From: "Wolfgang Renz" >>> > When I looked at the FITS header I noticed that you did the > Thats probably the cause for the remaining hot pixel. > What software did you use for the bias/dark/flat processing ? > <<< > I Used MaximDL for image calibration. > I didn't think the temperature difference would matter with the > bias frames as technically speaking, no dark current should > accumulate in a zero length image. > Am I wrong in this line of thinking? If the hot pixel were cosmics, I would be surprised. With my How did you combine the bias/dark/flat/light frames ? Add, Mean; Median, MMclip, Sigma, SDM, ... ? If all the images were made at the same temperature, an explaination might be an incorrect bias/dark/flat/light processing that introduced the hot pixel. You are right. With a zero exposure, basically no dark current the dark current should double. Really zero it will just get towards 0K. But all the pixel (and especially the warm/hot pixel) have also different base ADU levels that depends on the temperature !!! I just made a quick indoor test (20 SDM combined bias frames A background area without hot pixel and cosmics gives for my - +15oC: Mean 112 ADU, StdDev 12 ADU - 0oC: Mean 104 ADU, StdDev 9 ADU but for the same hot pixel pair: Looks like as the hot pixel ADU depends pretty linearly on the temperature. So all the warm/hot pixel will appear very obviously in all subtracted image that were made at different temperatures. -> Each of the groups should be made at the same temperature ! > >>> > It might be easier and will be more accurate without bias and > scaled dark frames (using bias frames introduces additional > noise) using darks that match the light/flat frames. > Remember that the bias and dark frames will change with time. > <<< > These were new flats and darks that I've taken within the past > two weeks. I was trying to make the best of the horrendous > weather we've been having here. hot pixel (hoping you don't have unreliable pixel that already changed their behaviour. But as long you don't have a hot pixel in one of the stars you want to measure, you probably can leave it as it is. The pretty picture folks would just run a hot pixel scrubber over the final image. > >>> > Is your seeing so bad ? > Or did you defocus a bit on purpose to spill the light over more > pixel to increaed the photometric accuracy ? > <<< > The seeing that evening was very bad. The jet stream was > directly over my head and another system moved through a > few hours after I packed it in. I hope this isn't the best the FRC > can do. Actually I would be glad to get such a nice PSF profile with my camera lenses for bright star photometry. Even with slight defocusing the the central pixel stays very bright while just the halo seems to get brighter. Have you ever check the collimation of the FRC ? Clear skies Wolfgang Wolfgang Renz, Karlsruhe, Germany Rz.BAV = WRe.vsnet = RWG.AAVSO _______________________________________________