18 replies to this topic

[Nucleophile]

Of late I have been observing primarily with my 8” f/5.9 reflector.  After collimation, I check the seeing via visual observation at moderately high power on tight and/or magnitude contrast doubles—this is how I happened on this pair of doubles in Draco.

 

STT 312AB and STF 2054AB appear to the naked eye as the single star Eta Draconis.  Starting in Ursa Minor, a straight-line path from Kochab through Pherkad gets me to Eta as shown in the annotated Cartes du Ciel screenshot below.

 

 

I like to start with the fainter pair, STF 2054AB which is  a mere 12’ due North of Eta Draconis.  In 2017 this mag 6.2/7.1 pair had a separation of 0.943”, which is in line with historical speckle data.  At 345x, I saw two whitish stars of slightly uneven magnitude that were clearly split with dark space between the stars.  I gauged the seeing by estimating how often the image sharpens to two distinct discs.

 

The 2nd Ed. of CDSA lists STF 2054 as a (2) + 1 triple, meaning the A component is really AaAb.  Stelle Doppie informs the AaAb pair is CHR 138AaAb with a separation of 0.222” (1990)—perhaps those with larger glass can see this as oblong?

 

Moving on to the brighter object, Eta Draconis or STT 312 AB is where the fun starts.  This mag 2.8/8.2 pair has a separation of 4.68” as measured by Gaia satellite (2015.5)  Using the same eyepiece you used for STF 2054AB, try to find the faint secondary without prior position angle knowledge.  It will be quite small and about 4.5x farther than the distance between the stars comprising STF 2054AB. 

 

My first attempt at detecting STT 312 B required almost a half hour of moving my eye from averted to direct vision before I definitively saw the tiny speck of light corresponding to the companion.  On a subsequent night, I found the secondary right away because I knew where (and how) to find it.  The more steadily the diminutive B presents as a dot of light, the better my seeing.  Of course, darker skies will also aid your efforts for seeing the faint companion. 

 

STF 2054AB and STT 312AB help me gauge my local seeing and are fun to look at.  Have you looked at these stars lately?

Edited by Nucleophile, 25 May 2019 - 06:30 PM.

[Nucleophile]

Perhaps the aforementioned objects are too easy and you desire a greater challenge; if so, head about 11 degrees due south of Eta Draconis to Hu 149

 

This pair of ~matched magnitude 7.5 stars has a separation of 0.66" (last precise in 2017 = 0.665"; my own measure in 2017 = 0.662")  The pair are slowly widening:  Burnham (1978) lists the separation at 0.5"

 

Using my 8" reflector, I observed this object last night and logged the following observations:

 

345x:  image transforms from elongated to notched (snowman) about 30% of the time; both stars are light orange-yellow

460x:  now seen as sitting on the border of resolved to two discs and split with the tiniest of black space between the discs

 

Below is an inverted image of Hu 149 I assembled in 2017 using my 15" reflector and an ASI178MC camera at f/23 operating in mono mode.

 

[John Fitzgerald]

I saw Eta Draconis as double last night with my 6" Apo at 203x.  It's a notoriously difficult object unless the seeing is steady.   The secondary would pop in and out as the seeing varied.  

 

Also observed Mu Dra, STF 1984 (yellow and blue to me), STF 2179 (nice, unequal pair), STF 2180, STF 2199, all these at 174x.  The seeing was highly variable,  but mostly mediocre. 

[C.Hay]

Dear Mark,

 

Thanks a lot for your interesting and well-documented presentation of a pair of doubles so well suited to gauging seeing  all year round. Last night I made these my first port of call with a 140mm Maksutov (an OMC 140 made by Orion UK, a good instrument). The physics suggest that the separation of 0.943” which you state for STF 2054AB is at the physical limit possible with this aperture, so I was keen to find out how I would fare.

 

The day had been hot, seeing was mediocre. I know from experience, though, that the air may calm down in certain phases of the evening, so I just hoped I would catch a good moment. At 75x I saw no hint of a companion of Eta Draconis, but STF 2054AB was definitely elongated. At 130x still no sign of Eta's companion, but the elongation of STF 2054 became even more evident and it was clear at which end the weaker component stood. Encouraged by this, I went up to 210x. Now STF 2054 was a stretched figure-8 that popped apart into separate discs in better moments of seeing. Somehow quite charming!

 

I had gone in without PA knowledge and estimated this at 330°. Stelledoppie says 351°. So deviation <10%, that's OK.

 

After having trained the eye in this manner, I turned my attention to Eta Draconis at 210x. All I could spot was a disc within a wildly dancing diffraction pattern. Although the B component, with its separation of 4.68”, is more than 4.5x further than the distance between STF 2054 A and B, it is evidently much harder to spot. This was an interesting lesson in the effect of Delta-Mag.

 

I find STF 2054 quite charming and Eta quite challenging, and will certainly be returning to them often. So thanks again, Mark.

 

CS, Christopher

[Nucleophile]

Excellent report, Christopher.

 

I will try to image these objects in the coming weeks and will post my results at that time.

 

-Mark M

 

PS if you have a favorite dark site, try Eta DRA there and see what happens!

[John Fitzgerald]

η Draconis is a difficult object unless the seeing is good.

[Nucleophile]

Attached are some recent pictures of these double stars.  In all cases, N is up and E is left.

 

I obtained the images using my 15" reflector and an ASI 290MM cooled CMOS camera.  An imaging train of Paracorr type 1 (setting 5), Powermate 2.5x and a Baader Orange filter gives an f ratio of 13.3  Images were collected using either SharpCap or Firecapture. 

 

Measures were made with Speckle ToolBox.  Composite images were assembled in Registax.

 

First up is STF 2054AB

 

   

Edited by Nucleophile, 17 June 2019 - 09:38 AM.

[Nucleophile]

Next is STT 312AB

 

Look closely at the 7 o'clock position to see the very faint secondary

 

   

Edited by Nucleophile, 17 June 2019 - 09:49 AM.

[Nucleophile]

Finally, here is Hu 149

 

I measured this one 21 times over three nights in order to gauge repeatability of the measuring protocol.  The current measure matches very well what I obtained a few years back.

 

   

Edited by Nucleophile, 17 June 2019 - 09:43 AM.

[rugby]

I just finished observing STF 2054 AB and STT 312 in Draco using an  SW 120 ED and a Meade LX 10. A very bright moon with Jupiter brightened the eastern horizon.  Unfortunately these pairs lie directly above my house and thus suffer from heat rising from the roof. 

What I saw was surprising. 2054 was elongated but not separated in the 120 at 200x.  I had not expected anything because it is on the edge of this scope's capabilities. I did not try the 8 inch.

STT 312 AB was exceedingly difficult. Without prior knowledge of PA I kept seeing flashes of a tint dot south south preceeding the primary. I used the 120 at 200x. The view in the 8 inch was too turbulent for any resolution.

I am notoriousy poor in estimating position angle.

[Nucleophile]

I just finished observing STF 2054 AB and STT 312 in Draco using an  SW 120 ED and a Meade LX 10. A very bright moon with Jupiter brightened the eastern horizon.  Unfortunately these pairs lie directly above my house and thus suffer from heat rising from the roof. 

What I saw was surprising. 2054 was elongated but not separated in the 120 at 200x.  I had not expected anything because it is on the edge of this scope's capabilities. I did not try the 8 inch.

STT 312 AB was exceedingly difficult. Without prior knowledge of PA I kept seeing flashes of a tint dot south south preceeding the primary. I used the 120 at 200x. The view in the 8 inch was too turbulent for any resolution.

I am notoriousy poor in estimating position angle.

Hi Rugby,

 

give 'em a try with your 8"--I think you will like the views!

[rugby]

At long last....success!   My fourth attempt at Stt 312 AB showed the tiny secondary using an 8 inch f10. I used a Morpheus 12.6 yielding 158X. It was a direct vision object clearly separated from the primary

[ssmith]

Here is a photo of STT312 taken with my C9.25 @ prime focus (f10) single frame jpg - ISO 500 , 1/3 sec.

 

[Nucleophile]

Steve, a question on your imaging protocol:

 

When faced with challenging targets such as this one, where do you start with respect to integration time and sensitivity?  Do you keep a log of successful conditions used for similar past targets?  Just curious.

[ssmith]

Hi Mark -

It is somewhat of a trial and error procedure. At the stated separation of ~5 arc-sec I knew from past experience that the image scale at prime focus should be sufficient provided that the air was steady enough to allow an exposure long enough to capture the much fainter secondary. I find that larger image scales can be counter-productive when trying to capture very faint secondaries since the required exposure times increase dramatically which may not be supported by the seeing.

I usually start at about 1 second exposure @ ISO 800 and then look for elongation or any hints of the secondary. If nothing is seen I will progressively shorten the exposure times hoping to better freeze the seeing and capture the secondary. I then play with the ISO to optimize the image.

I use a mirror-less DSLR for my imaging so I am usually viewing the object through the electronic viewfinder of the camera which can magnify the image on the sensor by 3x, 5x, 10x or 14x. I rarely look through an eyepiece unless I have my flip mirror diagonal installed in the imaging train. For Eta Draconis the secondary was clearly visible through the viewfinder at 14x using prime focus so I knew my chances of capturing the image were good.

[R Botero]

Here is a photo of STT312 taken with my C9.25 @ prime focus (f10) single frame jpg - ISO 500 , 1/3 sec.

Eta Dra STT312 C9 6-23-19 111 edit close 1x1.jpg

Excellent shot! This is a high contrast one. My observation notes (of STT312) in 2017 and 2019:

June 2017
“Striking magnitude difference. PA140-150. Yellow and white blue. Secondary barely visible in glare of primary. ”

May 2019
“Extreme contrast!”

Roberto

[fred1871]

Excellent shot! This is a high contrast one. My observation notes (of STT312) in 2017 and 2019:

June 2017
“Striking magnitude difference. PA140-150. Yellow and white blue. Secondary barely visible in glare of primary. ”

May 2019
“Extreme contrast!”

Roberto

Even more interesting if you told us which telescope/s you were using at the time.   

[fred1871]

Interesting. Both Eta Dra (STT 312) and STF 2054 are listed in Sissy Haas's Double Stars for Small Telescopes book, and in both cases she describes the pair as seen with her 5-inch (achro) refractor at 350x. STF 2054 was seen by her as a figure-8; Eta as a "brilliant... star almost touched by an elusive wisp of light".

 

I happened upon both of these doubles back in the mid-1990s when I had six months observing from North County San Diego, Ca, and took notes on some 500 or so doubles that are too far north for me to see from my normal residence in the Southern hemisphere.

 

Using a C8 of average quality (one of several I got to use at the time), the little companion of Eta Dra was just visible at 200x, and no better at 330x. STF 2054 was elongated at 135x, split at 200x, not difficult with the latter power. Well separated at 330x. HU 149 was apparently not on my object listings at the time, so no notes on that one. As always, seeing conditions matter, and I recorded the seeing on that night as 'good' rather than middling or excellent.

 

Regarding the note by 'rugby' above (#10), the separation of STF 2054 should be expected to be seen as elongated with 120mm, as the brightness difference is just under 1 magnitude, and an uneven brightness elongation, at about 0.8-Rayleigh for the aperture, should be visible. 

Edited by fred1871, 02 July 2019 - 06:31 AM.

[R Botero]

Even more interesting if you told us which telescope/s you were using at the time.

Indeed. The vast majority of my double star observations have been made with a 10” f/20 Maksutov from TEC. The ones above at 250x.

Roberto