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Photoelectric Photometry of Variable Stars - Past and Present

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#1 Rustler46

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Posted 15 November 2020 - 12:14 PM

Someone on the Classic Telescopes forum asked me to share what I called "another story" of my experience with photoelectric photometry (PEP) of variable stars. I hope this article will encourage others to make such contributions to scientific studies of variable stars. So what follows will largely be what I remember about my experience as a photoelectric photometrist back in 1985-90. Many of the concepts and techniques are still valid today. You'll find technology has improved greatly since 1990.

Click here to view the article


Edited by Rustler46, 15 November 2020 - 08:43 PM.

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#2 jcruse64

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Posted 17 November 2020 - 08:01 PM

Thanks again for posting your experiences with this. Very interesting!


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#3 Rustler46

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Posted 18 November 2020 - 02:08 AM

I'm glad you enjoyed my writeup, Joe. I found it fascinating back in the day. I may get back into it in a limited way. Maybe my AT115EDT refractor with ZWO ASI290MC can be employed. I would not want to spend much money for needed software, since it would just be an occasional exercise. I do intend to keep my yearly license for SharpCap Pro. That is 10 pounds well spent. Perhaps it has a variable star utility. If not there may be free or inexpensive software that could be used. Any ideas?

 

Best Regards,

Russ


Edited by Rustler46, 18 November 2020 - 02:09 AM.


#4 Starsareus

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Posted 22 November 2020 - 09:34 PM

Talk about "timely." I collected a number of PMTs and bones of a Starlight-1. More curious, I'd like to also try to remake one of these. Have a few Books as well (Russell Genet's, Jeff Hopkin's)



#5 Rustler46

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Posted 22 November 2020 - 10:28 PM

Talk about "timely." I collected a number of PMTs and bones of a Starlight-1. More curious, I'd like to also try to remake one of these. Have a few Books as well (Russell Genet's, Jeff Hopkin's)

That sounds exciting. If I can be of any help, let me know. I'll look in my things to see if there is any written material that could be of use in your project. I have many pages of written (snail-mail) communication of that era.

 

As I recall the counter I made had some commercial sub-assemblies inside:

  • Amplifier-discriminator
  • Counter
  • LED digit display driver.

I just wired everything together, made the holes and cutouts in the aluminum project box. And it all worked without me knowing a whole lot about the specific circuit design. While I do have an electronics and physics background, I never worked in that field. In contrast Jeff was an electrical engineer with RCA. So he knew his stuff.

 

The HV power supply was home-made following instructions provided by Jeff Hopkins. It involved winding a small toroid-choke transformer on a very small bobbin with tiny gauge magnet wire. Hopkins provided a bare printed circuit board made for the purpose. I just soldered components on the board. My coil would never produce more than 750 volts, which limited now faint a star I could measure. So Jeff allowed me to trade in my home built unit for a working one he had for sale. This would give the required 1000 VDC. Jeff was most kind to me, patiently helping me get going in PEP. Sadly, someone said he has since died.

 

Keep us posted as to your progress.

 

Russ


Edited by Rustler46, 23 November 2020 - 08:06 PM.

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#6 photoracer18

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Posted 26 November 2020 - 04:27 PM

In my case when I was a junior in HS (1964) I was looking around for a senior science fair project in astronomy and building a working amateur stellar photometer seemed like a good one at the time. At first my advisor and I had problems because there were no PMTs out commercially and that was the only possible direction. However about that time RCA brought out the commercial version of the IP21 the 931A and my father who had retired from the USAF the year before was working for a defense contractor and he managed to get me one. We built the entire circuitry from scratch based on the factory data sheets and some other circuitry we tried earlier. I was never so happy as when we had everything completed and started getting meter readings when it was mounted on my RV-6 and had a star in the center of the field. I had solved the tracking issue by adding a slow motion control to the DEC axis. I did it as more of a feasibility study since I was not involved with the AAVSO at the time, as I was more into astrophysics at the time. I donated the complete system to the school after the state science fair in 65.


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#7 Rustler46

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Posted 26 November 2020 - 04:46 PM

In my case when I was a junior in HS (1964) I was looking around for a senior science fair project in astronomy and building a working amateur stellar photometer seemed like a good one at the time. At first my advisor and I had problems because there were no PMTs out commercially and that was the only possible direction. However about that time RCA brought out the commercial version of the IP21 the 931A and my father who had retired from the USAF the year before was working for a defense contractor and he managed to get me one. We built the entire circuitry from scratch based on the factory data sheets and some other circuitry we tried earlier. I was never so happy as when we had everything completed and started getting meter readings when it was mounted on my RV-6 and had a star in the center of the field. I had solved the tracking issue by adding a slow motion control to the DEC axis. I did it as more of a feasibility study since I was not involved with the AAVSO at the time, as I was more into astrophysics at the time. I donated the complete system to the school after the state science fair in 65.

Thanks for your comment, photoracer18. We are about the same age. I was a senior in 1964. But it was few years later when I got into variable star observing, first visual, then DC PEP, finally with the photo-counting rig. I ended up donating all my PEP gear to Humboldt State College in California. Great fun while it lasted.

 

Best Regards,

Russ



#8 noisejammer

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Posted 29 November 2020 - 12:58 AM

An interesting recollection indeed. During my junior year, I had use of a 12" Tinsley. One of the boxes contained a PMT and pulse counter but no one - at least among the active amateurs at the time - could recall who had used it.

In the fullness of time, I joined the Center for Backyard Astrophysics and made many thousands of high cadence measurements of several cataclysmic variables. Targets were chosen so that they were near opposition allowing 800 - 900 measurements to be made per night and with sites around the world, near continuous coverage was possible.

Using my 12", I could usually do better that ±2 mmag, at least to ~15m with 28 seconds integration... the missing 2 seconds was to download the 640x480 image through the printer port. How times have changed. lol.gif
I discovered that an AO-7 (early SBIG adaptive optics unit) allowed the system to be extended down to near 17m (with up to 2 minutes integration.) On brighter stars, noise floors could approach 1 mmag.

Needless to say, the capture, calibration and data extraction from so many images took a fair bit of automation. This was aided by code include in Richard Berry & Jim Burnell's book, the Handbook of Astronomical Image Processing. Sadly, this is one of the treasures that has disappeared along with Willman-Bell.



#9 Rustler46

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Posted 29 November 2020 - 01:39 AM

I found a sales slip for a book I used to have Astronomical Photometry by Hendon & Kaitchuck. But I was passed on to Humboldt State University along with my photometry gear. I do still have John Percy's The study of variable stars using small telescopes. It has extensive chapters on PEP. 

 

At one point I was interested in digital capture of the photometer counts. There was some sort of digital output channel in my pulse counter. But I never felt like mastering what was needed to make that work. So writing down 7 numbers every 10 seconds along with the time became my method of operation. At the end of each month transcribing the data onto floppy discs for AAVSO processing took a bit of time. There were so many stars that the scientists would like having data on. Fascinating work! I believe for AAVSO my total was around 850 observations. But there were some other non-AAVSO programs that had my contributions. 




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