Skip to main content

MaximDL Photometry with Separate Image and Reference

4 posts / 0 new
Last post
KykyElric
MaximDL Photometry with Separate Image and Reference

I currently have MaximDL 5.07. The CCD camera that my telescope uses has a limited 9 arcminute field of view, thus requiring me to take separate images of my target and reference. However, upon attempting differential photometry after calibration, I could not find a way to perform differential photometry at all on separate images. I've tried having both the target and reference images up at the same time with both labeled accordingly, but Maxim gives the error message: "Not all non-excluded images have reference stars tagged, or all images are excluded." Is there some way to get Maxim to recognize a target and reference on separate images?

Also, I've already tried using the "Add Reference Star" plug in, but my images are so small (due to the images being subframes taken to save download time) that the added reference star covers up the target.

If there is no solution to the above problem, is there another piece of software that will perform photometry with my current situation? Or, perhaps, is there a simple way to get the information I need to do the photometry myself?

File Upload: 
ritzelj
using offset and new sequences

KykyElric

My FOV is about 13 acrmin so I understand your issue.  What I have found is that I can something offset the actual FOV center so that both target and comp are within the FOV.

Also have you tried to request a new sequence for your targets?  With the new APASS database they are able to get better smaller FOV sequences then before.  This has worked well for on certain targets that even using offset coordinates still will not get the number of comps within the old sequence FOV.

Something to consider.

John R

HQA
HQA's picture
small field of view

I agree with what John has said about asking for new sequences that can sometimes help with small fields of view.  While you can use a CCD camera like a traditional single-channel photoelectric photometer, and actually use the PEP program software for the data reduction (something to consider), one of the BIG advantages to CCD observing is that you can do differential photometry inside the field of view, where all objects are imaged simultaneously.  This removes much of the atmospheric effect, and can even be used under partly cloudy sky conditions.

So how to handle a small field of view?  John mentions offsetting, so that you put the target closer to a corner and therefore effectively increase the available field for finding a comparison star.  You can use stars fainter than the target for your comparison star - as you go fainter, more and more stars will be present in your field of view.  The usual limit is about a 2.5 magnitude difference - you can push your target closer to saturation, and still get good signal/noise on the fainter comparison stars.   You can even extend that by stacking multiple short exposures so as to keep the target from saturating, while improving the signal/noise on the fainter stars.  You may need to inform the sequence team of your goal, so that they can select fainter stars for you.  An even better choice is to select your program stars to only be those with good comparisons within the 9arcmin field of view.  You might be surprised at how many targets are still available.  In other words, choose fields that suit your equipment.  I always mention EW Sct, which has a comparable-brightness star only an arcmin away from the variable, but there are thousands of such targets.  Finally, consider using a focal reducer.  I don't normally recommend them for the typical setup, but in this case they can dramatically increase your field of view and open up missed opportunities.

Arne

BPO
BPO's picture
Small fov

Hi KykyElric, regarding your imaging setup, what about using a focal reducer to increase your fov?

Log in to post comments
AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484