Tying Spitzer's IRS Calibration to IRAC: Observations of IRS Standard Stars

We present 3.6 and 4.5 mu m photometry for a set of 61 standard stars observed by Spitzer's Infrared Spectrograph (IRS). The photometry was obtained with the Infrared Array Camera (IRAC) on Spitzer in order to help tie the calibration of IRAC and the IRS, which had been anchored to the calibration of the Multiband Infrared Photometer for Spitzer. The wavelength range of the IRS data only slightly overlaps with the IRAC 4.5 mu m band and not at all with the 3.6 mu m band. Therefore, we generated synthetic spectra from spectral templates of stars with the same spectral types and luminosity classes as our sample stars, normalized to the IRS data at 6-7 mu m, and compared those to the observed photometry. The new IRAC observations of IRS standard stars demonstrate that the two instruments are calibrated to within 1% of each other.