GSAOI-GEMS (Gemseeing)

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This topic contains 8 replies, has 3 voices, and was last updated by  Saracino Sara 5 years, 1 month ago.

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    Daniela Opitz


    I am trying to use the GEMSEEING task to get a estimation of the FWHM for each GSAO image I have.

    This task works well but I have a WARNING: – GEMSEEING: Instrument GSAOI not in database. Using parameter file values so I think the values delivered are not completely right.

    I inspected the file gemseeing.dat and confirmed that GSAOI is not there.

    # Copyright(c) 2000-2006 Gemini Observatory, AURA
    # Database for
    # Version Nov 5, 2001 IJ
    # Instrument pixelscale datamax fwhmin radius buffer width
    # “/pix ADU/pix arcs pix pix pix
    DEFAULT 1. 40000 3.00 0 8 2
    NIRI-f6 0.116 40000 0.5 0 20 4
    NIRI-f14 0.050 40000 0.5 0 40 4
    NIRI-f32 0.022 40000 0.25 0 100 4
    Hokupaa+QUIRC 0.01998 30000 0.08 0 100 4
    Hokupaa/QUIRC/Ded 0.01974 30000 0.08 0 100 4
    QUIRC 0.033 30000 0.5 0 8 2
    oscir 0.089 40000 0.5 0 20 4
    OSCIR 0.089 40000 0.5 0 20 4
    GMOS-N 0.0727 100000 0.6 0 20 4
    GMOS-S 0.0730 100000 0.6 0 20 4
    AO-SIM 0.0196 1E9 0.08 0 100 4
    PFC 1.355 40000 4.065 0 8 2
    pfc 1.355 40000 4.065 0 8 2
    FLAMINGOS 0.078 40000 0.5 0 30 3
    hrwfs 0.120 60000 0.5 0 20 4
    TReCS 0.0896 65535 0.5 0 20 4

    I guess that I just need to add a line to the gemseeing.dat with the GSAOI information but I am not sure about all the parameters. I know the pixel scale (0.02”) and the datamax (50000) but I don’t know about the rest.

    If I am right, which values should I write for fwhmin, radius, buffer and width parameters?


    • This topic was modified 4 years, 8 months ago by Joanna Thomas-Osip Joanna Thomas-Osip. Reason: moving this topic to the data reduction forum

    Hi Daniela,

    I have posted versions of the files you need (gemseeing.dat and gemseeing_strehl.dat). There are some big caveats, however. So buyer beware and use at your own risk…

    I was attempting to use gemseeing to get an estimate of the AO corrected fwhm for QA purposes and gave up with this route. The basic problem I ran into and couldn’t figure a way out of was that, especially in sparse fields, is that gemseeing appears to overestimate average fwhm. Due to the fact that the correction varies across the FOV, the amount of overestimation is dependent on how many sources are outside the region of good correction which is of course dependent on the guide star constellation. Furthermore, the gemseeing_strehl.dat file is full of just my best guesses. Since we decided not to go that route, I never asked the AO scientists for a calculation. If all you want is FWHM, this may not be important.

    Joanna Thomas-Osip


    Daniela Opitz

    Thanks a lot


    Saracino Sara

    I need to calculate the Strehl ratio for some images obtained with GeMS-GSAOI. I would use the task ‘gemseeing’ of the GEMINI package for IRAF but when I insert GSAOI as Instrument, I get the following warning:

    WARNING: – GEMSEEING: Instrument GSAOI not in database

    and I do not get any output value of the Strehl ratio.
    For this reason, I need to find the database named ‘gemseeing.dat’ and ‘gemseeing_strehl.dat’, to add, if missing, the information for GSAOI.
    I tried, without success, to search both files in different tasks of the GEMINI package.
    Can you tell me how to find these files?

    Many thanks in advance,
    Sara S.


    Hi Sara,

    You can try the files attached to my previous post but please read the post for important caveats.



    Saracino Sara

    Hi Jo,
    I already opened the file attached to your previous post, but I would need to find the same two files within IRAF to modify them.
    In other words, I would like to understand where are these two files that the task gemseeing called with the name DATABASE and STDATABASE.
    I hope to be more clear this time.

    Thank you very much,
    Sara S.


    Hi Sara,

    The default files are located in the gemtools directory of the gemini_iraf package. In my Ureka1.5.1 installation the path is the following:

    Alternatively, so as not to overwrite the originals, just put them in your working directory and specify path and filename in the gemseeing parameters DATABASE and STDATABASE.

    Hope that helps,


    Saracino Sara

    Thank you very much,
    your instructions have been really helpful!



    Saracino Sara

    I have another problem with the same task ‘gemseeing’.
    In fact, after adding to the previous two files the information on GSAOI, I’m trying to compute the Strehl Ratio for a GSAOI image.
    For this reason I impose as optional input (coords) a list (x,y) of coordinates and also fl_useall = yes and maxnobj = 200 because I need to obtain SR for all the stars in my list.
    However I get the following error in output:

    WARNING – GEMSEEING: Existing coordinate file is not from daofind
    caution: column x_psf will be truncated
    caution: column y_psf will be truncated
    ERROR: Attempt to access undefined local variable `y_psf’.

    “listpix (t_image//”[“//int(x_psf+0.5)//”,”//int(y_psf+0.5)//”]”) | \”
    line 1246: gemtools$
    called as: `gemseeing (mode=h)’

    I get the same error also imposing coords = default.

    Does anyone know this error and can help me to solve it?
    Thank you very much!

    Sara S.

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