Spectral characterization of HST calibration lamps: new Pt/Cr-Ne line catalogues and aging test

Abstract

The Space Telescope European Coordinating Facility's (ST-ECF) lamp project, funded directly by the European Space Agency (ESA), is dedicated to the study of hollow cathode calibration lamps as they are used onboard the Hubble Space Telescope (HST). There are two main objectives: First, we have measured the spectra of Pt/Cr-Ne lamps in order to obtain accurate and reliable wavelengths for all emission lines between 115 and 320 nm. This wavelength range corresponds to the coverage provided by the Space Telescope Imaging Spectrograph (STIS) Echelle modes. Extensive laboratory measurements were performed at the National Institute of Standard and Technology (NIST) using their 10.7 m normal incidence spectrograph and a Fourier Transform Spectrograph. Until now no good laboratory wavelengths for Cr had been available and their addition has a major impact on the wavelength calibration, in particular in the near UV. The new line list is being used in conjunction with the physical instrument model of STIS which is employed to derive an improved wavelength calibration as part of the STIS Calibration Enhancement (STIS-CE) effort. Second, we attempt to gain a better understanding of the performance of such lamps and the physical processes involved in their long term operations. Among the issues studied are the change of the spectrum as a function of current, its change as a function of time and the tolerances of alignment. The bulk of the measurements were performed on flight spares from STIS and on new space qualified lamps for the accelerated aging test. The original flight lamps from the Faint Object Spectrograph (FOS) and the Goddard High Resolution Spectrograph (GHRS) are the only lamps ever to be measured after their return from space. Together with the spectra archived from six years of on-orbit operations they provide a unique data set for studying ageing effects in these lamps. The new Pt/Cr-Ne line list has been successfully applied in the STIS-CE effort. Thereby the ST-ECF's lamp project directly leads to an improvement in the quality of scientific observations of existing HST spectrographs. Our findings also constitute important lessons for the design and operations of future UV and optical spectrographs in space.

The spectrum of Th-Ar hollow cathode lamps in the 900-4500 nm region: establishing wavelength standards for the calibration of VLT spectrographs

“…At higher lamp current more ions are available in the plasma and there is a corresponding increase in sputtering. A similar analysis for Pt/Cr-Ne lamps has been done by Kerber et al 24,25 Based on these findings one can devise ways to optimise the use of the lamps for CRIRES calibration. For example, the lamp could be run at higher currents for longer wavelength regions where the intensity and spectral density of lines is intrinsically lower.…”

Design for a portable calibration system for the Full-sun UV Rocket SpecTrometer instrument

“…The lamp is a platinum HC source with a custom magnesium fluoride window to pass the spectrum of interest similar to that used for HST calibration and studied. 4,5,6 The spectral emission from such sources is known to 0.001 Å thereby providing the key spectral calibration standard. In addition to vacuum pumps and pressure measurement sensors, a residual gas analyzer will be installed onto the chamber to monitor contaminant gases, such as water vapor, which absorb strongly at Lα.…”