Dome design of JNLT

Abstract

In recent years, it has become increasingly clear that the dome is often itself a major source of seeing degradation, due to its adverse thermal properties. In order to enable the Japanese National Large Telescope (JNLT) to attain the highest image quality as a ground-based telescope, 0.1″ r.m.s. on 80% light energy diameter basis is budgeted to the dome-induced seeing degradation as a design goal. Feasibility of this goal has been studied, using the latest design concept of the dome, in the following manner.

• - Model the JNLT dome on the latest design plan for dynamic thermal analysis.

• - Perform the dynamic thermal analysis to attain temperature distribution in the dome.

• - Predict the seeing degradation induced by the dome using the thermal analysis result.

Although this study is just on an elementary level, the result indicates that our design goal is attainable on an extension of the current design concept and the dome cooling by thermal emission is a key factor we have to overcome to minimize the dome-induced seeing degradation.