Sirius A & B - split visually and with DMK31AF ccd!

[Dennis]

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.

Here is a link to a HST image of Sirius A & B (http://www.spacetelescope.org/images/html/heic0516a.html).

Cheers

Dennis

[renormalised]

Nice piccie, Dennis.

The pup wants to bite "mum" on the ear:P:D

[Kevnool]

Thats great work again there Dennis. Its so hard visually with the flareing and the difraction spikes but alas i,m impressed....cheers Kev.

[h0ughy]

impressive Mr Simmons, very impressive! was the camera (from astrofest) and the technique the difference in capturing the moment, or just your skill?

[jase]

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.

[RobF]

Heck Dennis - exquisite work as always, but you've even given the Hubble a run for its money this time!!
:cheers:

[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! :D

Well done indeed.

[Lester]

Very nice image of a difficult object Dennis.

[gbeal]

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

[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.

[Ric]

Excellent work Dennis, a very fine capture.

Cheers

[Dennis]

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.:thumbsup:

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.:thumbsup:

Cheers

Dennis

[Dennis]

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.

http://www.driftscan.com/



Thanks Rob – I wish! :lol: I just love how the HST has captured the Airy disc and Airy pattern of Sirius B!:eyepop:



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.

Cheers

Dennis

[Dennis]

Thanks Lester!:)



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.



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.:eyepop:



Thanks Ric! I can sleep more easily now that I’ve ticked this one off the visual to-do list.:)

Cheers

Dennis

[gbeal]

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

[Dennis]

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.

-------------S
------E--------------W
-------------N

Cheers

Dennis

[gbeal]

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

[theodog]

Nice one again Dennis.

[Dennis]

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?

Cheers

Dennis

[Dennis]

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.:)

Cheers

Dennis

[atalas]

Nice work Dennis ..... and a visual split as well ! something most of us haven't managed to do.

[tonybarry]

Great effort Dennis, twenty years ago it would have been a university research project to do this.

Regards,
Tony Barry

[Dennis]

Thanks Louie and Tony!

Cheers

Dennis

[AlexN]

Congrats on Picture of the Week Dennis!

[AstroJunk]

Great work Dennis.

Here's how I get the PA with video - If I run my occultation timing device over the video stream (I use a GSTAR-EX), then I can registax align it over a number - ie a non-moving object to give the 'streak' when i stop the scope drives - I've enclosed an example I took a few weeks back. There are plenty of software packages that can overlay an image on top - webcamMax for eg. I'm sure there must be an easier method but it works for me.

I didn't do such a good job - I needed to have turned up the gain a little to get a more saturated path, but it is enough to get a reading.

The interesting thing is that my PA seems to be much closer to 90 degrees than it is predicted to be, and your estimated PA is spot-on.

If you get another chance to make a measurement, then it would be very valuable - one of my colleagues at the AAQ could make something useful from it...

Jonathan

[Dennis]

Thanks Alex and thanks to Mike and the Team for giving me my 15 minutes of fame – or should I say, 1 week of fame!:lol:

Cheers

Dennis

[Dennis]

Hi Jonathan

You’ve made easy work of splitting the Pup – well done! The GStarEX certainly seems a very versatile and capable imaging device.

I don’t follow a rigorous observing or imaging program, I’m more of a space tourist so I don’t calibrate or pre-configure my system to a baseline set up and orientation to allow me to make measurements as you do.

However, I’ll certainly give this one another go and orient the DMK aligned to the NSEW axis more rigorously, so I am better able to take some measurements. All I need now are some, well, clear skies!:)

Cheers

Dennis

[Dennis]

Hello,

As a comparison against the Mewlon 180 F12, here is a stacked image of Sirius taken through the Celestron C9.25 F10 with essentially the same set up; a TeleVue x4 PowerMate and DMK31, albeit in seeing judged to be slightly inferior, estimated at 6 to 7/10 on 7th Feb 2009.

What was really surprising, were the patterns of diffraction spikes in an SCT that only has a central obstruction, no spider vanes????

Cheers

Dennis

[AlexN]

The spikes are rather odd for an SCT.. I would have thought it would give normal round stars with a slight airy disc... ?? Oh well.. In any case, this is a good comparison, the C9.25 was still able to very clearly split the pup from sirius, although I think due to the seeing, the Mewlon image has come up trumps.. Its always good to be able to do these sorts of comparisons..

Cheers.

Alex.

[Dennis]

Hi Alex,

Until some optical or atmospheric guru can come up with a possible explanation, this one has really got me puzzled???

When I stretch the raw data using the Histogram, Gamma and Tone Map tools in Registax, the spikes really extend all the way across the 1024x760 frame?

Cheers

Dennis

[AstroJunk]

Looking good.

Out of interest, what is the spider configuration on the Mewlon?

[Dennis]

It’s a 3 vane spider on the M180.

Cheers

Dennis

[kinetic]

Pinched optics?
Main mirror or secondary?

Steve

[gbeal]

Well, dogged persistence has paid off. I cracked it visually a few nights back, and was surprised at the distance they are apart. Dim though that secondary, dim I say.

[Dennis]

Hi Steve

With the x4 PowerMate, when I defocus Sirius just inside and then outside of focus, I see nice concentric rings either side, once the tube currents have died down.

I’ll confess up front that I’m no optics genius, :lol: but I once saw a photo of pinched optics in a book and I think the diffraction patterns were more like rounded triangles?

Cheers

Dennis

[Dennis]

Hi Gary

Well done mate! You must be riding the wave of recent Kiwi successes.:thumbsup:

Cheers

Dennis

[RobF]

Hmm. I see in the latest AS&T the separation is gradually widening through until 2025 - when an 8" should be able to split them.

I've only got 16 years to go then! :P ;)

[David Tangye]

I am curious to know: is that the true diameter of Sirius you are seeing, or would it actually be say 70% that size and the atmospherics etc are 'fuzzying' its light image up bigger?

[Dennis]

Hi

Sirius A is grossly over exposed in order to bring out the much fainter Pup, Sirius B. If I set the optimum settings for Sirius A alone, it would look something more like the following example of Eta Orion, where you can see the Airy pattern.

I would probably have to expose at around 1/1000 to 1/2000 sec to avoid Sirius A from saturating and “blobbing out” to the extent it did.

Cheers

Dennis

[Dennis]

Hello,

On March 6th, I had another go at Sirius A and B with the intent of trying to make a composite of the pair, without the A component being “blown” out. I used a Celestron C9.25, Televue x4 Powermate and DMK31AF04 CCD camera, working at F40 and an effective focal length of 9400mm.

To record both A and B in the same frame, I used an exposure of 1/15 sec, which grossly over exposed the much brighter A component, but revealed the fainter Pup.
To record A as a more pleasing “dot” I reduced the exposure to 1/4000 sec which means that B was not recorded as it was too faint for such a short exposure.

I then made a composite of A (1/4000 sec) and B (1/15 sec) to more realistically show the separation between these components. I measured the distance between A and B at around 76 pixels. With an approximate image scale of 0.1 arcsec/pixel, this gives a separation of 7.6 arcsecs.

Finally, I included a single frame from the 1250 frame AVI to show what a raw, unprocessed image looks like.

Thanks for looking!

Cheers

Dennis