Mid-Infrared Calibration of a Dense Spatial Network ofStars for Accurate Absolute Spectrophotometry: a NewApproach for a New Generation of Telescopes

摘要

The next frontier for calibration is the new generation of 8 and 10-m telescopes. Visible and near-infrared calibration for these telescopes have rel-atively simple solutions, but the mid-infrared is more complicated and arguablythe most important range to calibrate given the paucity of good calibrators andthe difficulties that the mid-infrared sky provides, even for a low water vapoursite such as the Roque de los Muchachos Observatory in La Palma where thecolumn of water vapour is below 2-mm for a substantial fraction of the year. We report on our calibration programme, which is in the final stages ofpreparing a dense network of accurate northern-hemisphere standards for the3.5-25 micron range for CanariCam, the mid-infrared instrument of the SpanishGran Telescopio Canarias (GTC). Our goal is to provide approximately one starper ten degrees square north of declination —40°, with a goal of 2% error inthe absolute photometry at the short wavelength end and 10% at 25 microns.We describe the selection, observation and modelling of these stars and thecharacteristics of our final sample of calibration sources. Nearly 1000 candidate stars were choosen from an initial sample of some25,000 input stars selected from a variety of sources. Of these we have observa-tions of more than 650 stars from which our final sample of calibrators will betaken. We describe the selection, observation and modelling of these stars andthe characteristics of our final sample of calibration sources.