Sirius A & B - split visually and with DMK31AF ccd!
Hello,
Here is an image showing Sirius A & B from 15th January using my Mewlon 180 F12, TeleVue x4 PowerMate and DMK31AF04.AS ccd camera.
During the session, I was able to split Sirius A & B visually for the first time after a couple of years trying, using a Tak LE 5mm eyepiece. At times, when the approx 7/10 seeing allowed it, the B component could be quite easily seen as a steady and unmistakable stellar point which would hover there for 2 or 3 seconds before atmospheric scintillation returned to disturb the view in the eyepiece.
When these cells of steadier seeing did appear, it was noticeably easier to see the B component on the live image on the computer display compared to looking at the pair visually through the Tak LE 5mm eyepiece.
Turning off the RA motor was useful in determining where I should begin looking for the Pup, as it trails Sirius A as it drifts westward in the field.
Darn Den, I am still trying to see this one visually, after all these years.
I am fearful that the secondary is "obstructed" at the moment behind one of my spider vanes. I'll keep trying.
Nice shot though, very nice.
Gary
This is a excellent image. I also looked at the Hubble comparison (thankyou for the link). Do you follow the same HUbble process of over exposing the image to bring out the companion?
impressive Mr Simmons, very impressive! was the camera (from astrofest) and the technique the difference in capturing the moment, or just your skill?
Thanks Dave! Yes – I used the DMK31AF04 that I purchased at the Qld Astrofest from those nice people at Bintel. The pixels are 4.65microns compared to the 5.6micron pixels of the DMK21, so in theory, the resolution should be better?
Although the DMK31 can only record at a max of 30fps compared to the 60fps of the DMK21, a big advantage is the 1024x768 chip compared to the 640x480 of the DMK21. Getting a star on the chip at an effective focal length of 8720mm at F48 is sure easier with the DMK31 after a GoTo.
My experience from my last efforts helped me decide on more optimum settings for the split, as I think the seeing and altitude were similar. Using the x4 PowerMate also helped separate the Pup further from the glare of Sirius A.
Very nicely done Dennis. I'm wondering if you'd improve on this using the drift scanning technique...maybe worth a try some time. Thanks for sharing.
Thanks Jase - I did a Google search on drift scanning and an initial scan (pun intended) of the various resources looks very interesting.
It seems a big hit with the Minor Planet Centre and French amateur astronomers. There are some software packages that mention the ST7 and the ST8 and they all seem to caution about big files.
This site in particular looks quite comprehensive if anyone is interested.
Heck Dennis - exquisite work as always, but you've even given the Hubble a run for its money this time!!
Thanks Rob – I wish! I just love how the HST has captured the Airy disc and Airy pattern of Sirius B!
Quote:
Originally Posted by AlexN
Rob is right... thats a very very impressive result Dennis... Utterly fantastic split!
I split the trap into 5 stars with my DBK31 about a week ago in the C11 @ F/10, but it was nothing on that result of yours!
Well done indeed.
Thanks Alex – the Trap can be quite a challenge when the seeing is not so good. The Mewlon is nice 'cos its open tube design allows it to cool down quickly.
Darn Den, I am still trying to see this one visually, after all these years.
I am fearful that the secondary is "obstructed" at the moment behind one of my spider vanes. I'll keep trying.
Nice shot though, very nice.
Gary
Hi Gary
Yes – I was over the Moon when I visually split the pair. I was so very lucky to be able to have bursts of 2 or 3 seconds where Sirius B was just hanging there, a pale but very distinct dot just on the edge of the fainter, outer rings of the Airy pattern.
Keep plugging away mate – you will succeed. I found a good trick was to turn off the RA tracking of the mount (I did this in software via SkyTools so I wouldn’t loose alignment and position) to watch Sirius A drift West in the field then I knew where to look for the trailing Pup which followed the big Dog Star.
I also found I had to rotate the DMK to make sure the Pup wasn’t hiding in the diffraction patterns of the 3 vane spider.
Quote:
Originally Posted by spacezebra
This is a excellent image. I also looked at the Hubble comparison (thankyou for the link). Do you follow the same HUbble process of over exposing the image to bring out the companion?
Cheers Petra d.
Hi Petra
Thanks! Yes – Sirius A is grossly over exposed at 1/15 second. I think I once increased the exposure time to reduce the bloated appearance of Sirius A and I got up to over 1/1000 second and Sirius A was still too bright and bloated to show the Airy disc and in-focus 1st diffraction ring.
Quote:
Originally Posted by Ric
Excellent work Dennis, a very fine capture.
Cheers
Thanks Ric! I can sleep more easily now that I’ve ticked this one off the visual to-do list.
I also found I had to rotate the DMK to make sure the Pup wasn’t hiding in the diffraction patterns of the 3 vane spider.
Hi Dennis,
the leading/following I am conversant with, as Antares is similar.
Rotating the DMK has me though, I thought you would need to rotate the whole tube, or at least the upper cage area??
Gary
Hi Dennis,
the leading/following I am conversant with, as Antares is similar.
Rotating the DMK has me though, I thought you would need to rotate the whole tube, or at least the upper cage area??
Gary
Hi Gary
By rotating the DMK31AF04 from the start position through 90, 180 and 270 degrees I was able to make Sirius leave the right of the field, the bottom, left and top of the field.
I figured this was due to how the software reads out the data on the chip, one row at a time?
I’ll have to check at the ‘scope again, but from memory, with the DMK label on the face on LHS of the OTA, this is how my FOV is oriented when I move a star using the motor movement keys.
Hi Dennis,
nope, the thrust of my sarcasm, LOL, was that the orientation shouldn't change with respect to the spider vanes surely?
I feel that with my current visual failures that the vanes are impeding my views.
I'll keep going with it.
Gary
Hi Dennis,
nope, the thrust of my sarcasm, LOL, was that the orientation shouldn't change with respect to the spider vanes surely?
I feel that with my current visual failures that the vanes are impeding my views.
I'll keep going with it.
Gary
Whoops – got my knickers in a twist with that one Gary! The camera orientation change from start position -> 90 -> 180 -> 270 was to confirm that the Pup was real and not a seeing artifact, as in moments of unsteady seeing the outer (in-focus) Airy diffraction rings can break down from a continuous circle to a necklace of beads, where a detached bead could easily be confused with the fainter Pup.
Incidentally, the 3 vane spider in the Mewlon acts as a built-in Bahtinov Mask on brighter stars. It is easy to get a nice focus as one of the spider vane diffraction bars “moves” in relation to the other, two just like the Bahtinov Mask, although no where near as pronounced. I wonder if this was a conscious design decision by Takahashi?
Thanks Jeff, it was sure nice to get the visual split! The on-screen split is “relatively easy” as the view is much easier on the eye, the brightness disparity being somewhat toned down by the display gamma as compared to the much more intense visual view.
I just love how the HST has captured the Airy disc and Airy pattern of Sirius B!
