Spectral

Technical Data for Spectral Camera

Images acquired with the Spectral camera on Faulkes Telescope North (FTN, at Haleakala Observatory) occasionally show a pseudo-nebulosity with the pattern of the detector's surface features. The pattern suggests that the images were either flat-fielded improperly or not at all. The images may have been compromised by one of several flat-field-related factors:

• The gain of the Spectral camera is nonuniform over the dynamical range ("non-linearity"). Raw flats are acquired with varying levels of counts: the twilight sky illumination varies, depending on whether the skies are partly cloudy or the order in the sequence of filters. If, for example, a master flat is created from very bright raw flats and then used to flat-field a science image (with a low background), the extreme levels of the master can be transferred to the reduced science image.
• The bias level of the Spectral camera fluctuates intermittently. If the bias level changes during the night, then the bias frames collected before the start-of-night are inappropriate for bias subtraction. We do not yet have a procedure for detecting such a change and modifying the data pipeline in real-time. So far, the fluctuations have occurred just frequently enough to be annoying and occasionally lead to a set of images being unusable.
• On nights around full moon, images acquired with the 2m telescope pointed generally north show a larger-than-expected background brightness. We believe that this increase in brightness occurs because of moonlight reflected from other buildings at Haleakala Observatory, which are all north of FTN.

Description of Standard filters