Period–magnitude relations for M giants in Baade's Window NGC 6522

A large and complete sample of stars with   K < 9.75  in the NGC 6522 Baade's Window towards the Galactic bulge is examined using light curves extracted from MACHO and IJK photometry from DENIS.
The improved statistics resulting from a sample of over 1000 variables allow all four of the sequences A, B, C and D in the   K _S   , log  P diagram of the Large Magellanic Cloud to be seen in the Galactic bulge. The bulge sequences, however, show some differences from those in the Magellanic Clouds, possibly due to the effects of higher metallicity. These sequences may have value as distance indicators.
A new diagram of the frequency of late-type variables at a given amplitude is derived and compared with the old one from Payne-Gaposchkin. The catalogued semiregular variables of the solar neighbourhood are found to be a subset of the total of semiregulars, biased towards large amplitude.