Hi Steve and Dennis, I received the following advise from Karl Stapelfeldt, chief of NASA's Exoplanets and Stellar Astrophysics Laboratory:
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Originally Posted by Karl Stapelfeldt
Let me advise you a bit on which disks to try in the catalog. Many of them are only detected at radio or infrared wavelengths, have been tried with Hubble in visible light and not seen. You'd only be frustrated with those, so let me steer you away from them. For your equipment you need disks that are bright and large. I see that you are in New Zealand. The best targets to try for these criteria are AU Mic and HD 15115. Both are a good bit fainter than beta Pic though.
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Beta Pictoris is by far the brightest one. I don't think any of the other discs are going to be easy but they are certainly worth a try.
I got a significantly better image when using shorter exposures of only 7 and 4 seconds for Beta and Alpha respectively. I chose 7 seconds because with less exposure I didn't see any noticeable decrease in the area of saturation unless I went all the way down to something like 0.5s where I'd imagine the disk is definitely not visible. But that depends on the camera's well depth, it may be different for you. It might be worth trying 5 and 3 seconds when you have a more sensitive camera than mine.
Just remember it still has to fit with the factor of 0.59 for Alpha, so depending on how fine you can adjust the exposure times you may choose another number. I can only adjust exposure in 0.5s increments, so I had to choose something that was compatible with that
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Originally Posted by kinetic
Rolf,
I've done a few more sets on a few more nights, pretty much with no change in my imaging train.
Seeing has been better on two occasions to my initial sets. Still no result for me.
The moon is in the way now for a few weeks so I hope to use the down time to try a few things with the secondary/ spider.
You may be right about the spider vanes.
It's certainly not the primary obscured by clips, and I feel it's also not due to collimation, or collimation
change rather, due to OTA flex when slewing from Alpha to Beta.
See the attached Airy disks of out of focus stars near Sirius (low declination) and stars near the SCP (high
declination).
Almost no change.
I really want to get to the bottom of this and hopefully get a positive result from my rig.
I'm reluctant to turn the entire OTA 10 or so degrees to take the diffraction spikes further away from the PP Disk PA.
And I probably won't if the tests with an alternative spider show no
improvement.
I might even give one of the SC1.5 webcams a go too!
Also, it has been remiss of me not to apologise.
I did raise doubts, I followed them up with my own observations, and
until I get to the bottom of it, I really need to apologise for firstly
hijacking the thread, and secondly doubting your results.
I never doubted your abilities BTW Rolf, only your results.
It's also interesting the list Dennis has attached to your better result thread.
I noted the PA, inclination and angular size of a few other PP disks.
It looks like we could have some far easier targets for amateurs, based
on your result with beta Pict.
regards,
Steve |
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Originally Posted by Dennis
Hi Steve
I might select one from that list and give it a go with the Mewlon 180 if the weather ever clears in Brisbane. I haven’t had much success with Miranda, one of the fainter moons of Uranus, because of the distinct diffraction spikes from my 3-vane spider (6 spikes) and the plane of Miranda’s orbit always seems to place it on one of the vanes!
Cheers
Dennis
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