ISIS cosmic rays filter problem with Alpy
Posted: Sat Apr 14, 2018 9:12 pm
Hello,
It seems I've hit either a severe bug or a misuse of "Cosmic rays filter" in ISIS with the Alpy (f/4 Newton, ATIK 414, bin1x1, 18 and maybe 23 micron slit).
In the past, always enabled this feature above 5 minute by default.
When the signal is high, enabling the checkbox "Cosmic rays filter" alters the result this way, like cutting the sharp peaks (red is the filtered): Not to mention, this filter is be rather harmful when signal is high.
FHWM Y: = 2.22 - 2.45
ISIS version: 5.7.0 (I know behind the latest, but later features in the whatsnew list are all out of my use case).
I did notice this feature is harmful for the reference stars already, but never thought real spectra - mostly emissions - are affected so badly.
The manual here is hard for me to interpret:
http://www.astrosurf.com/buil/isis/quic ... ced_us.htm
"... Do not filter the cosmic rays in case of need (when observing faint objects)."
Does it read as we should leave it switched off for all the non-faint objects? (for the UV, yet long exposures needed, cosmic rays possible)
Note that altering the cosmic filter "value" between 10-100-10000 doesn't change anything.
For now, just alerting the Database that many of my high-SNR Alpy results might be hit by this error, and requires a large review + reprocessing effort from my side in the future.
Peter
PS.: a fits header update containing the altered range would be welcome.
It seems I've hit either a severe bug or a misuse of "Cosmic rays filter" in ISIS with the Alpy (f/4 Newton, ATIK 414, bin1x1, 18 and maybe 23 micron slit).
In the past, always enabled this feature above 5 minute by default.
When the signal is high, enabling the checkbox "Cosmic rays filter" alters the result this way, like cutting the sharp peaks (red is the filtered): Not to mention, this filter is be rather harmful when signal is high.
FHWM Y: = 2.22 - 2.45
ISIS version: 5.7.0 (I know behind the latest, but later features in the whatsnew list are all out of my use case).
I did notice this feature is harmful for the reference stars already, but never thought real spectra - mostly emissions - are affected so badly.
The manual here is hard for me to interpret:
http://www.astrosurf.com/buil/isis/quic ... ced_us.htm
"... Do not filter the cosmic rays in case of need (when observing faint objects)."
Does it read as we should leave it switched off for all the non-faint objects? (for the UV, yet long exposures needed, cosmic rays possible)
Note that altering the cosmic filter "value" between 10-100-10000 doesn't change anything.
For now, just alerting the Database that many of my high-SNR Alpy results might be hit by this error, and requires a large review + reprocessing effort from my side in the future.
Peter
PS.: a fits header update containing the altered range would be welcome.