2005/07/07 by William T. Reach, William T. Reach, S. T. Megeath +14
Physics and Astronomy · #Adaptive optics and wavefront sensing #Astronomy and Astrophysical Research #Brightness #Cepheid variable #Ecliptic #Infrared #Photometry (optics) #Spitzer Space Telescope #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/432670
published as Publ.Astron.Soc.Pac.117:978-990,2005 · accepted to PASP; 7/7/05: fixed mistake on page 17 (extended source corrections must be multiplied not divided)
arxiv created 2005/07/07 · openalex publication_date 2005/09/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The Infrared Array Camera (IRAC) on the Spitzer Space Telescope is absolutely calibrated by comparing photometry on a set of A stars near the north ecliptic pole to predictions based on ground-based observations and a stellar atmosphere model. The brightness of point sources is calibrated to an accuracy of 3%, relative to models for A star stellar atmospheres, for observations performed and analyzed in the same manner as the calibration stars. This includes corrections for location of the star in the array and the location if the centroid within the peak pixel. Long-term stability of the IRAC photometry was measured by monitoring the brightness of A dwarfs and K giants (near the north ecliptic pole) observed several times per month; the photometry is stable to 1.5% (rms) over a year. Intermediate-time-scale stability of the IRAC photometry was measured by monitoring at least one secondary calibrator (near the ecliptic plane) every 12 hr while IRAC is in nominal operations; the intermediate-term photometry is stable with a 1% dispersion (rms). One of the secondary calibrators was found to have significantly time-variable (5%) mid-infrared emission, with period (7.4 days) matching the optical light curve; it is possibly a Cepheid variable.