's star stuff. For instance, red regions are dominated by emission from sulfur atoms while blue shades correspond to oxygen. The area shown is about 10 light-years across.

[http://apod.nasa.gov/apod/ap030830.html]

Cassiopeia A: NASA’S Chandra Finds Superfluid in Neutron Star’s Core

Evidence for a bizarre state of matter- known as a superfluid- has been found in Cassiopeia A. Cassiopeia A (Cas A for short) is a supernova remnant located about 11,000 light years away from Earth.Chandra observations taken over a decade show significant cooling in the dense core left behind after the explosion.

This composite image shows a beautiful X-ray and optical view of Cassiopeia A (Cas A), a supernova remnant located in our Galaxy about 11,000 light years away. These are the remains of a massive star that exploded about 330 years ago, as measured in Earth’s time frame. X-rays from Chandra are shown in red, green and blue along with optical data from Hubble in gold.

At the center of the image is a neutron star, an ultra-dense star created by the supernova. Ten years of observations with Chandra have revealed a 4% decline in the temperature of this neutron star, an unexpectedly rapid cooling. Two new papers by independent research teams show that this cooling is likely caused by a neutron superfluid forming in its central regions, the first direct evidence for this bizarre state of matter in the core of a neutron star.

The Formation of a Superfluid in a Neutron Star

The inset shows an artist’s impression of the neutron star at the center of Cas A. The different colored layers in the cutout region show the crust (orange), the core (red), where densities are much higher, and the part of the core where the neutrons are thought to be in a superfluid state (inner red ball). The blue rays emanating from the center of the star represent the copious numbers of neutrinos- nearly massless, weakly interacting particles- that are created as the core temperature falls below a critical level and a neutron superfluid is formed, a process that began about 100 years ago as observed from Earth. These neutrinos escape from the star, taking energy with them and causing the star to cool much more rapidly.

Illustration of Cassiopeia A Neutron Star

This new research has allowed the teams to place the first observational constraints on a range of properties of superfluid material in neutron stars. The critical temperature was constrained to between one half a billion to just under a billion degrees Celsius. A wide region of the neutron star is expected to be forming a neutron superfluid as observed now, and to fully explain the rapid cooling, the protons in the neutron star must have formed a superfluid even earlier after the explosion. Because they are charged particles, the protons also form a superconductor.

Using a model that has been constrained by the Chandra observations, the future behavior of the neutron star has been predicted. The rapid cooling is expected to continue for a few decades and then it should slow down.

[http://chandra.harvard.edu/photo/2011/casa/]

Cassiopeia in the context of the Milky Way

[https://upload.wikimedia.org/wikipedia/commons/f/f9/Cassiopeia_in_Milky_Way.png]

The W in Cassiopeia

A familiar, zigzag, W pattern in northern constellation Cassiopeia is traced by five bright stars in this colorful and broad mosaic. Stretching about 15 degrees across rich starfields, the celestial scene includes dark clouds, bright nebulae, and star clusters along the Milky Way. In yellow-orange hues Cassiopeia’s alpha star Shedar is a standout though. The yellowish giant star is cooler than the Sun, over 40 times the solar diameter, and so luminous it shines brightly in Earth’s night from 230 light-years away. A massive, rapidly rotating star at the center of the W, bright Gamma Cas is about 550 light-years distant. Bluish Gamma Cas is much hotter than the Sun. Its intense, invisible ultraviolet radiation ionizes hydrogen atoms in nearby interstellar clouds to produce visible red H-alpha emission as the atoms recombine with electrons. Of course, night skygazers in the Alpha Centauri star system would also see the recognizable outline traced by Cassiopeia’s bright stars. But from their perspective a mere 4.3 light-years away they would see our Sun as a sixth bright star in Cassiopeia, extending the zigzag pattern just beyond the left edge of this frame.

[http://apod.nasa.gov/apod/ap160318.html]

Some of the star clusters and galaxies towards Cassiopeia are the following:

NGC 457

NGC 457 (also known as the Owl Cluster, the ET Cluster, or Caldwell 13) is an open star cluster in the constellation Cassiopeia. It was discovered by William Herschel in 1787, and lies over 7,900 light years away from the Sun. It has an estimated age of 21 million years. The cluster is sometimes referred by amateur astronomers as the Owl Cluster, Kachina Doll Cluster, the ET Cluster (due to its resemblance to the movie character) or the ‘Skiing Cluster.’ Two bright stars, magnitude 5 Phi-1 Cassiopeiae and magnitude 7 Phi-2 Cassiopeiae can be imagined as eyes. The cluster features a rich field of about 150 stars of magnitudes 12-15.

[https://en.wikipedia.org/wiki/NGC_457]

NGC 7789: Caroline’s Rose

Found among the rich starfields of the Milky Way toward the constellation Cassiopeia, star cluster NGC 7789 lies about 8,000 light-years away. A late 18th century deep sky discovery of astronomer Caroline Lucretia Herschel, the cluster is also known as Caroline’s Rose. Its suggestive appearance is created by the cluster’s nestled complex of stars and voids. Now estimated to be 1.6 billion years young, the galactic or open cluster of stars also shows its age. All the stars in the cluster were likely born at the same time, but the brighter and more massive ones have more rapidly exhausted the hydrogen fuel in their cores. These have evolved from main sequence stars like the Sun into the many red giant stars shown with a yellowish cast in this lovely color composite. Using measured color and brightness, astronomers can model the mass and hence the age of the cluster stars just starting to ‘turn off’ the main sequence and become red giants. Over 50 light-years across, Caroline’s Rose spans about half a degree (the angular size of the moon) near the center of the wide-field telescopic image.

[http://apod.nasa.gov/apod/ap131026.html]

Twin Dwarf Galaxies NGC 185 and NGC 147 in Cassiopeia

This pair of dwarf spheroidal (dSph) galaxies- slightly different than dwarf elliptical (dEs)- are satellites of M31, the Andromeda galaxy, with NGC 185 (left) at 2.08 million light years distant and NGC 147 (right) at a distance of 2.58 million light years. These two Andromeda satellites are now actually somewhat closer to the Milky Way than they are to Andromeda. They are probably gravitationally bound in a physical pair, with NGC 185 being the more interesting and diverse, having an active galactic nucleus and being classified as a Type 2 Seyfert Galaxy. NGC 147, however, is gas and dust free.

[http://hwilson.zenfolio.com/galaxies/h1f21d722#h1f21d722]

NGC 281: Living the High Life

NGC 281 is a relatively nearby cloud of gas and dust that lies high above the plane of the Milky Way galaxy. Its location makes NGC 281 a good target for astronomers who want to study ‘high-mass’ stars. High-mass stars are those that contain 8 times the Sun’s mass or more. These stars play an important role in galaxies, but are generally poorly understood because they are hard to observe.

High-mass stars are important because they are responsible for much of the energy pumped into our galaxy over its lifetime. Unfortunately, these stars are poorly understood because they are often found relatively far away and can be obscured by gas and dust. The star cluster NGC 281 is an exception to this rule. It is located about 9,200 light years from Earth and, remarkably, almost 1,000 light years above the plane of the Galaxy, giving astronomers a nearly unfettered view of the star formation within it.

This composite image of NGC 281 contains X-ray data from Chandra (purple) with infrared observations from Spitzer (red, green, blue). The high-mass stars in NGC 281 drive many aspects of their galactic environment through powerful winds flowing from their surfaces and intense radiation that heats surrounding gas, ‘boiling it away’ into interstellar space. This process results in the formation of large columns of gas and dust, as seen on the left side of the image. These structures likely contain newly forming stars. The eventual deaths of massive stars as supernovas will also seed the galaxy with material and energy.

NGC 281 is known informally as the ‘Pacman Nebula’ because of its appearance in optical images. In optical images the ‘mouth’ of the Pacman character appears dark because of obscuration by dust and gas, but in the infrared Spitzer image the dust in this region glows brightly.

[http://chandra.harvard.edu/photo/2011/ngc281/index.html]

NGC 7635: The Bubble Nebula

Blown by the wind from a massive star, this interstellar apparition has a surprisingly familiar shape. Cataloged as NGC 7635, it is also known simply as The Bubble Nebula. Although it looks delicate, the 7 light-year diameter bubble offers evidence of violent processes at work. Above and left of the Bubble’s center is a hot, O-type star, several hundred thousand times more luminous and around 45 times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula and associated cloud complex lie a mere 7,100 light-years away toward the boastful constellation Cassiopeia. This sharp, tantalizing view of the cosmic bubble is a composite of Hubble Space Telescope image data from 2016, released to celebrate the 26th anniversary of Hubble’s launch.

[http://apod.nasa.gov/apod/ap160422.html]

The Heart and Soul Nebulas

Is the heart and soul of our Galaxy located in Cassiopeia? Possibly not, but that is where two bright emission nebulas nicknamed Heart and Soul can be found. The Heart Nebula, visible in the above zoomable view on the right, has a shape reminiscent of a classical heart symbol. Both nebulas shine brightly in the red light of energized hydrogen. Several young open clusters of stars populate the image and are visible above in blue, including the nebula centers. Light takes about 6,000 years to reach us from these nebulas, which together span roughly 300 light years. Studies of stars and clusters like those found in the Heart and Soul Nebulas have focused on how massive stars form and how they affect their environment.

[http://apod.nasa.gov/apod/ap140211.html]

Melotte 15 in the Heart

Cosmic clouds form fantastic shapes in the central regions of emission nebula IC 1805. The clouds are sculpted by stellar winds and radiation from massive hot stars in the nebula's newborn star cluster, Melotte 15. About 1.5 million years young, the cluster stars are toward the right in this colorful skyscape, along with dark dust clouds in silhouette against glowing atomic gas. A composite of narrowband and broadband telescopic images, the view spans about 30 light-years and includes emission from ionized hydrogen, sulfur, and oxygen atoms mapped to green, red, and blue hues in the popular Hubble Palette. Wider field images reveal that IC 1805’s simpler, overall outline suggests its popular name- The Heart Nebula. IC 1805 is located about 7,500 light years away toward the boastful constellation Cassiopeia.

[http://apod.nasa.gov/apod/ap141018.html]

Comet Jacques, Heart and Soul

On July 13th, a good place to watch Comet Jacques was from Venus. Then, the recently discovered visitor (C/2014 E2) to the inner solar system passed within about 14.5 million kilometers of our sister planet. But the outbound comet will pass only 84 million kilometers from our fair planet on August 28 and is already a fine target for telescopes and binoculars. Two days ago Jacques’ greenish coma and straight and narrow ion tail were captured in this telescopic snapshot, a single 2 minute long exposure with a modified digital camera. The comet is flanked by IC 1805 and IC 1848, also known as Cassiopeia’s Heart and Soul Nebulae. If you're stuck on planet Earth this weekend you can hunt for Comet Jacques in evening skies, or spot a Venus, Jupiter, crescent Moon triangle before the dawn.

[http://apod.nasa.gov/apod/ap140822.html]

December 3-6, CAMS (Cameras for Allsky Meteor Surveillance) detected yet another meteor outburst with a radiant in Cassiopeia, this time from a Jupiter Family Comet, now called the December phi Cassiopeiids (DPC).

[http://cams.seti.org/maps.html]

The December Phi Cassiopeiids are a recently discovered early December meteor shower that radiates from Cassiopeia. Phi Cassiopeiids are very slow, with an entry velocity of approximately 16.7 kilometers per second. The shower’s parent body is a Jupiter family comet, though its specific identity is unknown.

If one were able to observe Earth’s Sun from Alpha Centauri, the closest star to the Solar System, it would appear in Cassiopeia as a yellow-white 0.5 magnitude star. The famous W of Cassiopeia would become a zig-zag pattern with the Sun at the leftmost end, closest to ε Cas.

[https://en.wikipedia.org/wiki/Cassiopeia_%28constellation%29]

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