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R Aquarii is a symbiotic star believed to contain a white dwarf and a Mira-type variable in a binary system. The orbital period is approximately 44 years. [5] The main Mira-type star is a red giant , and varies in brightness by a factor of several hundred and with a period of slightly more than a year; this variability was discovered ...
A star is a luminous spheroid of plasma held together by self-gravity. [1] . The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light.
- Discovery and Recognition
- Classification
- Distribution
- Properties
- Period-Luminosity Relationships
- Recent Developments
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In surveys of globular clusters, these "cluster-type" variables were being rapidly identified in the mid-1890s, especially by E. C. Pickering. Probably the first star definitely of RR Lyrae type found outside a cluster was U Leporis, discovered by J. Kapteyn in 1890. The prototype star RR Lyrae was discovered prior to 1899 by Williamina Fleming, an...
The RR Lyrae stars are conventionally divided into three main types, following classification by S.I. Baileybased on the shape of the stars' brightness curves: 1. RRab variables are the most common, making up 91% of all observed RR Lyrae, and display the steep rises in brightness typical of RR Lyrae 2. RRc are less common, making up 9% of observed ...
RR Lyrae stars were formerly called "cluster variables" because of their strong (but not exclusive) association with globular clusters; conversely, over 80% of all variables known in globular clusters are RR Lyraes. RR Lyrae stars are found at all galactic latitudes, as opposed to classical Cepheids, which are strongly associated with the galactic ...
RR Lyrae stars pulse in a manner similar to Cepheid variables, but the nature and histories of these stars is thought to be rather different. Like all variables on the Cepheid instability strip, pulsations are caused by the κ-mechanism, when the opacity of ionised helium varies with its temperature. RR Lyraes are old, relatively low mass, Populatio...
Unlike Cepheid variables, RR Lyrae variables do not follow a strict period-luminosity relationship at visual wavelengths, although they do in the infrared K band. They are normally analysed using a period-colour-relationship, for example using a Wesenheit function. In this way, they can be used as standard candles for distance measurements although...
The Hubble Space Telescope has identified several RR Lyrae candidates in globular clusters of the Andromeda Galaxyand has measured the distance to the prototype star RR Lyrae. The Kepler space telescope provided accurate photometriccoverage of a single field at regular intervals over an extended period. 37 known RR Lyrae variables lie within the Ke...
APOD M3: Inconstant Star Clusterfour-frame animation of RR Lyrae variables in globular cluster M3Proton–proton chain. Logarithm of the relative energy output (ε) of proton–proton (PP), CNO and Triple-α fusion processes at different temperatures (T). The dashed line shows the combined energy generation of the PP and CNO processes within a star. At the Sun's core temperature of 15.5 million K the PP process is dominant.
Betelgeuse is a red supergiant star in the constellation of Orion. It is usually the tenth-brightest star in the night sky and, after Rigel, the second-brightest in its constellation.
Scorpius–Centaurus association. The Scorpius–Centaurus association (sometimes called Sco–Cen or Sco OB2) is the nearest OB association to the Sun. This stellar association is composed of three subgroups (Upper Scorpius, Upper Centaurus–Lupus, and Lower Centaurus–Crux) and its distance is about 130 parsecs or 420 light-years. [1]
Pulsar planets are planets that are orbiting pulsars. The first such planets to be discovered were around a millisecond pulsar in 1992 and were the first extrasolar planets to be confirmed as discovered. Pulsars are extremely precise clocks and even small planets can create detectable variations in pulsar traits; the smallest known exoplanet is ...
