Spectroscopy on Small Telescopes: the Echelle Spectrograph

In recent years there has been a trend toward the automation of modest sized observatories, especially those involved with photoelectric photometry. Although undoubtedly useful, there is clearly a need for more advanced instrumentation such as spectrographs. The relatively small telescope sizes places severe limits on the choice of spectrograph configuration. A fiber-fed echelle spectrograph is arguably the most suitable design for these applications. Presented here is a brief discussion of the design philosophy and operating principles. Both theoretical and measured performance data for the prototype University of Queensland Echelle Spectrograph are also presented. Modest sized telescopes, that is telescopes of less than 1 metre aperture, are playing a far more important role in astronomy today than ever before. Apart from the obvious applications of visual observing and astrophotography, this class of instrument has become a vital tool for photometric observations, especially when extended observation runs are required. One such example is the study of variable stars using stellar photometry. Occasionally, however, the object being observed may exhibit an ‘outburst’ or sudden significant increase in light output. If this occurs then supporting spectroscopy can yield important additional information about the nature of the outburst. Unfortunately, in most cases, access to a suitable telescope and spectrograph at only a moments notice is rarely possible. This is just one example of how the inclusion of more advanced instrumentation, such as spectrographs would be a great advantage. 1. Design Philosophy When considering a spectrograph for use on telescopes of less than 1 metre aperture, there are major implications for the design of the spectrograph. For the spectrograph to be mounted on the telescope it would have to be both small and of low mass. Even the larger telescopes often used in robotic observatories have little space for additional instrument packages. Fortunately this can be solved by mounting the spectrograph away from the telescope and using an optical fiber to transfer the light. Although no longer mandatory, a compact design is still desirable to allow installation in smaller observatories. Transportability, and the possibility of Astrophysics and Space Science 273: 217–224, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands.