Posted: Wed Jun 29, 2011 4:49 pm Post subject: Two spectrophotometric standards
I would like to flux calibrate a spectrum using the data of two spectrophotometric standard stars (one red and one blue).
I was able to create two flux files, one for each star, using the task "standard". I could obtain the sensitivity function for each star separately using "sensfunc" but I did not manage to combine the data of both stars with the "sensfunc" task.
Killing IRAF task `sensfunc'
Traceback (innermost last):
File "<console>", line 1, in <module>
IrafError: Error running IRAF task sensfunc
IRAF task terminated abnormally
ERROR (741, "Cannot open file (bd330001.flx,bd260001.flx)")
The error is the same if I use IRAF or PyRAF. Hence, I suppose that it is not possible to input two files in "sensfunc" but one file with several apertures. Am I wrong? Should I combine the data in a previous task like "standard"?
SENSFUNC only takes one input in the "standards" parameter. I am not completely sure what you need. Do you have one spectrum with a large wavelength coverage and want to use standard star data where each one only covers part of the coverage? In that case what you should do is copy the standard data and merge them into a single larger standard star file. You would use this in STANDARD to produce the one file for SENSFUNC fitting.
One the other hand if you have two spectra, say from a red channel and from a blue channel, then you would things separately for each spectrum.
If I did not understand the problem you can explain in more detail the nature of the data (whether one spectrum file or not) and what the wavelength coverage is, etc.
I have one spectrum to calibrate and two spectra of two different calibration stars, all of them obtained with the same instrument and configuration. The wavelength coverage is from 350 to 700 nm and the average resolution is about 0.2 nm. My aim is to use both spectrophotometric stars for the flux calibration if possible.
At first sight, it seems like the calibration using only the blue spectrophotometric star is more reliable for the blue part of the spectrum and the calibration using the red star is more reliable for the red part of the spectrum. I was trying to combine the data of the two calibration stars in order to obtain a reliable calibration for the full wavelength coverage. After reading your answer, I think that this could be done using the task STANDARD but I cannot figure out how to do that.
The standard task is about converting a single standard observation into flux bins matching a single standard star calibration file. With multiple stars and multiple observations it accumulates all these together. I think you can accomplish what you want by running the task with the same same observation listed twice. The first time you point to one calibration and the second time to the second. (You could accomplish the same thing by running standard twice and then concatenating or letting the task append to the same output.)
In this case if there are overlapping wavelength bins in the two calibrators then they will appear in the fitting. If you only want one or the other flux bin then you can create a new calibration file by editing the two together appropriately.
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