T-ReCS Spectroscopic Calibration Stars

Starting in Semester 2005B Phase II Science Programs must specify two telluric calibration stars, one that would match the airmass of the target if observed before it and one that would match it if observed after. The Gemini Staff member at the telescope will select one of these for baseline calibration, which will not be charged to the science program. If the PI desires both calibration stars or any additional calibration stars to be observed, these additional calibrations will be charged to the science program. The PI should factor into their choice of calibration stars the amount of time to be spent observing the science target. If, for example, the science target requires two hours, ideally the first standard would have an RA 1 hr less and a Dec equal to the science target.

At low resolution B, A, F, and G stars have smooth spectra in the 7-25um region, and therefore may be used to correct for atmospheric absorption features. In late K and M stars the fundamental vibration-rotation band of SiO significantly depresses the spectrum at 7.5-10um and therefore affects ratios (see eg Cohen & Davies 1995, MNRAS, 276, 715, Fig. 3). Thus late K and M stars should be avoided. A list of B, A, F, and G stars that are likely bright enough for observations in the mid-infrared is available. They are excellent for the removal of telluric features, but their mid-infrared fluxes are in general not well known and thus are not useful for flux calibration of spectra.

Early K stars (K0III-K2III) may be used at low resolution for spectra from 8-13um with minimal SiO contamination. Many "Cohen standards" are early K dwarfs and have the added advantage of having accurate mid-infrared flux densities, making them decent spectrophotometric calibrators (i.e. they provide telluric subtraction and flux calibration).

Several of the stars in the list of very bright mid-infrared standards in the Southern Hemisphere that are commonly used by the T-ReCS Team are also useful spectrophotometric calibrators.

Last update June 7, 2005; J.M. De Buizer (adapted from T. Geballe)