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Checking CCD Photometry Before Upload for Beginner

msheald's picture
Joined: 2010-10-02

Hello! I just finished my first analysis of a set up images of T PYX, and I was wondering if someone might check it to be sure that I've done things correctly and filled out the forms correctly before uploading the observations.

    I have an Meade 8" LX200 Classic and SBIG ST-402 with BVIC filters. I used MPO Connections to get a number of observations of variables in Pyxis on 1-April. Through an error in the script, I only obtained I filtered images. I just finished an analysis of T PYX.

    I used AIP for Windows version 1 to stack three images. I calibrated the image using the the advanced protocol to scale a stack of 25 minute darks and Bias frames at -5 degrees and flats from a light box. As I get into MPO Canopus more, I may switch to thta program to calibrate images.

    I used MPO Canopus for the data evaluation. Since I only had I filtered images, only two comparison stars in the CCD list had Ic values - label 113 and 115. I used one as the comp and one as the check.

    Canopus yielded a magnitude of 15.447 with an error of 0.041.

    One thing I'm interested in is the annular sizes. There is a faint star of similar magnitude close by. I tried to put it into the zone between the star and the sky background, but I'm not sure the best way to size the sizes.

    Once I'm a bit more confident that I'm following the appropriate steps, I'll evaluate my other images. Thank you for your consideration. Best regards.

Michael A. heald

T Pyx Photometry
HBB's picture
Joined: 2010-07-24

Hi Michael,

if you send me the calibrated image I would be happy to perform photometry on it and let you know how it compares to your result.  Let me know what aperture sizes you used.  You can email the image to me at if it's not too large or send it to me via Dropbox or some other method.  I can perform photometry via several different programs and let you know how they compare.


Barbara Harris (HBB)

T Pyx images
HQA's picture
Joined: 2010-05-10

Hi Michael,

One thing I would be cautious about is the dynamic range in your image.  You indicate that T Pyx was measured at Ic=15.447, and that you were using two comps that are approximately Ic=10.7.  This means that the comps are about 4.7 magnitudes brighter than the variable, and I would be suspicious that they might be saturated.  Look at the peak ADU for each of the stars, and make sure that they are under the saturation level of your sensor.

If they are saturated, then you need to use fainter comparison stars, or get another night of data where you do have B & V images and report your measures of those.  Or, a third option is to submit a CHET request:

and ask for the sequence team to fill in some more Rc/Ic values.


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