Harvard University Astronomy Lab and Clay Telescope

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Taking Calibration Spectra

Whenever you take a spectrum, you need to take a spectrum of a calibration source so you can generate a wavelength solution. Calibration spectra are best taken immediately before or immediately after your object spectrum, while being sure not to bump or disrupt the spectrograph or telescope pointing. In our lab, we have a Mercury-Argon fiber fed calibration lamp. Since this lamp does emit some UV light, it is important not to look directly at the light source.

• With the spectrograph mounted through the eyepiece, look on the bottom of the spectrograph and find the dime size metal circle. Grab a screwdriver and slightly loosen the screw and move the plate to the side so the opening is exposed.
• Plug in the calibration lamp (but do not turn the lamp on yet) and attach the fiber..
• In CCDOps, click Camera -> setup and make sure the Active CCD is set to Imaging
• Now, with everything set up, one person should hold the fiber flat against the center of the opening on the bottom of the spectrograph and turn on the calibration lamp
• Again in CCDOpps, click Camera -> Grab and enter exposure time. Make sure that Darks are turned ON.
• Check that spectrum is not overexposed! Generally, your spectrum should have between 20,000-30,000 counts and saturation is 65,000 counts.
• Take a few calibration spectrums to be sure you get a good one!
• When finished, be sure to turn the lamp off and return power cord, fiber and lamp to the appropriate box. Also, re-tighten the circle plate on the spectragraph to cover the opening.