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How to Edit Comp Sequence?

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msheald
How to Edit Comp Sequence?

Hello! I am trying to edit the Comp sequence for U HER, but the changes are not saved after I edit the sequence and save it. The reason I am editing the sequence is because only 1 of the 3 comp stars are loaded when I ask VPHOT to load the AAVSO comp stars. Ken, I shared the U HER image with you.)

    I have downloaded the sequence for U HER. The target and the 119 comp star loaded when I asked VPHOT to load AAVSO comps from the catalogs drop down list. Comps 132 and 136 did not load, and I am not sure why (they are visible on the image).

    In any case, I thought that I would add them manually to the sequence. I clicked on the stars, and edited the names, comp/check status, and then put the B,V,I magnitudes in from the VSP photometry table by clicking on "Edit Sequence" from the list that comes up when I click on the star in the image. I "updated" the information and then saved the sequence.

    Unfortunately, when I tried to apply the sequence to the U HER image, the information I input does not appear - only the target and the 119 comp

    I am doing something wrong. I would appreciate help helping me to find out -

1) Why the AAVSO comps are not loaded when I click on "Load AAVSO Comps" from the "Catalogs" drop down menu, and

2) Why manualy input information does not saved.

    Thank you and best regards.

Mike

spp
spp's picture
How to Edit Comp Sequence?

Mike,

Ken probably already has the answer for you, but I'd like take a look at this also.  Please share your U Her image with me (SPP). 

Phil

msheald
Shared - How to Edit Comp Sequence

Hello! I just shared the image with you. Thank you for your help and best regards.

Mike

spp
spp's picture
U Her

Hi Mike,

In the images you shared there is one image of U Her.  This was made with an I filter.  I think the problem you are having is probably the result of trying to do I filter photometry on a Mira star with comps that are just too faint in the I filter.  

In your I filtered image the 132 comp star has a SNR of 12 and the 136 star has an SNR of 14.  This is with a 3 pixel measuring aperture radius which is a bit small for measuring the target (SNR 740).  If you enlarged the measuring aperture to a more appropriate size for the target the SNR's in 132 and 136 would be even smaller.

I suspect the reason your edits of the sequence don't "take" is that VPhot probably has a higher SNR limit set for comps .  I'd be interested to see Ken's comments on this.  Do you have the same problems with your V and B images of U Her?

Even if the edits worked, I think it is not good policy to use comps which are 6 or 7 magnitudes fainter than the target.   Your recent measurement makes U Her = 5.21 Ic.  The comp sequence information shows 132 = 11.305 Ic and 136  = 12.64 Ic .

I am happy to see you are working with VPhot, and I hope you keep at it.  I look forward to seeing you in Las Cruces.

Phil

 

 

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msheald
U HER

That's it! Thank you for your guidance.

    When I lower the SNR thresshold in settings, the comps appear when I ask VPHOT to load the AAVSO comps.

   I would like to use 132 as the check star.and 119 as the comp star. Absent the check star, VPHOT won't perform photometry on U HER.

    With the narrow FOV of my system, there aren't any other stars of comparable magnitude to the target. If I increase the exposure in I to get better SNR of the comps, the target saturates.

    So, not a great solution, since the uncertainty in I band increases with the check and comp star being much dimmer that the target, but at least I won't have to defer I-band measurements when I perform V and B on U HER.

    The only other solution that I can think of is to slew to a close comp that is of comparable magnitude to U HER in I and image that. It would be in a separate image, but hopefully the air mass difference would be negligible (and hopefully, the cloud cover, etc., would be the same between the images!). This seems similar to all-sky photometry, which I do not have any experience with, so I am hesitant to try it.

    Thank you again for our guidance. I appreciate it. Best regars.

Mike

 

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