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question about magnitudes

EIU's picture
EIU
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Joined: 2011-12-20

What might be some of the causes of this problem? The time series for the variable star is relationally consistent with other observations, but the whole series is moved up the magnitude ladder to the brighter side by about 10 magnitudes ( a 9.0 variable star is registering as -3 )?

 

eiu

 

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strange twist to problem
EIU's picture
EIU
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Joined: 2011-12-20

after playing around a lot more, I have discovered that vphoto lists the right magnitude for the variable star when I analyze single image by single image, but lists the star as 10 magnitudes less when i try to combine images in a time series. I could analyze each photo individually, but there are 162 of them and I feel like there should be a solution to this problem. Anyone have any ideas. Is this vphoto being weird, or am I doing something wrong?

 

eiu

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Filter / sequence problem?
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kge
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Joined: 2010-07-19

Are your images taken with a filter other than the standard ones that VPHOT recognize? Or if it is a standard one, does the FILTER key in the FITS header contain a 'standard' letter for identification? VPHOT will recognize B, V, R etc.

You might get time series results like that if VPHOT does not know what sequence to apply. In that case pure differential magnitudes are used.

There are several ways to fix the problem:

1) If the filter is a standard one, make sure a standard letter is written in the FITS header as images are taken (best solution). That will make everything work out of the box.

2) If that is not possible, make sure to select a standard filter as you upload the images.

3) To avoid uploading the images you already have uploaded, mark the images in the image list, click the Rename link, and select which filter these images was taken with. Then create a new sequence and re-run the analysis.

4) If the images was taken with a non-photometric filter, you will probably not be able to submit the results to AAVSO anyhow, nor find a sequence for the comp stars. But you CAN still get results by entering a magnitude for one of the standard sequences for the comp star(s) by clicking Edit Sequence in the info pop-up box when clicking a star. Then, on the time series results, select V in the Sequence drop-down and click Refresh.

Geir 

thanks for the advice! The
EIU's picture
EIU
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Joined: 2011-12-20

thanks for the advice! The fits header contains "green" for its filter information. It seems to recognize this when I upload the photos, as everything is listed as a green filtered image in the image list. However, when I analyze a single image, it lists the filter as green but also asks me what filter setting I want to use when analyzing the images. So I think you might be right. I will have to see what I can do with the fits headers of the images and report back if the problem still persists. Thanks again!

 

eiu

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Unfortunately, even though I
EIU's picture
EIU
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Joined: 2011-12-20

Unfortunately, even though I was able to rename the photos and get vphoto to recognize the v filter, the problem still persists. I am at a loss. Over a hundred images useless for a reason I can't fathom.

 

eiu

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aha! While the "undefined
EIU's picture
EIU
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Joined: 2011-12-20

aha! While the "undefined paramenter

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: name" problem still exists, once I redid the sequence after changing the filter code, the right magnitudes popped out of the time series. Thank god for that. Thanks again for the great advice. Glad you pointed that out before I took too many more image runs.

 

eiu

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