IRS: Calibration: Extended Sources

I. Extended Source Calibration: Main Page

Introduction:
Extended sources need to be calibrated differently than point sources because the flux fills the slit. In principle, an extended source with a known surface brightness distribution and spectrum should be sufficient to derive the calibration. However such a source does not exist -- sources like the Moon are too bright for the IRS. The zodiacal background is another extended source which can be used but it is weak and its spectrum and strength are not well known. Moreover, they vary from region to region. Thus an absolute calibration for extended sources is not possible. The best we can do is to derive an approximate calibration to give users an idea of the extent of the correction that may be required. -- our approach is described in these pages.