Absolute Calibration of Stellar Temperatures

Abstract

The scale of effective temperatures T_eff is based on observed absolute radiation temperatures T_r, which are defined by Planck's radiation law where T_Au designs the absolute temperature of the gold point. A relative scale of radiation temperatures can be derived from spectrophotometric comparisons with a standard star. The absolute calibration of the standard star (α Lyr or Sun) demands a careful comparison with a standard radiation source of well known spectral energy distribution (Black Body or Synchrotron). With ground-based observations atmospheric extinction is to be taken into account; with extraterrestrial observations detectors may be used which are absolutely calibrated in a radiation laboratory under space conditions.