Irregular and Semi-Regular Variable Stars

Irregular Variables Facts

• Irregular Variables are stars that do not vary in a pattern.

What are Irregular Variable Star?

An Irregular Variable Star is a star that differs in brightness with no discernable pattern. They can be broken down into one of two subgroups. The first group are known as Eruptive, the second, Pulsating are also referred to as Slow Irregular.

• Eruptive - This where the star brightens due to an eruption such as a solar flare.
  
• Group 1a - Spectral types O to A (hottest)
• Group 1b - Spectral types F to M (coldest)
• Group IN - Irregular Nebulous variables, these stars are found in star-forming regions. Their brightness can increase and decrease in a matter of days, up to 10 days. They can be further broken down into smaller groups.
  • INA - Orion Variables of early spectral types (B-A or Ae) example is XY Persei
  • INB - Orion Variables of late spectral types (F-M or Fe-Me) IX Ophiuchi
  • INT -> T-Tauri Stars
  • INT(YY) -> YY Orionis Stars
  • IS - Rapid variability that can occur in hours or days. These stars can change their magnitude from 0.5 to a full magnitude.
  • ISA - Rapid irregular variables associated with early spectral types (B-A or Ae) Example include UX Orionis
  • ISB - Rapid irregular variables associated with late spectral types (F-M and Fe-Me)

What are Slow Irregular Variable Star

• Pulsating - This is where the star expands and contracts. These tend to occur in older, larger stars, typically giants or supergiants. They are broken into two main groups
  • Lb - giant stars - Examples include Psi Virginis
  • Lc - Supergiant Stars - Examples include Antares

Related Pages of Interest :-

• Cepheid Variables
• Delta Scuti Variable
• Mira Variable Stars
• Semi-Regular Variable Star

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