First, a bit of background. I am a professional Forester.
In the early 1980's Forest Service researchers starting creating modeling systems for timber harvest scheduling and other issues in forest managment. Those computer models were pretty amazing and allowed modelers expand the models to incorporate all sorts of NEW information into the computer models.
That was fine, except the building of the NEW models was expensive since the planning problem was siginifcantly expanded.
Using the NEW models with the simplier data sets, however, gave the opportunity to quickly and efficiently examine the traditional issues.
Like with any new shiny object, the Forest Service analysts went off the deep end and spent years and lots of taxpayer dollars building the new computer models. Which in the end didn't help but rather hindered resolving the political issues of National Forest management.
Back to variable star observing.
I started as a visual observer back when I was a teenager and over the years as career and circumstances allowed picked up and dropped out of visual variable star observing.
This year I finally sat down and have been trying to set up a CCD observing program. It is an adventure to learn how to incorporate darks, flat-fields, calibration routines, etc. etc. into a CCD observing program.
At the end of each new evening "adventure" I simply pulled out my old variable star charts and started revisiting my "old" visual friends with the CCD camera and V filter to see what they were up to.
I have a very good mount and a roll-off roof observatory. I could find a variable star and make a visual estimate based on what I was seeing on the screen. I could even apply my calibration flats and fairly quickly make estimate that was easily repeatable and archival since I could save the image.
Those advantages are not available to strictly visual estimates.
I really enjoyed those short sessions. The advantage was that it took less time than to find the variable than working visually, and I could see much, much fainter stars from my suburban sky with the camera than visually.
I understand the wonder of good CCD observations. The work done in the past twenty years with CCD camera really is amazing.
Oh......by the way......No variable star estimates were submitted to the database. But it was fun visiting "old" friends, some of which were too faint to see visually!!!
But my question is there room for a "lower" quality CCD variable star estimate, which is probably still better, than a strictly visual observation??
Vladimir
Please see the Observation Type "VISDIG" in https://www.aavso.org/aavso-extended-file-format and consider -- I think this might match your intended observing pattern quite well.
EDIT: I've just come across the older forum thread https://www.aavso.org/what-visual-digital-image-format in which Arne Henden warmly recommends using standard photometric software instead of visual estimated from digital images. I would have to agree, especially if using linear-format images (e.g., RAW from DSLR or FITS from CCD) rather than some inherently non-linear image format like JPEG.
Hello Vladimir,
Welcome back to the world of observing! I know that you have been a visual observer for a long time and appreaciate the fact that you are branching out into the CCD world and planning to submit your observations again.
As Eric pointed out, we have a term for what you are proposing to do: VISDIG (which stands for visual observations made from a digital image). Unfortunately, we do not encourage this kind of observation for several reasons:
- As a "hybrid" type of observation, VISDIG is neither a V-band CCD observation nor a visual observation which I like to think of as "eye" band. It therefore is of very limited use to researchers as it cannot be compared to observations submitted by others over the years.
- There are a number of potential pitfalls such as the fact that by simply looking at an image on a screen you cannot tell if the target star or any of the comparison stars are saturated. Another problem is that your screen contrast could give you a false impression of the star's relative brightness.
- The WebObs utility for uploading VISDIG observations is currently broken.
Since it sounds like you already have all the equipment and are doing the majority of the work needed to produce a good CCD image, why not take the last few steps and using VPhot software, perform the photometry and create an AAVSO report to submit which will produce much more satisfactory results?
If you are having any trouble learning the ins and outs of photometry, we have a number of resources available to help you:
- CCD CHOICE courses (which will be taught in January and February). There is also a course on VPhot itself which will be taught in September
- The AAVSO Guide to CCD Photometry
- Forums on Photometry and VPHOT to which you can post your questions. Fellow observers are very eager to help.
- As a member, you can request a mentor.
I hope this helps.
With many thanks and best regards,
Sara
Thanks Eric,
For the link to Henden's discussion on VISDIG that was helpful. Interesting that the error for VISDIG images is greater than visual. That I didn't expect. I just thought that with a visual filter that it should work out to the same accuracy as a "regular" visual measurement.
Sara, many thanks.................
for the clear explanation of VISDIG and its pitfalls. I have a much better understanding of the issues regarding VISDIG.
I really enjoyed just hopping from one variable to another and just seeing what each star was doing. It did bring back the magic of just starting out in variable star observing. I thought it might be a good "gateway" to starting variable star observing in urban areas and then progressing onto serious CCD work over time.
It has been an adventure getting into CCD variable star observing. I tried on my own, and failed a couple of times. This time, a advanced astro-imager has moved into the Wenatchee Valley and he has been helping me go through the flats, dark, substractions, etc, etc. I think with his help I will probably be able to get over the hump this time. Unfortunately, the clear skies of summer and fall have given way to the clouds of winter and very limited opportunity to observe until mid-Feb.
I will sign up for the Choice classes. I have pretty much gone through the first four chapters in the manual, but I do need the class to get comfortable with what I am doing.
Unfortunately, January is the month when I travel from Wenatchee to my "wintering" grounds outside of Tucson. I think with my previous work this summer, the info provided by the class, and taking my camera, and travel scope and mount I will be able to complete the class. I just have to make sure that I have a cell signal at the end of the travel day.
Vladimir
SVD wrote: "Interesting that the error for VISDIG images is greater than visual. That I didn't expect. "
And rightly so. That statement is doubtful. I've seen no evidence supporting it.
But more important is Arne's advice to use any standard photometric software rather than rely wholly on visually inspection. Then you can determine your VISDIG accuracy and precision for yourself.