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Variable Star not in Field

robinriordan
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Joined: 2011-03-02

I am trying to process some stars in Boo and VPHOT is having a problem. For example, RT Boo. The image uploads fine. RT Boo is right in the middle of the image. VPHOT successfully processes the WCS. No errors. I click in Variable star index and get a report that there are no variable stars in the field. I attempt to load the comp stars and message says that there are no comp stars in the V band. There are about 12 comp stars on the the AAVSO chart. This problem has occurred many times before. At first I just thought it was me. Now, I begin to suspect more is going on. Any experience with this issue?
Thanks,
Robin (RROA)

Please share your VPHOT images to KTC
KTC
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Please share your VPHOT images to KTC

Variable star not in field
robinriordan
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Joined: 2011-03-02

Hi KTC,

I am sending two images of RT Boo: calibrated, and uncalibrated.

FITS image feedback
KTC
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FITS image feedback

Uncalibrated image is a 32-bit floating point file...which is overkill because it's only the 16-bit integer information from the camera.  Configure your software to save the camera images as 16-bit.  (And if you do not stack images...you can probably save the calibrated images as 16-bit also...to save disk space and bandwidth requirements.)

Image is not in focus, and shows collimation error (star size/FWHM is larger on one side of image compared to other).  It may also show trefoil astigmatism...may need to investigate optics support/pinching problems.

Raw image histogram shows min ADU 2676, max 29044.  Calibrated image shows min ADU -7692, max 16006.  You have calibration issues...dark frame, etc.  With a large number of negative pixels...Geir and VPHOT will probably freak out when trying to plate solve.

Feel free to send me your calibration frames:  master dark, master bias, master flat, individual dark, individial bias, individual flat.

Your raw and calibrated file FITS headers lack information on:

- RA / Dec

- object name

- filter

- air mass

...VPHOT can not plate solve your images, and can't assign a filter name.  Do you manually provide that information when you upload files to VPHOT?  If you have these images already uploaded into VPHOT, could you please share them to my KTC account?

Your image is centered on the target.  But your FOV is not very large (about 21 x 16 arc minutes), and this is the star-poor spring sky.  I recommend you use planetarium software (that can display your CCD field of view on the sky), look at suitable comp stars, and adjust your pointing accordingly.  (I recommend you point midway between RT Boo and the comp 114.)  All comps in your image (except one) are fainter than the target...which is not good for CCD photometry.

Were all these issues known to you before, or is this new news to you?

How automated is your rig?  How can we improve it?

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484