Useful files

This page documents some files that may come in useful while observing or during reduction.

CCD defects

The HiPERCAM CCDs have a number of defects, dust and the like, and, as of 13 May 2021, a hair in the upper-right quadrant of CCD 2 along with a long-standing similar feature in the lower-left quadrant of CCD 4. When acquiring targets these may not be visible so you are VERY STRONGLY ADVISED TO OVER-PLOT DEFECTS. You can also create your own using the pipeline command setdefect and you are encouraged to do so if you see a defect not already marked in whatever file you use.

Defects are classified as “moderate” (plotted in yellow) or “severe” (red). What one counts as one or the other is a matter of taste. If you are too picky, you could end up with so many defects that you are afraid to observe.

I have decided to define defects according to the following prescription: moderate: 10 to 25% deviation from the norm; severe: greater than 25% from the norm. I mark each pixel in these categories, so a really bad feature might appear in multiple pixels (there is a very nasty feature in the lower-left quadrant of HiPERCAM’s CCD 4 for example). I plan to update the files with time, and retain old ones for monitoring purposes. I identified the bad pixels using a flat field divided by a smoothed version of itself (smoothed with a 40 pixel FWHM 2D gaussian filter). I have also marked some lines caused I suspect by charge traps. These are visible in biases at least; I am unsure what effect they have when enough light is coming in.

For ULTRACAM I have also added hot pixels. Although these should at least partially be removed if you apply a dark fram during reduction, they can potentially add noise, e.g. if your target has 500 counts but sits on top of a hot pixel contributing 10000, you get noise of sqrt(10500), but still just a signal of 500 (and that’s assuming perfect dark frame correction). Clearly then the impact depends upon the target so it’s more difficult to assign severity levels. In the file for ULTRACAM below I decided somewhat arbitrarily to define a count rate of 40/sec and above as “severe”, and 15 to 40 as “moderate”. However, to help judge, hot pixels appear in the form of integers representing the count rate.

When observing, you should move the target and essential comparison stars away from any such defects, particularly those that appear in red. The zoom/pan feature of nrtplot is useful for this.

Current files:

  1. 2021-08-02 (HiPERCAM defect file) Hair on CCD 2 gone after cleaning by Vik following removal of the CCD window to fix a leak.

  2. 2021-06-09 (ULTRACAM defect file) Hot pixels marked.

  3. 2019-12-08 (ULTRASPEC defect file)

Old files:

  1. 2021-06-09 (HiPERCAM defect file) Some linear charge trap (?) features marked.

  2. 2021-05-13 (HiPERCAM defect file) New hair in upper-right of CCD 2.

  3. 2018-06-21 (ULTRACAM defect file) Added another bad column in CCD 2

  4. 2018-06-02 (ULTRACAM defect file)

  5. 2018-05-21 (HiPERCAM defect file)


Dark frames made from makedark.

  1. 2021-05-27. Made from 26x60 sec dark frames. (ULTRACAM dark frame)

Fringe maps and peak/trough pairs

Two types of files are needed to implement defringing. Fringe maps as generated by makefringe (these are standard hcm files in format), and sets of peak/trough pairs as generated by setfringe with extension “.frng” (JSON text files). Here are some pre-prepared examples to get you going, but if the z-band is important fo you, you may want to get your own calibrations:

  1. 2018-05-19, HiPERCAM fringe map. Created from runs 0018 to 0025 from the night of 2018-05-19 on the GTC, with one frame of 0019 removed because of a satellite trail. 71x120 sec dithered images in all. Smoothed with FWHM=4. (hipercam z-band fringe map)

  2. 2018-04-15, HiPERCAM fringe map. Created from runs 0035 to 0043 from the night of 2018-04-15 on the GTC, with one frame of 0038 removed because of a satellite trail. 71x120 sec dithered images in all. Smoothed with FWHM=4. (hipercam z-band fringe map)

  3. 2018-04-15, associated peak/troughs. Not necessarily definitive but a start. (hipercam z-band peak/trough pairs)