Large-amplitude variables near the Galactic Centre

We report here the results of a 4-yr K-band (2.2 mum) survey for large-ampl itude variable stars in a 24x24 arcmin(2) area centred on the Galactic Cent re. A total of 409 likely long-period variables (LPVs) were detected, for w hich positions, amplitudes, average magnitudes and periods were obtained wh enever possible. The surface density of LPVs is more than ten times greater than in the Sgr I Baade window at l=-1 degrees 37, b=-2 degrees 63. The limits of completeness arising from interstellar and circumstellar abso rption are discussed. Most of the area suffers interstellar extinction of 2 0 <A(V)< 40 mag. The shorter-period LPVs are less luminous than the longer- period ones and may be slightly under-represented in the data. Extremely he avy extinction (A(V)> 40 mag), which affects the probability of detecting v ariables, occurs in less than 25 per cent of the area. Almost all of the LPVs are Miras or OH/IR stars, with periods ranging from 150 d to about 800 d. K-band counterparts have been found for 59 per cent o f the 109 known OH sources in the field. The average period of the variable s found is 427 d, while that of the OH/IR stars is 524 d. For comparison, t he average period in the Sgr I window, which contains no known OH/IR stars, is 333 d and only two stars are detected with P > 600 d. The survey field also contains a number of long-period, large-amplitude variables that are n ot OH emitters.