I expect a number of new PEP observers to become active in the coming months and they will likely have common questions to ask and experiences to report. We’ll use this thread as a container for those communications.
Tom
First thing: new observers will need an AAVSO online account and an Observer Code. It is also greatly encouraged and appreciated to become an AAVSO member. See the link below. Tom
Where can one purchase a PEP?
Peter
BPEC
Peter:
Optec no longer sells these photometers. I scrounge used ones to loan out.
Tom
I’m signed up now, observer code CMIM. The PEP is somewhere over the Pacific Ocean.
By way of introduction I am an amateur astronomer in Auckland, New Zealand. My main interest is Asteroid Occultations. I responded to Tom’s call for southern hemisphere observers and am well positioned for Antares observations.
Michael
First Steps
New PEP observers will need to get the photometer mounted on the telescope. This may require balance adjustments, for the SSP is heavy. If you have a cassegrain scope on a fork mount you will need an equatorial wedge. In alt-azimuth mode the optical tube can only be brought up to about 65 degrees altitude before the photometer case hits the base of the fork.
With the mechanical installation done, you will need to work out the best way to run the 12V power cord so that it reaches the photometer in any orientation. When operating the scope be careful not to start wrapping the cord around the mount.
With that done you are ready to start experimenting with the photometer. Try centering it on a star and see how well your mount keeps it in place. This may differ in different parts of the sky.
Next, get a handle on how far you must move the scope off-target to take sky readings. An easy way to do this is to set the integration time to one second, and with a slow slew speed move away from the star until you see the counts stop dropping. Flip the mirror and look in the eyepiece to see how far you have moved. The brighter the star, the further you must go.
At this point you should look at chapter one of the PEP observers guide (Photoelectric Photometry (PEP) Observer's Guide | aavso)
Try a single-filter sequence on one of the PEP program stars. At this time of year (May-June) you could try one of the “constant” targets, SY UMa or NSV 6687 (UMi), with V magnitudes given below. The complete target list is found in the “starparm” file (Photoelectric Targets and Data Reduction | aavso).
SY UMa 5.28, comp HD 82328 3.175, check HD 82621
NSV 6687 4.275, comp HD 136726 5.013, check HD 142105
Until you have established color calibration you will not be able to submit results - right now you are just trying to become comfortable with the steps of the sequence.
As you proceed with the sequence watch the counts. Those numbers are your best diagnostic of trouble. The counts should be fairly consistent during the sequence. It’s a particularly good idea to fix in your mind the approximate count for the first sample (comparison star) and see that subsequent comparison counts are comparable.
And I forgot to add: give your photometer time to acclimate to the outdoor temperature - at least half an hour (I try to allow 60 minutes), and let the electronics run for at least ten minutes. As the ambient temperature changes, your counts will change and this will be most apparent in the sky readings or when you have the mirror down for eyepiece viewing.
If you habve a Generation I photometer, there is a mechanically adjustable “offset” that governs how many counts take place with the mirror flipped down. A few hundred counts in ten seconds is appropriate. [The Generation II offset is harder to adjust.]
Tom
The Optec photometer arrived today. After weeks of storms and bad weather I should get a few clear nights over the weekend to start learning how to operate it.
Antares is in a good position from late evening. What comparison star should I use?
I can see Leo Minor at 18 deg elevation so could use it for practice but I don’t think I will get high quality results at that low an elevation.
Michael
Calibration and Target Stars
Information on PEP program target/comp/check stars can be found in the “starparm” file on page Photoelectric Targets and Data Reduction | aavso
The somewhat cryptic contents have, on each line, names, coordinates, V magnitudes, and B-V colors for target and comparison stars, plus names, coordinates and magnitudes for the check stars. Look for “ALF SCO” to get the Antares parameters. If you use the on-line PEPObs reduction tool you must identify your target with the starparm name and not any AAVSO synonym.
At this time of year, southern hemisphere observers will calibrate on the Centaurus red/blue pair (see Obtaining Transformation Coefficients | aavso). They transit at about 00:30 local standard time.
Tom
I had first light with the photometer tonight. Not great conditions with very high humidity and some cloud. Managed to get it all set up and had a go at the colour calibration using c1 and c2 Cen. Had to stop due to very high humidity and condensation, not that the results would have been viable anyway. But at least it all seems to work and I have figured out a basic workflow finding focus and the target stars and my tracking seems to be good enough with or without guiding. Tomorrow night should be better conditions and might be good enough for some real measurements.
Ambient Environment
Before using your photometer each night let it acclimate to the outside temperature. I like to set mine out an hour in advance. As the temperature changes the offset counts will change. As I understand it, the counts for a given photometer could go up or down as the temperature falls. Make sure your offset does not go too low. I aim for an offset count of about 40 per second during data collection. This improves linearity at the low end (though I only tested this on one unit).
Unless the temperture forecast is extreme (over 90F or under 20F) I leave the photometer attached to the telescope. However, if rain is expected I bring the photometer inside (moisture is not good for it).
Also, let the photometer run for at least ten minutes before taking data. This gives the electronics time to stabilize. I actually leave my SSP3 turned on all the time.
Tom