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Calibration

In addition to science observations, it is generally necessary to observe a comparison object for each TEXES spectral setting to allow removal of atmospheric absorption features and to correct residual flat-fielding errors. In some cases the comparison object can also provide flux calibration information, although flux calibration is necessarily uncertain due to TEXES' narrow slit.

Due to molecular features in their spectra, K and M stars do not make good comparison objects. Asteroids are generally the best choice longward of about 10 um, and asteroids brighter than 100 Jy (N = -1) are usually available, although not typically near a target. Hot stars (spectral type A, typically) are often preferred at shorter wavelengths. See the MIR Resources pages for more information on standard stars.

Unlike the case with other Gemini instruments, PIs must include time for telluric standards in their proposals. For programs involving bright objects where the on-source integrations are short the additional time needed for these telluric standards can lead to a factor of 2 increase in the total time requested, in the case where every science observation is preceeded by or followed by a telluric standard observation. A rule of thumb is to allow 30 mintues clock time for a telluric standard observation, which includes time slewing to the standard, setting up, and taking the observation. The actual time needed may turn out to be shorter than this on the average, but we do not yet have enough experience with the use of TEXES on Gemini to give a more accurate estimate. The actual time needed will depend on what asteroid is chosen and the wavelength of the observation.

Prospective PIs are encouraged to check the type of standards that are needed and how long they are likely to take with members of the TEXES team, since both of these things are very wavelength dependent.

Note that there are no separate wavelength calibration observations required for TEXES, as wavelength calibration for science spectra is derived from near-simultaneous spectra of the atmospheric emission, which contains numerous lines.