Helium-Argon Arc Lamp Exposure times and line identification

Helium-Argon Arc Lamp Exposure times

The values listed below are such that the brightest useful line peaks are at 40,000 - 50,000 counts. Always make sure during your run that the exposures are to your satisfaction.

Two sets of values have been listed for some of the grisms. Short exposures to keep the strongest line from saturating results in the lines at the edge(s) of the CCD, the only ones there, being faint.

These values are valid for:

  • 2x2 Binning : Multiply them by 4 for 1x1 binning, and
  • 1" slit : For a 0.5" slit the times should be doubled, whereas for a 2" slit the exposures should be halved.
  • Grism  Helium 
    exposure
    (seconds)
    Argon 
    exposure
    (seconds)
    Notes 
    Gr#01  2.0 0.4 He 5876 and Ar8115 saturated; faint lines at the red and blue extremes better
      1.0 0.25 No line is saturated; the peripheral lines are faint
    Gr#02  1.0 0.07 Two Ar lines saturate even with the lowest possible exposure
    Gr#03  2.0 10.0  
    Gr#04  1.25 1.75 No line is saturated
      2.5 1.75 He 5876 is saturated but the blue lines are brighter
    Gr#05  0.8 0.2
    Gr#06  2.0 0.3 He 5876 saturated; lines at the blue end are better
    Gr#07  15.0 30.0 The strongest Ar peaks are < 20,000 counts
    Gr#08  2.0 30.0  
    Gr#09  5 60.0 He 5876 saturated; faint blue lines stronger against the Ar "continuum". Grism 9 replaced by grism 18
    Gr#10  2.0 0.4 Grism 10 decommissioned
    Gr#11  3.0 3.0 He 5876 saturated; lines at the blue end are better
    Gr#12  3.0 0.3 Grism 12 replaced by grism 16
    Gr#13  2.5 0.6 He 5876, Ar 7504 and Ar 8115 saturated; faint blue lines stronger 
    Gr#14  30.0 30.0  
    Gr#15  3.0 0.3 Grism 15 replaced by grism 17
    Gr#16  3.0 0.3  
    Gr#17  3.0 0.3  
    Gr#18  2.5 60  
    Gr#19  15 30  
    Gr#20  0.1 30  

    Helium-Argon Line Identification

    Only the principal lines have been marked on the plots. The wavelengths of other lines may be found in HeAr Line list. This list includes lines from the IRAF database plus a few lines not listed there. Typically one may expect to utilise 15-25 lines for the wavelength calibration and have a scatter of 1/50 - 1/10 of the resolution element.

    The Helium lines have been labeled in blue and the Argon lines in red. While lines of the same element are expected to have constant relative intensities the relative intensities of the helium and Argon lines will naturally vary with the  exposure times  used.

    Grisms  PS files
    Gr #1 28 Kb 
    Gr #2 172 Kb
    Gr #3 29 Kb 
    Gr #4 25 Kb 
    Gr #5 26 Kb 
    Gr #6 29 Kb 
    Gr #7 25 Kb 
    Gr #8 24 Kb 
    Gr #9 24 Kb 
    Gr #10 28 Kb 
    Gr #11 25 Kb 
    Gr #12 27 Kb 
    Gr #13 24 Kb 
    Gr #14 28 Kb 
    Gr #15 25 Kb 
    Gr #16 27 Kb  (Gr #12)
    Gr #17 25 Kb  (Gr #15)
    Gr #18 24 Kb  (Gr #9)
    Gr #19  
    Gr #20