Data Caveats


  • (Added Sept. 16, 1999) Background smoothing: The header of the first binary table extension of each ORFEUS-I file contains the line 

    TTYPE9  = 'BACKGROUND'    / normalized background, smoothed by 6 pixels

    In fact, the BACKGROUND spectrum for every BEFS observation is smoothed by 13 pixels (2 x 6 + 1) along the X dimension, as reported in the primary file header: 

    HISTORY   Background Average: 13 pixels in X

    This error will be corrected in the ORFEUS-II data set.

  • (Added Sept. 16, 1999) EUV/FUV Exposure times: For at least one set of observations, the EUV observation does not have the same integration time as the FUV.

  • (Added Oct. 10, 1999) Effective area: Since submitting the ORFEUS-I data set to the archive, the BEFS project has determined that the second-order effective-area curve for Spectrum D is somewhat high at long wavelengths. (It overpredicts the flux of the second-order He I 584 Å line by 25%.) The curve was generated theoretically and normalized to the observed FUV flux at wavelengths below 912 Å, so should be correct at short wavelengths. The BEFS project recommends that users rescale the effective-area curve (or equivalently, the second-order counts spectrum) using a linear function equal to 1.0 at 912 Å and 0.8 at 1168 Å.

  • Errors in the FITS header keywords were discovered by Dr. Van Dixon in the files listed below. In each case, the listed coordinates were also found to be incorrect. Note: corrected files were archived on March 13, 2000, so only files requested before this date are affected.

    BEFS1017 & BEFS1019 - The target is listed as NGC 346, an open cluster. In fact, NGC 346 WB 1 was observed, a particular star in the cluster.
    BEFS1023 - SIG CRB is actually SIG2 CRB (there's a difference), or more usefully, HD 146361.
    BEFS1080 - This is not NOVA SGR 1994, but NOVA SGR 1993.
    BEFS1085 - This airglow spectrum is not a failed pointing at PG 1159, but a failed pointing at RX J2117.1+3412. See below.
    BEFS1106 - The star labeled PG 1159 is not PG 1159 itself, but a PG 1159-type star called RX J2117.1+3412.
  • 2001-04-04 Spectra obtained through channels A and B (wavelengths shorter than about 700 Å) exhibit a number of effects that complicate their interpretation. On ORFEUS I, the "bright corner" contaminates Grating A spectra at wavelengths shorter than about 420 Å. On ORFEUS II, the Grating A spectrum crosses, not the bright corner, but the Grating B spectrum, contaminating both in the regions 420-460 and 550-590 Å, respectively. In addition, there is some uncertainty in the absolute photometry of our EUV data, especially on the ORFEUS II mission. As a result, researchers are advised to use caution when analyzing EUV data from the ORFEUS mission and to check the scaling of second-order spectra (when provided) before subtracting them from FUV spectra.

  • The keyword "filter" has a non-null value only for ORFEUS-2 spectra of EPS CMA, which were obtained through a tin filter, labeled SPB3.

    This information was provided by Dr. Van Dixon of the Space Sciences Laboratory, The University of California, Berkeley.