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We report third epoch observations of the central parsec of the Galaxy at 2.2um using the PROTOCAM imager on the NASA IRTF. We now have comparable data sets from the summers of 1991, 1992, and 1993, all obtained with the same instrumental configuration [0.3 arcsec pixels]. The data from each year were reduced in an identical fashion, with the bright, compact source IRS1-W used as the photometric reference. The conclusions presented here are based on comparison of data obtained under similar seeing conditions [as estimated from the image of IRS-7] at the different epochs. We had previously reported [Tamura et al, BAAS, 24, 1301, 1993] that a new component of IRS10 was seen in 1992 about half a magnitude brighter than in 1991. The 1993 data add the following results:
1. The sources IRS9 and IRS 12N were about 0.4 mag brighter (uncertainty 0.05 mag) in 1993 than in 1991. This continues a trend apparent in the 1992 data, which suggested that each of these sources brightened by about 0.15 mag between 1991 and 1992.
2. The source IRS28 was 0.2 mag brighter in 1993 than in 1991; its 1993 brightness is comparable to that observed in 1992. IRS14SW appeared about 0.2 mag fainter in 1993 than in the previous two years.
3. The new component of IRS10 seen in 1992 was absent in 1993.
None of the other sources within the region studied, some two dozen in total, showed convincing evidence for year-to-year variability at the 0.1 magnitude level. --------------------------------- *Visiting Astronomer, Infrared Telescope Facility, University of Hawaii
Work carried out in part by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration
