A long-period variable (LPV) is a type of pulsating cool giantvariable star with periods from a few days to a thousand or more, sometimes poorly defined, and sometimes irregular. Long-period variables have spectral class F and redwards, but most are red giants and AGB giants, meaning spectral class M, S or C. They are usually deep orange or red.
The following well defined variable star classes used to be counted into the LPV category, although in common usage often referring simply to Mira variables:
Mira variables, long rather regular pulsation periods in the range between 80 to 1000 days and grand light variations, from 2.5 magnitudes up to 11;
semiregular variables (SR), the periods in the same range as Miras, but lower amplitude and often irregularities that makes the period determination hard;
slow irregular variables (L), stars similar to the semiregulars, but whose period cannot be determined, because of the irregularity of the light change;
OGLE small amplitude red giants (OSARGs), forming several series having periods from a few days up to several hundred days and amplitudes of at most a few tenths of a magnitude.
The AAVSO LPV Section covers the Mira, SR, and L stars, but also RV Tauri variables, another type of large cool slowly varying star. This includes SRc and Lc stars which are respectively semi-regular and irregular cool supergiants. Recent researches have increasingly focused on the long period variables as only AGB and possibly red giant tip stars. The recently-classified OSARGs are by far the most numerous of these stars, comprising a high proportion of red giants.
^Soszynski; Udalski; Szymanski; Kubiak; Pietrzynski; Wyrzykowski; Szewczyk; Ulaczyk et al. (2009). "The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. IV. Long-Period Variables in the Large Magellanic Cloud". Acta Astronomica59 (239). arXiv:0910.1354. Bibcode:2009AcA....59..239S.|displayauthors= suggested (help)
^Masaki Takayama; Hideyuki Saio; Yoshifusa Ita (2013). "On the pulsation modes of OGLE small amplitude red giant variables in the LMC". arXiv:1303.7059 [astro-ph.SR].