Semi-regular variable

A semi-regular variable is a giant star or Supergéante of spectral Type intermediate or late which presents a periodicity marked in its variation of luminosity, accompanied or sometimes stopped by various irregularities. The periods are in a beach going of 20 until more than 2000 Jour S, while the form of the curved of light can be rather different and variable from one cycle to another. The amplitudes can go several hundredths until several magnitudes (usually 1-2 magnitudes in the filter V).

The variable semi-regular are classified in several sub-types:

  • SRA : Giants of the spectral type late (M, C, S or Me, This,) having a durable periodicity and generally a low amplitude, less than 2,5 magnitudes in the visible one. Z Aquarii is an example of this type. The amplitudes and the shape of the curves of light usually vary and the periods go from 35 to 1200 days. Many of these stars different from the variable from type Reflected only by lower amplitudes of luminosity.

  • SRB : Giants of the spectral type late (M, C, S or Me, This,) having a badly defined periodicity (average cycles going from 20 to 2300 days) or presenting alternations of periodic variations and slow variations irregular. Some can even sometimes completely stop varying during a certain time. RR Coronae Borealis and AF Cygni is examples of this behavior. One can however assign to each star of this type one average period. In some cases, two periods the simultaneous presence of variation or more is observed.

  • SRC : Supergéantes of the spectral type late (M, C, S or Me, This,) with amplitudes from approximately 1 magnitude and periods of variation going from 30 days to several thousands of days. Mu Cephei is a brilliant example of this type.

  • SRD : Giants or supergéantes of the spectral type F, G or K, having sometimes emission lines in their spectra. The amplitudes of variation of luminosity go from 0,1 to 4 magnitudes, and the periods lie between 30 and 1100 days. SX Herculis and SV Ursae Majoris is of the examples of this type. In M13, the amateur can see a dozen red variable stars magnitudes 11,95 to 12,25, with periods going 43 days (V24) to 97 days (V43).

See also

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