Auxiliary fuv mama dark files provided for users
(1) Mean dark rate including glow normalized to counts/pixel/second
(2) hot pixels (>1e-4 c/s) + base level measured in dark corner
(3) glow only (1) minus (2)
Data provided for 5 epochs
| Epoch | Date range | Avg in glow region [400:800,1200:1600] |
Avg in dark corner [1800:2000,20:220] |
number hot pixels >1e-4 |
total exp time(s) |
|---|---|---|---|---|---|
| epoch1 | Apr 1997 - Aug 1998 | 3.597E-6 | 1.644E-6 | 87 | 178803.5 |
| epoch2 | Aug 1998 - Nov 1999 | 1.079E-5 | 1.652E-6 | 428 | 173880 |
| epoch3 | Dec 2000 - May 2001 | 1.236E-5 | 1.605E-6 | 1431 | 194580 |
| epoch4 | Mar 2002 - May 2003 | 1.539E-5 | 1.563E-6 | 2607 | 161280. |
| epoch5 | May 2003 - Aug 2004 | 1.647E-5 | 1.541E-6 | 2489 | 172500. |
Average of dark monitor exposures for each epoch, normalized to counts/s
(right click on the name of the file to dowload it to disk or download directly from
ftp://ftp.stsci.edu/cdbs/stis_aux/
fuv_dark_epoch1_mean.fits
fuv_dark_epoch2_mean.fits
fuv_dark_epoch3_mean.fits
fuv_dark_epoch4_mean.fits
fuv_dark_epoch5_mean.fits
Hot pixels (>1e-4 c/s) plus average rate measured in dark corner
fuv_dark_epoch1_base_plus_hot.fits
fuv_dark_epoch2_base_plus_hot.fits
fuv_dark_epoch3_base_plus_hot.fits
fuv_dark_epoch4_base_plus_hot.fits
fuv_dark_epoch5_base_plus_hot.fits
Glow only. Mean dark minus hot pixels minus dark corner average
fuv_dark_epoch1_glow_only.fits
fuv_dark_epoch2_glow_only.fits
fuv_dark_epoch3_glow_only.fits
fuv_dark_epoch4_glow_only.fits
fuv_dark_epoch5_glow_only.fits
Recommended procedure for subtracting the fuv dark glow from a science image.
- Flag hot pixels (>1e-4 c/s in mean dark) and remove them from the raw science image (set to average "dark corner" dark rate or to median of surrounding pixels).
- Subtract average "dark corner" dark rate from the hot pixel cleaned raw science image to produce an intermediate raw science image.
- Smooth the appropriate "glow only image" with a guassian smoothing kernel to reduce pixel-to-pixel noise in the dark. The size of the best smoothing kernel will depend on the nature of the science data and the science goals.
- Find a region in the science image where the dark glow is strong and the real external signal from the source is negligible (for long split spectroscopic observations, the part of the detector obstructed by the aperture bars might be suitable. Look at the wavecal image to find where this is). Use the dark rate in this region to scale the smoothed glow only image.
- Subtract the scaled glow image from the intermediate raw science image produced in step 2.
- Run the resulting image through calstis (with "DARKCORR" now set to omit) to perform other calibration steps such as flat field correction, and spectral extraction. Faint point sources are likely to require a customized spectral extraction (see STIS data handbook).