ATM Seeing pulsars pulse

[Bob Bond <rgb@ncube.com>]

Since I've had several private requests for detail I thought I'd explain
the project to the group as a whole.

The central star of the Crab nebula is a 16th magnitude pulsar.  It flashes
about 30 times a second with a low duty cycle pulse.  The idea is to set up
a shutter running at a speed just slightly faster or slower than the
pulsar.  The two periods will beat against each other and the star will
appear to strobe on and off.  In particular, if the shutter opens 29 times
a second, the pulsar will appear to flash on and off at the rate of once
per second.

My shutter consists of a plastic fan-blade-like device with 5 blades
mounted on a stepper motor.  I built a simple circuit from a 555 and an
SAA1027 that runs off of a 12 v battery.  The 555 is controlled with a pot
so I can ramp up the speed and adjust the rate.  The stepper is mounted on
a 2" OD tube that fits into the focuser of a dob.  The motor and blade fit
inside the upper cage so that the blade interrupts the light path into the
focuser.  The inside of the tube is the same size as a standard eyepiece.

I had some trouble with vibration and some trouble with the stepper
stalling out because it was running too fast.  We got it working well
enough to try on several different telescopes.  In particular we tried my
16", Dan Gray's 14", Chuck Dethloff's personal 24" and a 30" that Chuck was
working on.  We never had a night that the seeing was good enough and
everything was working that I could say that I saw the star strobe.  I have
my eye on Swayze's 40" and hope to try again this winter.

                                Bob

At 07:32 PM 9/22/98 +0800, you wrote:
>
>.... Well, this has been a project that I intend to have a go at very
>soon....
>what sort of aperture were you using....?????...... what were your sky
>conditions like...??????.......
>..... Regards,
>        Clive....
>
>-----Original Message-----
>From: Bob Bond <rgb@ncube.com>
>To: Taras Masnyk <tmasnyk@surgery.bsd.uchicago.edu>; atm@shore.net
><atm@shore.net>
>Date: Tuesday, September 22, 1998 3:01 AM
>Subject: Re: ATM Scavanging laser printers
>
>
>>
>>I found a very nice stepping motor in an HP inkjet printer.  I used it to
>>make a spinning shutter to use in a vain attempt to see the Crab's central
>>star strobe.  Need aperature for that one!  Got some nice machined
>>stainless steel shafts, a power supply, etc too.
>>
>> Bob
>>