HOME

TheInfoList



OR:

A slow irregular variable (ascribed the GCVS types L, LB and LC) is a variable
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
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 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 TZ Cassiopeaie (TZ Cas, HIP 117763, SAO 20912) is a variable star in the constellation Cassiopeia with an apparent magnitude of around +9 to +10. It is approximately 8,400 light-years away from Earth. The star is a red supergiant star wi ...
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 stars and
YY Orionis star An Orion variable is a variable star which exhibits irregular and eruptive variations in its luminosity and is typically associated with diffuse nebulae. It is thought that these are young stars which will later become regular, non-variable stars o ...
s *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 *