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Plate solving missing on an image - what to do

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RGN
Plate solving missing on an image - what to do

I am unable to get an image of T CAS in Ic plate solved by VPHOT. All the other images have been correctly plate solved. What shall I do to use the sequence of stars I have saved for T CAS in V, to transform the observations? I can manually enter the sequence but I cannot use the same file name to save the sequence hence unable to do the transformation.

Thank you

Gianluca

MZK
MZK's picture
Revise Sequence

Hi Gianluca:

1. Best to use astrometry.net to plate-solve the I image from your computer, and then upload it to VPhot again. (Delete the old one first). Once in a while, pinpoint will not plate solve and astrometry.net will, since it is a little more robust.

2. Without a plate-solution on the I image, a sequence created manually on that image won't help since comps have no RA/Dec.

3, Once in a while a sequence created in one filter will not work on another filter image because the comps or check may not be visible in it for unexpected reasons. I often open the V sequence on the I image and correct the problem (e.g., missing check?) and save the sequence as, for example, T Cas Rev1. This corrected sequence is likely to work on both filter images. You can delete the original V sequence then.

HTH, Ken 

SGEO
SGEO's picture
Coping with VPhot not solving your I images

Shooting the LPV's I often find that the I filter will not solve: target too bright and the comps barely visibile.

I use Maxim for imaging. Other packages should have similar capability: I align all the I shots and include one V image in the alignment group. VPhot will let you share a WCS, plate solving, solution to other images: select all the unsolved I's and the the V and select the Update WCS option: you will then have them all declared solved.

Other options are also before you get to VPhot: align/stack the I images.

George

FJQ
FJQ's picture
Plate Solve

Like George, I use Maxim DL (V5.23).  I only use Vphoto to get instrumental magnitudes of either M67 or NGC 7790 for computation of transform coefficients.  However, I usually forget to plate solve them (using Pinpoint (Engine V5.1.8) and Vphot fails to solve the images.  Once I go back to plate solve the images and save them in Maxim, Vphot works fine.  As mentioned above, sometimes images are underexposed relative to the object so plate solve may fail.  To combate this, I've saved various templates in Vphot and also eliminate stars that would have overlap with the the apeture annulas as seen in Vphot.  Once you get the hang of it, you wont really need to change any settings unless you vary your instrumentation; i.e. using different focal length instruments and/or deeper exposures.

James

TRE
TRE's picture
Plate solve T CAS

Is it something simple like:

Does that image of T CAS have the correct RA/DEC in it's FITS header file? If not, change it. Then try the solve again. Works in MaxIM, maybe it will work in VPHOT.

Ray

RGN
Problem solved

Thank you all for the reply.

I followed Geroge's instructions by creating an "I" file with an average of I and one V image with Maxim DL. That was correctly plate solved by VPHOT. I then selected the Update WCS option in VPHOT and everything went right. By the way T CAS in Ic is very bright (around mag. 3)

Cheers

Gianluca

RGN
Problem solved

Thank you all for the reply.

I followed Geroge's instructions by creating an "I" file with an average of I and one V image with Maxim DL. That was correctly plate solved by VPHOT. I then selected the Update WCS option in VPHOT and everything went right. By the way T CAS in Ic is very bright (around mag. 3)

Cheers

Gianluca

HQA
HQA's picture
T Cas at Ic

Hi Gianluca,

Yep - most LPVs are extremely bright at Ic.  This makes it difficult to find appropriate comparison stars, of course, and you have to be careful about your exposure times.  I often use an exposure time that doesn't saturate the target, and then stack many subframes to achieve a decent signal/noise on the comparison stars.  You also may have to select different comps for Ic than you do for V.  It takes a while to figure out the best way to observe!

Arne

RGN
T CAS at Ic

Hi Arne,

I agree. It is a good hint to take exposures at Ic avoinding saturation of the target and to stack many subs to get decent SNR of the comps particularly if they are much dimmer than the primary target. That is what I am trying to do with my photometry in Ic.

Gianluca

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