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Locating Faint Photometric Targets

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#1 John Downing

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Posted 19 May 2020 - 12:19 PM

I am just getting started once again, with a goal of beginning photometry. Currently using APT and have plate solving operating well with ASTAP & PS2. 

 

ASTAP has a function called Star Annotation and Photometry that looks like just what I need. But am wondering what is the best and/or recommended method of pointing to and identifying photometric targets and comparison stars? Have referred to the AAVSO CCD guide and it isn't specific (from what I can find) in this area. ASTAP identifies and provides magnitudes for comparison stars with a display that matches the AAVSO charts. Very nice if I can get it to work with APT and my mount.

 

What software and methods are photometrists using to 'go to' their targets? Is there a way to include this ASTAP function into my APT/Cartes du Ciel/CEM60 combination? 

 

My apologies if I have missed something in AAVSO publications or this forum's posts. Please refer these to me if this is the case. 

 

Thanks,

 

John

 

 

 

 



#2 StarmanDan

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Posted 21 May 2020 - 09:33 PM

My club is heavily involved in photometry and operates a .6m RC. Our scope software does not have the ability to sync on plate solved images, so We find our targets the old fashioned way, enter the target coordinates in our control software and goto it. Take image, and compare to charts provided by AAVSO or other source. Helps to have the image oriented to match the charts. Haven't had any problems finding our targets.

#3 John Downing

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Posted 22 May 2020 - 09:50 AM

Thanks Dan, 

But I was looking for an easier, softer way! cool.gif Actually, I reverted to that last night. Still a work in process as I have so much to learn. 

 

I appreciate your response and envy your .6m ota as well as your group effort contributing to science. 

 

Clear skies,

 

John



#4 Jamey L Jenkins

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Posted 22 May 2020 - 08:07 PM

Been doing photometry with a push to mount for a about a year. I print AAVSO charts to match the view of the science camera and a "finder cam" then use the slow motions on the mount to slew into position when I get close to the desired field.

 

Works but is time consuming, actually about 50-75 percent of my observing time. I've ordered a new Losmandy GM811G goto to facilitate my photometry. This should increase my productivity dramatically and decrease frustration when finding variables in star poor regions.

 

I will still output the AAVSO charts but getting to the field will be a breeze!


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#5 John Downing

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Posted 23 May 2020 - 09:24 AM

Jamey: Enjoy your new mount! It will certainly increase your productivity. I am working through how to control my CEM60 mount and other equipment with APT. This is working out very well. Last night was a breakthrough for me as I was able to efficiently use plate solving for alignment and pointing. I now understand that I can add custom objects (variable stars) which with PS will get me very close to more obscure targets. 

Clear Skies,

 

John



#6 Ed Wiley

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Posted 28 May 2020 - 12:41 PM

Back in the day I used closed loop slewing with SkyX on my Gemini-enabled G11. These days I use Sequence Generator Pro. It allows one to call up a DSS image, specify the FOV with an overlay on the image, create a slewing plan, and then plate-solves its way to the target to whatever precision you wish. I can usually center my target with two plate solves, even with a meridian flip. My mount is currently an Ap900. I have found the slews to be so accurate that I don't bother with a test image unless there is an issue with integration time.

 

My philosophy: If you are doing science you want to gather data as quickly as possible to max out the amount of data collected in a night, but if you are doing aesthetics then sit back, relax and enjoy the sky.

 

Ed


Edited by Ed Wiley, 28 May 2020 - 12:42 PM.


#7 John Downing

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Posted 28 May 2020 - 04:10 PM

Thanks Ed. I appreciate your input especially regarding using plate solving to locate photometric targets. Only a few months ago I didn't know ps was available to amateurs, but I was advised via CN that this was a must have tool for the future.

 

Since then I have tested three sequencing/control programs but had to pass over SGP due to a problem with older SBIG cameras. A problem that has recently been corrected thanks to a fellow AAVSO member in France. So, it is also helpful to know you are using SGP with good results particularly for meridian flips. I have been using APT the past few weeks and have psolving working very well. But I worry about the sequence programming and a few other factors. I need to take a second look at SGP. 

 

Am ready to start learning how to collect data and will start next week.

 

John



#8 Ed Wiley

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Posted 29 May 2020 - 09:31 AM

John:

SGP does have its limitations. This is mostly due to the fact that it is designed for astrophotography rather than photometry. For example, if I want to do three sequential runs of M67 for BVRI, I have to program in M67 three times (M67-1, M67-1, M67-3) rather than simply telling the program to recycle. Fortunately, it is easy to do the replication. Also, you must watch the options for repeating within a single target plan. Finishing all filters is the default (BBB, VVV, etc) while we photometrists would cycle between filters (BVBVBV, etc). At least once I forgot to change that option and ended up with a four hour run of "B." Again, SGP is designed for AP so you need to work with it a bit.

 

I find SGP's target generating plan, plate solving and PhD2 integration handy enough to override the above limitations(and perhaps others). Further, the cost/benefit ratio is outstanding. On a typical night I:

(1) slew the scope from park to one hour west of the meridian.

(2) plate solve to insure that the mount know where it is in the sky. (Is this really needed? I consider it a sanity check.)

(3) open and check PhD2 for tracking and adjust if needed.

(4) Get an approximate focus and then run the focus routine.

 

One tip: For the centering routine do not try to center to the nearest pixel. SGP will try to do that, but it will take many plate solves. I would have to check, but I think mine is set on 50 pixels as "good enough." As I use VPhot and LesvePhotometry, both of which plate solve each image, I don't worry about aligning images.

 

Since most of my runs are on EBs and are typically 3-4 hours I take the time to center the target and re-check PhD for guiding. Then I begin the run. After initially staying up all night I found the routine safe enough to hit the hay as SGP automatically stops PhD2,  parks the scope and warms the camera. As it directly communicates with our weather station I don't worry about the weather as all will be shut down if needed.

 

Ed



#9 John Downing

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Posted 30 May 2020 - 12:24 PM

I appreciate the benefit of your experience Ed, and the time you have taken to explain. As I consider which program to use to control equipment and sequence activities it is very helpful and reassuring to have someone experienced in photometry weigh in. Right now I am getting a heavy and early dose of what we here in SoCal refer to as June Gloom (heavy marine layer clouds) which will give me the time to become reacquainted with SGP. Your previous posts now reside in my SGP notes file for future reference.

Thanks again,

John



#10 555aaa

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Posted 30 June 2020 - 11:37 PM

I use (alterntely) MPO Canopus and AstroImageJ to figure out which star is the target and to collect the comparison stars. MPO Canopus is pretty full featured and was designed to do asteroid photometry and light curves. AstroimageJ requires a fair amount of manual reduction and doesn't have it's own photometric catalog to give you an ensemble, you have to manually go find the AAVSO comparison stars on the image (by using their coordinates) and then make a little spreadsheet, which is time consuming.



#11 Ed Wiley

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Posted 03 July 2020 - 10:51 PM

I also used MPO Canopus for several tasks and have done so for years. However, I could not get it to run on Win10, others have had better luck, probably because they are more handy with computers. So, I have a Win7Pro computer that I use to run MPO Canopus and other programs I find useful and which do not run on Win10 (or do run but I can't figure it out). Canopus simply does thing other program do not do and it does this quickly and efficiently. Brian Warner has real tutorials that guide you through the process. MPO Canopus is not the easiest program to learn but its features warrant the effort..

 

AIJ: I have adopted this one for my general image reduction. I store all frames in a single folder by image variable and night. So each folder contains a file of science images, a file of darks, a file of bias, and a file of flats. (If you have more than one image folder because you images several targets, you can clone the calibration frames or the master calibration frames such that all raw science frames are stored with calibrated science frames and the calibration frames used to do the calibration. That way there is never a question as to what frames were used to produce the science images. Given cheap storage these days I figured this was the way to go. I don't use the other features of AIJ as I don't do exoplanets, but I like the idea of keeping every thing in one folder even if it does results in duplication of calibration frames. AIJ encourages this.

 

That said, you are a lot more efficient if you insure that you actually acquire the target and that is where the plate solving approach works for me.

 

Ed


Edited by Ed Wiley, 03 July 2020 - 11:03 PM.


#12 John Downing

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Posted 05 July 2020 - 04:26 PM

Thanks for the update Ed. Glad you were able to locate a Win7 computer. I recently remembered that my old laptop runs on 7. I was going to retire it as the keyboard has some dead spots. Am going to see if I can get that fixedand run MPO on it as you are doing. 

 

Plate solving: This was my primary worry as I got started and turned out to be so easy. My plate solving, using APT/Point Craft (ASTAP & PS2), has worked like a charm from the start. It is still amazing to me that I can easily precisely locate a faint variable within minutes of startup. Just plate solve & sync, correct to center coordinates, compare to the AAVSO chart, and there it is. My thanks to all the people who offered their advice and support in this endeavor. 

 

Now I just have to master calibration, registration, and learn how to use MPO. I purchased Brian's book on photometry with MPO and have been studying that and the MPO tutorials. Can't wait to get back home, set my equipment up and start imaging again. Camping in the forest isn't conducive to astronomy. But it sure is beautiful here: Virginia Lakes, Eastern Sierra Mountains near Bridgeport, CA. 

 

John



#13 DEnc

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Posted 09 July 2020 - 05:13 PM

 

Now I just have to master calibration, registration, and learn how to use MPO. I purchased Brian's book on photometry with MPO and have been studying that and the MPO tutorials.

 

 

+1 on the software and the book.  I suspect you're going to really enjoy using these resources.

 

Another great feature of MPO is that you can import stars to the User catalog. 

 

For photometric calibration, you can download Landolt fields from https://www.aavso.or...s/vsd/stdfields, filter out any individual stars that don’t meet your criteria (e.g., magnitude), get the rest into the User catalog, and then they’re ready to use with any of the MPO widgets you like.  The downloaded list is great for session planning too, when you want to image calibration fields.

 

I’ve been working on the Delta Scuti variables with MPO, and I’ve got a good light curve down to a delta V of 0.15 (V0608 Peg).  I’m still waiting for an opportunity to image some exoplanet transits—life in coastal SoCal does make it tough!

 

David



#14 Ed Wiley

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Posted 09 July 2020 - 07:39 PM

There are two easy ways to identify AAVSO Comp stars for differential photometry.

1. If a member of AAVSO, use VPhot. It pinpoints your images and throws up the calibration stars and any variables in your FOV on the image. You can save your favorite set of comps and check for the next time.

2. LesvePhotometry. Closely integrated with AAVSO data. It is free, but is most efficient if you have a stand-alone PinPoint ($150). I have not tried the Astrometry.net function since I have (and value) my PinPoint. Again, you can save your comps and check.

 

LesvePhotometry has the advantage of being able to perform ensemble photometry on time series of multiple image of the same target. Since I like to do a minimum of 4 images of a variable (or 80-120 of an eclipsing binary), I find LesvePhotometry invaluable.

 

Given that, if you know your comp stars or like to roll your own, MPO Canopus has the advantage of not requiring a check star, similar to AIJ. SInce MPO Canopus is "asteroid-centric" this is entirely reasonable and the program has innovative features for picking comps that should keep you out of trouble wither either variables of asteroids.I use it for certain eclipsing binaries because it output files that can be used on Peranso and Binary Maker 2. It also does ensemble photometry and you can work through the transformation routines to introduce transforming your data.

 

Ed




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