Tuesday, June 16, 2020

imaged NGC 6520 at last (Bradford)

Paused my visual observing. 
Instrument: Celestron 8-inch SCT
Mount: Vixen Super Polaris
Method: slewing and tracking with IDEA GoToStar
Disconnected. Reconnected. I had just over an hour before the window closed. Slewed to Vega. It was 1/4 of a field away in the finder. Centred. Close enough.

Attached the camera. Got into Backyard EOS. Made a note to get a Bahtinov mask for the next time. Used HFD. Down to 6.4, 6.2, 6.0. OK. Set up the image filename prefix.

Vega in colour

12:20 AM. Imaged Vega for 20 seconds at ISO 1600. A couple of shots. North is left, east is down.

By the way, the B and E companions of H 5 39 or α (alpha) Lyrae as easily spotted, flanking, right and left respectively. Curiously, B is brighter than E. SkyTools shows B as dimmer in the chart, at mag 10.6; in the Object Information box, both B and E are listed at 9.5. None of that is right. 

I think I can see the third companion, C, to the 2 o'clock position from the bright star. But it is incredibly dim. ST3P says it is mag 11.0. Doesn't look like that to me.

And the vertically oriented double on the right, that's H 4 59 or PPM 81552.

Also in the image, near the top-left, is the dim double of ES 2571.

Very curious artefact around the brilliant blue-white star. Looks like a spider. Is that a representation of my collimation, collimation being slightly off?

And, incredibly, there's a halo!

Disconnected. Reconnected. Slewed to the object to see where it was in relation to the gap. In the trees. 

Did the trick I developed yesterday, of hanging something heavy on the south wall of the tent, to make a clear sight-line for the finder scope. 

Could see some stars. Readied to ID the stars. When SkyTools crashed. The looping error! Whiskey tango foxtrot, what caused this nasty error?! Bad timing. Issued a kill process. Restarted SkyTools, seemed OK after the big crash. Checked the atlas for the blinking X. Close. OK, where were we? 

Saw a bright star in the finder. Panned a bit and tried a shot.

12:33. Imaged an orange star. 25 seconds, ISO 1600 and 3200.

12:45. I heard, to the south, yipping sounds. What?! Coyotes? Packs of wild dogs? So weird... Was it real? Moved from east to west. Very strange.

Frustrated, I just aimed blindly where I thought the cluster might be and opened the shutter. Remarkably, I got it! I did not dare pan...

1:08. Look at that! Imaged NGC 6520. 25 seconds, ISO 3200. Kept shooting for another 4 minutes until it faded behind the next tree. North is left, east is down.

portion of open cluster NGC 6520 in colour

The image is centred on the star HD 164562. It's a very tight double... Wishful thinking that I can split them... 3.3 airmasses! Dimmed by 1.5 magnitudes...

I was happy, elated really. This was a key moment, a remarkable milestone, imaging the final Finest. NGC 6520. And while it was not a telescope operated remotely through social media, certainly this was a computer-driven mount and a remotely controlled camera. Also, I could tell it was not a great image but I didn't care. It was there. It was obvious.

1:15. The window closed. Wow. I felt relieved. 

With the camera connected, I thought I might as well shoot a few more interesting things...

double star BU 243 in colour

1:27. Slewed to M20 in the software. Couldn't see anything obvious in the 25 second exposure. Figured it out. HD 165594 was in the wide pair at the top of the image. 

[ed: Identified the field in Sagittarius manually. Actually, I was 1-3/4 degrees from the centre of Messier 20, at a position angle of 57 or north-east. In the image, north is left, east is down. Orange star PPM 733712 is near the centre. I actually caught the double star HD 165689 aka BU 243 with the obvious white and blue-white stars, the A and C components.]

[ed: That really bright orange star up and right of centre is VX Sgr. It's a very interesting variable star. Looks like I caught it at top brightness. From SkyTools: mag range V6.52 to 14.00 at a period of 732 days.]

1:34. Closed the north door to block light.

mu Sagittari in colour - 25 sec

1:38. Imaged the double star μ (mu) Sgr. Between 25 seconds, 15, 5, and 1 second. ISO 3200. [ed: Plate-solved with nova.astrometry.net which reminded me where I had gone.]

The D star of H 5 7 is obvious, above, at the 11 o'clock position (north-west).

Below, the same distance, is an equally bright star. SkyTools says this is E. The software uses a deep, dark blue to render it but I think it's blue-white like A and D.

There's a faint unequal double beyond mu D: that's BD -21 04905 aka GLP 13, oriented roughly east-to-west. Wide. Blue-white and grey.

On the left side of the image, there is a very faint tight pair: ARA 1142. White and orange, with the orange star to the east. Nearly equal intensities. Almost the same angle as GLP 13.

Now when I saw ST3P saying that μ was a five-star system, I started dropping the exposures, to prevent the primary from drowning out the others.

In the 5 second shot, the dimmer B star clearly emerged from the glare. Not exactly inline with D, a bit to the right. About the 12:30 position, which would be west of A. It's actually visible in the long exposure, as a bump!

The C element is the most challenging. Inline with E but the dimmest, at magnitude 13.0 (per the chart). I believe I see it when I zoom into the high resolution image, below A, on the way to E, at the edge of the glare, very faint. Similar to other mag 13 stars in the image.

I am confident I can see all five elements!

OK. Done with photography.

Retrieved the body cap, unmounted the camera, and set it on the ground.

1:47. Shot darks for the open cluster data at 25 seconds, ISO 3200.

Grabbed the house keys...

1:57. Verified 10 darks were made.

2:00. Disconnected computer and camera.

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