Long period variable survey in NGC 6822

Context. The star-formation history of the intermediate-age population of the Local Group dwarf irregular galaxy NGC 6822 may have been influenced by the often discussed interaction with its HI cloud that might have produced the present polar-ring structure.
Aims: We investigate the period distribution of the Mira variables in the central region and the spheroid of NGC 6822.
Methods: We use the new wide-field near-infrared imager CPAPIR to acquire K_s images of a 32' × 32' area, which includes a good part of the eastern spheroid of NGC 6822.
Results: Periods could be determined for 45 cyclic and semi-regular variables brighter than < K > = 17. The vast majority of the variables have ages between 1 and 3 Gyr.
Conclusions: The period distribution of the long period variables may reflect the proposed interaction with the HI cloud that produces the polar ring.