Black-Body Stars
  We report the discovery of stars that show spectra very close to the
black-body radiation. We found 17 such stars out of 798,593 stars in the Sloan
Digital Sky Survey (SDSS) spectroscopic data archives. We discuss the value of
these stars for the calibration of photometry, whatever is the physical nature
of these stars. This gives us a chance to examine the accuracy of the zero
point of SDSS photometry across various passbands: we conclude that the zero
point of SDSS photometric system is internally consistent across its five
passbands to the level below 0.01 mag. We may also examine the consistency of
the zero-points between UV photometry of Galaxy Evolution Explorer and SDSS,
and IR photometry of Wide-field Infrared Survey Explorer against SDSS. These
stars can be used as not only photometric but spetrophotometric standard stars.
We suggest that these stars showing the featureless black-body like spectrum of
the effective temperature of $10000\pm1500$K are consistent with DB white
dwarfs with the temperature too low to develop helium absorption features.
