| | 1 | A set of questions that have arisen from the analysis of the MDS 07 and 08 images at Durham. |
| | 2 | These questions are preliminary and will be updated as we learn more. |
| | 3 | |
| | 4 | 1) The width of the tracks removed by Magic are often extremely wide (10s of pixels) and result in up to 30?% of a given image be masked out. |
| | 5 | What is the prospect of getting Magic working within the specification of only a few percent masked pixels? |
| | 6 | |
| | 7 | 2) We have measured the PSF of the stacked images [g-band MD08?] to have a width of 2 arc secs whereas the data distribution table [insert link] lists the image quality as 1.2 arc secs. Why is it so bad (especially as the stack is made from only the 50% best data) and why |
| | 8 | is the quoted 1.2 arc sec wrong. |
| | 9 | |
| | 10 | |
| | 11 | 3) The stacks have very variable sky levels. This appears to come from the fact that each warp from which the stack is made has a slowly varying sky level. As masking means that different regions of the stack are partial sums of different subsets of the warped frames this leads |
| | 12 | to patchy sky in the stack with sharp discontinuties. This will prevent detection of faint extended sources. Are there plans to do a local |
| | 13 | sky subtraction in the warps or otherwise greatly improve the sky subtraction. |
| | 14 | |
| | 15 | 4) The noise in the sky background in the stacks is mottled, ie correlated over a scale comparable to the extended sources we want to |
| | 16 | detect. This is possibly an inevitable consquence of convolution to a very broad 2 arc sec PSF |
| | 17 | that is done to each warp prior to stacking, but looks far worse than those with experience of stacking expected. |
| | 18 | |
| | 19 | 5) In good seeing (~1.2 arc sec PSF) warps the images of stars are clearly not round. Some are triangular (!) others look trailed |
| | 20 | (but not coherent across whole frame and so not trailing). Is this poor focus? What are the prospects for improvement? |
| | 21 | |
| | 22 | 6) Many reasonably bright galaxies (17 mag) have cross shaped masks applied to their centres. It looks like they've been flagged |
| | 23 | as bright stars and an erroneous attempt has been made to mask out diffraction spikes. |
| | 24 | |
| | 25 | 7) The z-band images appear striped, which we think is an artificat of the correlated read noise that Ken mentioned. Is that the case |
| | 26 | and if so why is it apparent in long exposure MDS frames, especially in z where the sky brightness is high? |
