A slow irregular variable (ascribed the
GCVS types L, LB and LC) is a
variable star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
that exhibit no or very poorly defined periodicity in their slowly changing light emissions. These stars have often been little-studied, and once more is learnt about them, they are reclassified into other categories such as
semiregular variables.
Nomenclature
Irregular variable stars were first given acronyms based on the letter "I": ''Ia'', ''Ib''. and ''Ic''.
[ These were later refined so that the I codes were used "nebular" or "rapidly irregular" variable stars such as T Tauri and Orion variables. The remaining irregular stars, cool slowly varying giants and supergiants of type Ib or Ic were reassigned to Lb and Lc.][ When the ]General Catalogue of Variable Stars
The General Catalogue of Variable Stars (GCVS) is a list of variable stars in the Milky Way Galaxy. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR, edited by and Pavel Parenago. Second a ...
standardised its acronyms to be all uppercase, the codes LB and LC were used.[
]
Type Lb
''Slow irregular variables of late spectral types ( K, M, C, S); as a rule, they are giants''[
The GCVS also claims to give this type to slow irregular red variables where the luminosity or spectral type is not known, although it also uses the type L for slow irregular red stars where the spectral type or luminosity is unclear. The K5 star CO Cygni is given as a representative example.][
]
Type Lc
''Irregular variable supergiants of late spectral types having amplitudes of about 1 mag in V''[
The M2 supergiant TZ Cassiopeiae is given as a representative example.][
]
List
Other irregular variables
There are a number of other types of variable stars lacking clearly detectable periods, and which are sometimes referred to as irregular variables:[
* γ Cassiopeiae variables, eruptive shell stars
* Orion variables, pre-main-sequence stars, including ]T Tauri star
T Tauri stars (TTS) are a class of variable stars that are less than about ten million years old. This class is named after the prototype, T Tauri, a young star in the Taurus Molecular Cloud, Taurus star-forming region. They are found near mo ...
s and YY Orionis stars
*Rapid irregular variables, possibly similar to Orion variables with shorter period
*Poorly-defined irregular variable stars, of unknown type
In addition, many types of eruptive or cataclysmic variable are highly unpredictable.[
]
References
External links
Classifying variable stars
- Astronomical Society of South Australia
Why observe variable stars
- British Astronomical Association
{{Variable star topics
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