Editing Semiregular variable star (section)

==Classification==
The semiregular variable stars have been sub-divided into four categories for many decades, with a fifth related group defined more recently.  The original definitions of the four main groups were formalised in 1958 at the tenth general assembly of the [[International Astronomical Union]] (IAU).  The [[General Catalogue of Variable Stars]] (GCVS) has updated the definitions with some additional information and provided newer reference stars where old examples such as [[S Vulpeculae|S Vul]] have been re-classified.

{| class="wikitable"
|+Semiregular variable subtypes
|- style="vertical-align: top;"
! Subtype<ref name=IAU/> !! IAU definition<ref name=IAU/> !! GCVS code<ref name=GCVS/> !! GCVS definition<ref name=GCVS/> !! Standard<br/>stars
|- style="vertical-align: top;"
| SRa
|| <small>''semi-regular variable giants'' of ''late'' spectral classes (M, C and S), which retain periodicity with comparative stability  and possess, as a rule, small (less than 2<sup>m</sup>.5) light-variation amplitudes. Amplitudes and forms of light curves are usually liable to strong variations from period to period.  Many of these stars differ from Mira Ceti type stars only owing to the smaller amplitude of light variation.</small>
|| SRA
|| <small>Semiregular late-type (M, C, S or Me, Ce, Se) giants displaying persistent periodicity and usually small (<2.5 mag in V) light amplitudes. Amplitudes and light-curve shapes generally vary and periods are in the range of 35–1200 days. Many of these stars differ from Miras only by showing smaller light amplitudes</small>
|| [[Z Aquarii|Z Aqr]]<ref name=IAU/><ref name=GCVS/>
|- style="vertical-align: top;"
| SRb
|| <small>''semi-regular variable giants'' of ''late'' spectral classes (M, C and S) with a poorly expressed periodicity, i.e. with a different duration of individual cycles (which leads to the impossibility of predicting the epochs of maximum and minimum brightness), or with the replacement of periodical changes by slow irregular variations, or even by the constancy of brightness. Some of them are characterised by a certain mean value of the period, given in the catalogue.</small>
|| SRB
|| <small>Semiregular late-type (M, C, S or Me, Ce, Se) giants with poorly defined periodicity (mean cycles in the range of 20 to 2300 days) or with alternating intervals of periodic and slow irregular changes, and even with light constancy intervals. Every star of this type may usually be assigned a certain mean period (cycle), which is the value given in the Catalogue. In a number of cases, the simultaneous presence of two or more periods of light variation is observed</small>
|| [[AF Cygni|AF Cyg]]<ref name=IAU/><ref name=GCVS/><br/>{{nowrap|[[RR Coronae Borealis|RR CrB]]}}<ref name=IAU/><ref name=GCVS/>
|- style="vertical-align: top;"
| SRc
|| <small>''semi-regular variable super-giants'' of ''late'' spectral classes</small>
|| SRC
|| <small>Spectral-type (M, C, S or Me, Ce, Se) supergiants with amplitudes of about 1 mag and periods of light variation from 30 days to several thousand days.</small>
|| [[Mu Cephei|μ Cep]]<ref name=IAU/><ref name=GCVS/><br/>[[RW Cygni|RW Cyg]]<ref name=IAU/>
|- style="vertical-align: top;"
| SRd
|| <small>''semi-regular variable giants and super-giants'' belonging to spectral classes F, G, K</small>
|| SRD
|| <small>Semiregular variable giants and supergiants of F, G, or K spectral types, sometimes with emission lines in their spectra. Amplitudes of light variation are in the range from 0.1 to 4 mag, and the range of periods is from 30 to 1100 days</small>
|| [[S Vulpeculae|S Vul]]<ref name=IAU/><br/>[[UU Herculis|UU Her]]<ref name=IAU/><br/>[[AG Aurigae|AG Aur]]<ref name=IAU/><br/>[[SX Herculis|SX Her]]<ref name=GCVS/><br/>[[SV Ursae Majoris|SV UMa]]<ref name=GCVS/>
|- style="vertical-align: top;"
||
||
|| SRS
|| <small>Semiregular pulsating red giants with short period (several days to a month), probably high-overtone pulsators</small>
|| [[AU Arietis|AU Ari]]<ref name=GCVS/>
|}