Fourteen star systems have been found to have exoplanets, one of which- HR 8832-is thought to host seven planets. Cassiopeia A is a supernova remnant and the brightest extrasolar radio source in the sky at frequencies above 1 GHz. In 1572, Tycho Brahe's supernova flared brightly in Cassiopeia. The constellation hosts some of the most luminous stars known, including the yellow hypergiants Rho Cassiopeiae and V509 Cassiopeiae and white hypergiant 6 Cassiopeiae. In the (sub)tropics it can be seen at its clearest from September to early November, and at low southern, tropical, latitudes of less than 25°S it can be seen, seasonally, low in the North.Īt magnitude 2.2, Alpha Cassiopeiae, or Schedar, is generally the brightest star in Cassiopeia, though it is occasionally outshone by the variable Gamma Cassiopeiae, which has reached magnitude 1.6. It is easily recognizable due to its distinctive ' W' shape, formed by five bright stars.Ĭassiopeia is located in the northern sky and from latitudes above 34°N it is visible year-round. 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. Visible at latitudes between + 90° and − 20°.īest visible at 21:00 (9 p.m.) during the month of November.Ĭassiopeia ( listen) is a constellation in the northern sky named after the vain queen Cassiopeia, mother of Andromeda, in Greek mythology, who boasted about her unrivaled beauty. for the constellation also / ˌ k æ s i ˈ oʊ p i ə/ Cássiópeia Alternatively, the observed radiation may be interpreted as emitted by a compact object (more likely, a black hole) accreting from a residual disk or from a late-type dwarf in a close binary./ ˌ k æ s i ə ˈ p iː ə, - s i oʊ-/ Cássiopéia,Įsp. Such temperatures are consistent with the standard models of neutron star cooling. Among several possible interpretations, we favor a model of a strongly magnetized neutron star with magnetically confined hydrogen or helium polar caps (Tinfinitypc approximately 2.8 MK, Rpc approximately 1 km) on a cooler iron surface (Tinfinitys approximately 1.7 MK). An upper limit on the (gravitationally redshifted) surface temperature is Tinfinitys<1.9-2.3 MK, depending on the chemical composition of the surface and the star's radius. One cannot exclude, however, the possibility that the observed emission originates from hot spots on a cooler neutron star surface. Fits with the neutron star atmosphere models increase the radius and reduce the temperature, but these parameters are still substantially different from those expected for a young neutron star. The inferred radii are too small, and the temperatures too high, for the radiation to be interpreted as emitted from the whole surface of a uniformly heated neutron star. One can fit the spectrum equally well with a blackbody model with T=6-8 MK, R=0.2-0.5 km, and Lbol=&parl0 1.4-1.9&parr0 x1033 ergs s-1. The power-law index is higher, and the luminosity lower, than those observed from very young pulsars. The power-law fit yields the photon index gamma=2.6-4.1, and luminosity L(0.1-5.0 keV&parr0 =&parl0 2-60&parr0 x1034 ergs s-1 for d=3.4 kpc. Because of the small number of photons detected, different spectral models can fit the observed spectrum. The analysis of these data does not show statistically significant variability of the source. The central pointlike X-ray source of the Cassiopeia A supernova remnant was discovered in the Chandra first light observation and found later in the archival ROSAT and Einstein images.
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