Mon, 05/24/2021 - 12:40
Hello! An interesting error with the exposure time in he FITS header when the image is uploaded to VPHOT.
I imaged X HER in V filter at one second with multiple exposures and stacking. The FITS Header listed the exposure as '1' in both final stacked image and the individual image.
When I uploaded the final image to VPHOT, I had an error in the FITS header exposure time. When I edited the FITS header was '1.0,' it uploaded without difficulty. Best regards.
Mike
Mike:
Not sure exactly what your question is?
Typically, raw images that are being stacked will have the same exposure (e.g., 1 second each x ten images). The final stacked image (mean or median) would also have the same exposure (1 second = 10 seconds / 10). Arithmetically, it should not be necessary that they be the same but not sure what happens when median stack is used?
Based on what you posted, you stacked your images offline with some software. (Why not let vphot do the stacking?) You implied that the EXPOSURE header of your stacked image had 1 as the value. You stated that the exposure reported in vphot was incorrect. What was it? Was it the exposure time reported in your image list? you then mentioned editing the EXPOSURE of your stacked image to 1.0 and it was reported correctly. This would imply some arithmetic and rounding/truncation issue in vphot?
From a separate forum post, you seem to be using different (not all the same) exposures in your set of raw images for stacking?
Please provide some additional info. Share the images to MZK and SGEO.
Ken
Hello! My apologies. This was not a question but an observation of an error that I thought was curious, that is, that VPHOT required that exposure in the FITS header to be "1.0" rather than "1" after stacking 15 one-second images.
I've stacked other images under 10 seconds integration time in order to have the final image have a total integration time over 10 seconds, and I've not experienced this error before. I may have stacked other 1-second images int he past as well and not received this error, but I cannot remember that specifically at this time
My other unstacked images typically use integers, like "10" for a 10-second integration time, so I thought inability to use "1" in the FITS header was was curious.
My question in the photometry forum that you referenced was whether photometry itself would be skewed or have an unanticipated bias if images of different integrations times were stacked regardless whether VPHOT (or any other photometry software) would analyze it. Best regards.
Mike
Mike:
Could you copy and paste the specific image header with the "1" in the exposure header value into a reply post? Is there an extraneous blank character in the header value by mistake? I'm looking for one of my images with a one second exposure to confirm your observation.
What imaging software do you use? My Maxim writes the exposure header values in scientific notation like EXPOSURE = 2.00000000000E+001 / [sec] Duration of exposure.
Ken
Hello! I use MPO Canopus for image processing and photometry. Occasionally, it does not plate solve an image, and for those, VPHOT often will plate solve..
X HER in V Filter with the integration time of '1.0' is in my VPHOT file. I'll give you access so that you can view the FITS header directly.
Below is the FITS header as I copied it from Canopus. The only caveat is that when I open the FITS header in AIP4WIN, the values are enclosed in single quotation marks. I'm not sure if that makes a difference.
I tried to upload the original image to VPHOT again. When I do Quick Upload, nothing shows up. When I go through the 3-step wizard, the last screen says that there is an exposure error. Best regards.
Mike
Header Information for: X HER_1sec_V_0001_-5C_P_HeaderInfo.TXT
--------------------------------------------------------------------------------
SIMPLE = T / MPO Connections
BITPIX = 16
NAXIS = 2
NAXIS1 = 765
NAXIS2 = 510
BZERO = 3.276800E+004
BSCALE = 1.000000E+000
OBJECT = 'X HER'
TELESCOP= 'POTH (Plain Old Telescope Handset)'
INSTRUME= 'SBIG ST-402 CCD Camera'
OBSERVER= 'Michael A. Heald'
SITELONG= '-106 44 45.470'
SITELAT = '32 22 57.940'
DATE-OBS= '2021-05-24T05:24:49.179' / UT date/time exposure start
TIME-OBS= '05:24:49.179' / UT time exposure start
EXPTIME = 1
EXPOSURE= 1
MIDJDOBS= 2.45935872557E+06
OBJCTRA = '16 02 08.659'
OBJCTDEC= '+47 11 04.878'
CENTALT = '66.2352777777778'
AIRMASS = 1.093
IMAGETYP= 'LIGHT'
XBINNING= 1
YBINNING= 1
XPIXSZ = 9.00
YPIXSZ = 9.00
XORGSUBF= 0
YORGSUBF= 0
EGAIN = 0.00
CCD-TEMP= -5.2
SET-TEMP= -5.0
FILTER = 'V'
APTDIA = 0.000
APTAREA = 0.000
FOCALLEN= 1260.000
CBLACK = 100
CWHITE = 18924
PEDESTAL= 0
DATAMAX = 0
SNAPSHOT= 0
SBSTDVER= 'SBSTDVER'
UT = '05:24:49.179'
SNAPSHOT= 14
HISTORY Stack (Average)
HISTORY Image 1 Exposure: 1.000
HISTORY Image 2 Exposure: 1.000
HISTORY Image 3 Exposure: 1.000
HISTORY Image 4 Exposure: 1.000
HISTORY Image 5 Exposure: 1.000
HISTORY Image 6 Exposure: 1.000
HISTORY Image 7 Exposure: 1.000
HISTORY Image 8 Exposure: 1.000
HISTORY Image 9 Exposure: 1.000
HISTORY Image 10 Exposure: 1.000
HISTORY Image 11 Exposure: 1.000
HISTORY Image 12 Exposure: 1.000
HISTORY Image 13 Exposure: 1.000
HISTORY Image 14 Exposure: 1.000
END
It's possible VPhot will throw an error if the exposure time is "1".
It is expecting a float.
What is the exact error message that you saw?
And please send the file that is having this problem to me (gsilvis@aavso.org)
I'll look into the problem.
George
Hello! After using the upload wizard, step 1 is to select the scope, step 2 is to upload the image, and at step 3, the FITS header comes up with the note "invalid or missing exposure time (EXPTIME or EXPOSURE). Cannot continue."
I'll share the VPHOT image with you that uploaded. The Dropbox link to the image that did not load is
https://www.dropbox.com/s/04vk03ree6yolzr/X%20HER_1sec_V_0001_-5C_P.FIT?dl=0
Best regards.
Mike
I have reported the exact same error, my uploaded image receives the "invalid or missing exposure time (EXPTIME or EXPOSURE). Cannot continue." message simply because the listed EXPOSURE or EXPTIME in the header is a perfectly FITs valid single digit. In my case uploading an image with 'EXPOSURE=5.0' works but with 'EXPOSURE=5' gets the "invalid or missing exposure time (EXPTIME or EXPOSURE). Cannot continue." error.
Still waiting for the fix as I have about 300 5-second images to process, too many to edit by hand.
Regards
Stephen
Stephen,
Sign into VPhot and try submitting a fits file with that integer exposure time that has been causing problems.
It should now be okay.
If so, carry on and upload your 300.
If not, tell me!
George