productivity. Figure 1 shows the number of refereed publications per year based on data obtained using the WMKO from 1996 to present (please note that the 2008 numbers are incomplete). The number of refereed publications per year has increased with time. This increase in productivity can be attributed to the frontier instruments and adaptive optics systems that have been installed on the Keck telescopes over the period between first light and today.
Figure 1: Number of refereed publications per year based on data from W. M. Keck Observatory. Note that the publication numbers for 2008 are incomplete.
Keck currently produces approximately 150 papers per telescope per year, which as shown in Figure 2, exceeds the scientific output of any other ground-based observatory in the world.
The impact of papers based on Keck Observatory data also significantly exceeds that of peer observatories. Crabtree (2008, SPIE, 7016, 40) showed that Keck Observatory has the most highly and extremely cited papers and the fewest weakly cited papers compared to all other major optical/infrared telescopes (both ground and space-based). The comparator group in this study includes the ESO VLT, Gemini, Subaru and Hubble Space Telescope. A study conducted by ESO staff (Grothkopf et al., The Messenger, Volume 127, page 62, 2007) compares the scientific impact of four major observatories with 8-10 meter telescopes based on the h-index, where the counted publication number equals the number of citations, in order to not overly weight the most heavily cited papers nor lowly cited papers (Hirsch, J. E., 2005, Proceedings of the National Academy of Science, vol. 102, Issue 46, p.16569). As shown in Figure 3, they conclude that the aggregate scientific impact of Keck Observatory exceeds that of the VLT, Gemini, or Subaru. Grothkopf et al. also show that WMKO has been significantly more productive than the other three observatories even when the different start-of-science-operations dates are taken into account.