Large Amplitude variables near the Galactic Centre

I.S. Glass1, S. Matsumoto2, B.S. Carter3 and K. Sekiguchi4

1South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa,2Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181, Japan, 3Carter Observatory, PO Box 2909, Wellington, New Zealand, 4Subaru Telescope, NAOJ, 650 North A'ohoku Place, Hilo, HI 96720, USA

Paper: MNRAS, in press



We report here the results of a four-year K-band (2.2 micron ) survey for large-amplitude variable stars in a 24 * 24 arcmin2 area centered on the Galactic Centre. A total of 409 likely long-period variables (LPVs) were detected, for which positions, amplitudes, average magnitudes and periods were obtained whenever possible. The surface density of LPVs is more than ten times greater than in the Sgr I Baade's window at l = 1.37o, b = -2.63o. The limits of completeness arising from interstellar and circumstellar absorption are discussed. Most of the area suffers interstellar extinction of 20 < AV < 40 mag. The shorter-period LPVs are less luminous than the longer-period ones and may be slightly under-represented in the data. Extremely heavy extinction (AV > 40 mag), which affects the probability of detecting variables, occurs in less than 25% of the area. Almost all of the LPVs are Miras or OH/IR stars, with periods ranging from 150 days to about 800 days. K-band counterparts have been found for 59% of the 109 known OH sources in the field. The average period of the variables found is 427 days, while that of the OH/IR stars is 524 days. For comparison, the average period in the Sgr I window, which contains no known OH/IR stars, is 333 days and only two stars are detected with P > 600 days. The survey field also contains a number of long-period, large-amplitude variables which are not OH emitters.

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