RR Lyrae variable
Information about RR Lyrae variable
RR Lyrae variables are variable stars often used as standard candles.
RR Lyrae are pulsating Horizontal branch stars, with a mass of around half the Sun's. RR Lyrae stars shed mass prior to becoming RR Lyrae and consequently, RR Lyrae were once stars with similar or slightly less mass than the sun, around 0.8 solar masses. They pulse in a manner similar to Cepheid variables, but some important differences exist.
RR Lyrae are old, relatively low mass stars. Therefore, they are much more common than Cepheids, but less luminous. The average absolute magnitude of an RR Lyrae is 0.75, only 40 or 50 times brighter than our Sun. Their period is shorter, typically less than one day, and sometimes down to eight or nine hours.
There are three main types of RR Lyrae stars:
This type of variable is named after the prototype, the variable RR in the Lyra constellation.
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RR Lyrae are pulsating Horizontal branch stars, with a mass of around half the Sun's. RR Lyrae stars shed mass prior to becoming RR Lyrae and consequently, RR Lyrae were once stars with similar or slightly less mass than the sun, around 0.8 solar masses. They pulse in a manner similar to Cepheid variables, but some important differences exist.
RR Lyrae are old, relatively low mass stars. Therefore, they are much more common than Cepheids, but less luminous. The average absolute magnitude of an RR Lyrae is 0.75, only 40 or 50 times brighter than our Sun. Their period is shorter, typically less than one day, and sometimes down to eight or nine hours.
There are three main types of RR Lyrae stars:
- RRab
- RRc, which are shorter periods.
- RRd, which are double-mode pulsators.
This type of variable is named after the prototype, the variable RR in the Lyra constellation.
See also
Weblinks
- APOD four-frame animation of RR Lyrae variables in globular cluster M3
- Animation of RR Lyrae-Variables in globular cluster M15
- RR Lyrae stars
Variable Star
Author Robert A. Heinlein & Spider Robinson
Cover artist Stephan Martiniere
Country United States
Language English
Genre(s) Science fiction
Publisher Tor Books
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Author Robert A. Heinlein & Spider Robinson
Cover artist Stephan Martiniere
Country United States
Language English
Genre(s) Science fiction
Publisher Tor Books
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A standard candle is an astronomical object that has a known luminosity. Several important methods of deriving distances in extragalactic astronomy and cosmology are based on standard candles.
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The horizontal branch (HB) is a stage of stellar evolution which immediately follows the red giant branch in stars whose masses are similar to the Sun's. Horizontal branch stars are powered by helium fusion in the core (via the triple-alpha reaction) and by hydrogen fusion
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The Sun
Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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A Cepheid variable or Cepheid is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute luminosity.
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In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. It allows the overall brightnesses of objects to be compared without regard to distance.
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The Sun
Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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- For the unit of luminosity see standard candle
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globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers.
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A galaxy (from the Greek root γαλαξίας, meaning "milky", a reference to our own Milky Way) is a massive, gravitationally bound system consisting of stars, an interstellar medium of gas and dust, and dark matter.
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Lyra
Click for larger image
List of stars in Lyra
Abbreviation: Lyr
Genitive: Lyrae
Symbology: the Lyre
Right ascension: 19 h
Declination: +40
Area: 286 sq. deg.
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Click for larger image
List of stars in Lyra
Abbreviation: Lyr
Genitive: Lyrae
Symbology: the Lyre
Right ascension: 19 h
Declination: +40
Area: 286 sq. deg.
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RR Lyrae is a variable star in the Lyra constellation. It is the prototype of the RR Lyrae variables star class. It has a period of about 13 hours, and oscillates between apparent magnitudes 7 and 8.
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A W Virginis variable is a variable star similar to a Cepheid variable. However, using the formula for W Virginis variables to calculate distance of a Cepheid variable will yield a value that is too small, a mistake that Edwin Hubble made while observing M31.
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