238 replies to this topic

[Adam Long]

Although the Uk has been under high pressure for the last couple of weeks, the clear skies have been accompanied by a cold northerly airflow and large diurnal temperature range. From my urban backyard this has mostly meant disappointingly poor seeing.

 

After a long look at the moon last night, where despite 14" of aperture I only had a fleeting glimpse of the central crater in Plato, I had a look at Algieba and realised I might just be able to get on to Omega Leonis (the view to the south is very restricted). It was easy enough hopping across with the finderscope, but with the coma corrector and medium power I could only see a fuzzy elongation and, defocused, it was apparent the star was already sliding behind the neighbour's chimney. Switching the CC out for a 2x barlow was a big improvement - a steady, wide split that had me double checking the separation - not the view of a sub-arcseconder I'm accustomed to from smaller scopes!

 

I made a quick estimate of PA at 150^o; 30 degrees out but it was behind the chimney before I'd properly established the direction of drift. One I'll be returning to.

[R Botero]

Adam

 

Very true on the temperatures.  It's very warm today but it's supposed to stay clear and with good seeing tonight. I have dressed up my Mak in insulation which helps with thermal currents but I still leave the roof of my RoR open at least an hour before I start observing.  Maybe two hours today as it's so warm.

 

Roberto

[rugby]

BU 1082 UMA: 5.0-7.8; 0.556; 160 (2021)
Despite a stable night, I was unable to elongate this close pair in a 6-inch refractor with powers up to 400

[John Fitzgerald]

STF 1037 Gem. m 7.2,7.3 sep 0.9" at PA 304.  With my 6" apo at 203x, on 4/19/2021, I was able to discern a peanut shape, and discern the approximate PA, despite quite less than optimal seeing conditions.  I expect I could have obtained a clean split if the seeing conditions had allowed me to ramp up the power to near 250x.

[fred1871]

STF 1037 AB is a binary, Grade 2 Orbit, 118 year Period. In recent years decreasing separation. Only observation I have of it post-2010 is from 2012, when separation was 0.98" (from speckle measures) and with my 140mm refractor at 230x it was a barely split double, equal brightness, clear two discs in a bit of scattered light. Dawes for 140mm is 0.83". Rayleigh about the same as the (then) separation. Back then definitely easier than nowadays....

 

Based on the Ephemeris the separation would at present be ~0.80". Dawes for a 6-inch is 0.76", so it should give a very close split appearance in good seeing. A peanut under not so good conditions sounds like a good result.

Edited by fred1871, 24 April 2021 - 12:50 AM.

[fred1871]

BU 1082 UMA: 5.0-7.8; 0.556; 160 (2021)
Despite a stable night, I was unable to elongate this close pair in a 6-inch refractor with powers up to 400

That separation is about 0.6-Rayleigh. And your listed magnitudes give a difference of 2.8 magnitudes. I think I'd be more surprised if I did get an elongation 

 

It'll be very seeing dependent. Especially with a marginal aperture, as the numbers suggest for a 6-inch. With near equal brightness, seeing elongation would be reasonably expected on a good night; but that's a steep delta-m to deal with and significantly changes the possibilities.
 

[rugby]

Thankyou to John F for bringing my attention to STF 1037 in Gemini. Fred is as right as rain describing what should be visible in a 6-inch refractor. Using powers from 200 to 486 I found two discs touching if not slightly separated. A perfect pair to study the Dawes limit of this aperture.

[rugby]

Yet another close pair: STF1555

A beautiful system sitting North of Leo's haunches. The Stella Doppie data: 6.4-6.7;0".649 (2021);150.8.
At this magnitude I get a deep notch between the Airy discs but no black line. The southern component is obviously fainter but appears fuzzier in appearance. All this seen in a 6-inch refractor using a 2.5 Nagler at 486x.
If you star hop get ready for a difficult find; there are few bright stars in the vicinity.

Edited by rugby, 05 May 2021 - 01:33 PM.

[Voyager 3]

Thanks @rugby , I will give that a go , if seeing and clouds permit. 

[Pete W]

Checked out omega Leonis (5.7 & 7.3 @ 0.9") last night with the 6" Orion Argonaut Mak-Newt.   Seeing was pretty good for central TX.  An obvious peanut at about 120X.  With the 2-4mm nagler zoom at 300x the gap was occasionally visible, but mostly looked like a snowman with a very narrow waist.

 

 

While in the neighborhood I slid westward to zeta Cnc.  All three members were quite visible at X120 and more obvious at 220x.   At 1.1" the tight pair violates the <1" of this thread, but it's pretty close.

[Adam Long]

One from a couple of weeks back:

 

STF 3121 in Cancer. A very close, evenly matched pair, mags +7.9/ +8.0, which appeared to me to a warm yellow/orange colour.

 

Stelledoppie has the headline 'separation now' at 0.48", but the star appeared closer to me. I was unable to get a split with my 14", instead recording an overlapping pair/ notched rod at 520x. A comparison check with my go-to super-tight pair Phi UMa / STT 208 (0.42") showed a clear split, although it is both bright and much nearer zenith so that may have helped.

 

A closer look at the Grade 1 orbit of STF 3121 shows it closing fast, at 0.43" at the start of 2021 and down to 0.37" by the start of 2022. My observation would suggest a little closer than that but the Grade 1 orbit and the star's position in it  - i.e. not at perisatron where the smallest error in timing would be magnified - seem to leave little wiggle room.

 

Be interested in any other observations, especially as for me the rapidly lengthening evening have already put this star behind the neighbour's chimney until next year.!

[rugby]

STF 1728 Alpha Comae Berenices

On the evening of May 9 2021 I set out to repeat AstroJensen's results with this tight pair. I observed with an ES 152 triplet. The air was very stable. I had tried several times in the recent past but always failed for one reason or another. However this time I saw an elongation almost immediately when using around 250x. I increased the power to 606x with a 2mm Vixen HD and the rod-like elongation remained. I guessed 210 degrees for P.A.. For certain the position angle was greater than 180. Following is an excerpt from William H. Smyth.s The Bedford Catalogue regarding this pair:
"When I first attacked this object in 1832, it appeared quite round; and I several times returned to it with similar results. At the middle epoch above recorded (1839-40) however though I could not raise a vacancy between the individuals or even palpably notch them the elongatio was so distinct under a power magnifying 850 times as to be capable of a tolerable estimation..."

Edited by rugby, 11 May 2021 - 08:55 PM.

[Tyson M]

Great thread. I'm gonna make a list of these targets to try and tackle with my 9" istar and chromacorr.

[fred1871]

One from a couple of weeks back:

 

STF 3121 in Cancer. A very close, evenly matched pair, mags +7.9/ +8.0, which appeared to me to a warm yellow/orange colour.

 

Stelledoppie has the headline 'separation now' at 0.48", but the star appeared closer to me. I was unable to get a split with my 14", instead recording an overlapping pair/ notched rod at 520x. A comparison check with my go-to super-tight pair Phi UMa / STT 208 (0.42") showed a clear split, although it is both bright and much nearer zenith so that may have helped.

 

A closer look at the Grade 1 orbit of STF 3121 shows it closing fast, at 0.43" at the start of 2021 and down to 0.37" by the start of 2022. My observation would suggest a little closer than that but the Grade 1 orbit and the star's position in it  - i.e. not at perisatron where the smallest error in timing would be magnified - seem to leave little wiggle room.

 

Be interested in any other observations, especially as for me the rapidly lengthening evening have already put this star behind the neighbour's chimney until next year.!

Based on the Ephemeris, 1/3 into 2021, it would be 0.41" at the time of your observation. Looking at the speckle measures, 34 years ago is 1987, when McAlister got a measure at 0.40", speckle measure on a large 'scope (3.8-metre).

That's a near-enough match So the 0.48" is definitely too wide, and around 0.41"/040" should be accurate.

 

This is a binary of 34 year Period, so it moves quickly in much of the orbit. Slower in the widest part, where Horch (3.5m with speckle) measured 0.78" in 2004 (much the same for 2035), when it will be much easier.
 

[Jeff B]

Checked out omega Leonis (5.7 & 7.3 @ 0.9") last night with the 6" Orion Argonaut Mak-Newt.   Seeing was pretty good for central TX.  An obvious peanut at about 120X.  With the 2-4mm nagler zoom at 300x the gap was occasionally visible, but mostly looked like a snowman with a very narrow waist.

 

20210506_115011.jpg

 

While in the neighborhood I slid westward to zeta Cnc.  All three members were quite visible at X120 and more obvious at 220x.   At 1.1" the tight pair violates the <1" of this thread, but it's pretty close.

Doing double tonight and looked up Omega Leonis.  Pretty steady skies and I could easily see the split wink in and out at 180X and was steady at 240X with my TEC 200ED, Denk BinoTrons at 2.8X and a pair of Denk 21 LOA neutrals.

 

Very pretty!  

 

Jeff

[Jeff B]

So, in the AP hand paddle ADS list of doubles there is number 09425 listed as "Omicron Sigma 288 Boo" at .8".  Visually, at 240x with my TEC 200ED and binos, it's striking and I see them as two globes touching, one blueish-white and the other reddish-orange.

 

I can't find it on the net though.

 

Jeff

[John Fitzgerald]

That's STT 288 in Bootes.  WDS gives a current separation of 0.93" at PA 155 deg., magnitudes 6.9,7.6.

[Jeff B]

That's STT 288 in Bootes.  WDS gives a current separation of 0.93" at PA 155 deg., magnitudes 6.9,7.6.

 

[Adam Long]

Based on the Ephemeris, 1/3 into 2021, it would be 0.41" at the time of your observation. Looking at the speckle measures, 34 years ago is 1987, when McAlister got a measure at 0.40", speckle measure on a large 'scope (3.8-metre).

That's a near-enough match So the 0.48" is definitely too wide, and around 0.41"/040" should be accurate.

 

This is a binary of 34 year Period, so it moves quickly in much of the orbit. Slower in the widest part, where Horch (3.5m with speckle) measured 0.78" in 2004 (much the same for 2035), when it will be much easier.
 

Thanks Fred, that's really useful. I'd come to a similar conclusion on current sep which is why I'd been expecting a split.

 

For most stars I can't see info on measure via Stelledoppie, do you get them direct from the WDS?

 

Is there strict criteria on how the orbits are graded or is there some subjectivity? I presume there is always some room for fine-tuning.

 

A good star to keep an eye on anyway - tight but 90^o PA change over the next decade by which time it will be widening rapidly to an easier prospect.

[mccarthymark]

Adam, you can find in StelleDoppie next to the orbital representation a list of the past and expected separations / PA (which AFAIK StelleDoppie pulls from the 6th orbital catalog, specifically the ephemerides).  If it was 0.433" on 1/1/21, and to be 0.370" 1/1/22, then 0.433-0.370=0.063" change between 2021 and 2022, and if we're 1/3 in to 2021, so 0.063/3=0.021, subtracted from 0.433, = 0.412" currently.

 

See here for how orbits are graded

 

 

 

I split this a couple nights ago in my 20" @ 533x: "Light yellow-orange stars, 1 delta mag, clean well split." -- I plan to follow this annually through its orbit.

Edited by mccarthymark, 13 May 2021 - 10:46 AM.

[Adam Long]

Yes, I've been using the ephemerides, I suppose what I was after was what the error margins are on each prediction. Always wary of that sort of three significant-figure precision like that!

 

That orbit grading link is just what I was after, thanks, have added to my bookmarks.

 

Will struggle to observe this one again this year now but will be sure to visit it next year, hopefully might be able to get a split before it closes too much.

[Spikey131]

That's STT 288 in Bootes.  WDS gives a current separation of 0.93" at PA 155 deg., magnitudes 6.9,7.6.

I found this one tonight.  The seeing was good, and it was nicely split with a C8 and Nagler Zoom at 333x.

[Pete W]

Tonight I tracked down three  sub-arc sec pairs in Cygnus with my vintage orange C5 in the backyard using Toshimi Taki's Atlas of Double Stars.  Seeing was pretty good for Central TX.

 

 

STT410:  mag. 6.1, 6.8; Sep. 0.9", PA 3 deg -   Elongated with the 7.5mm Ultima (167x) and with the 5mm Tak LE (250x) during fleeting moments I believed I could see the gap, if not a very thin-waist snowman.  The pair seemed more equal than the listed mags.

 

STT 403 (part of STF 2657): mags. 6.8, 7.6; Sep. 0.9", PA 171 deg -  STT 403 is part of a triple.  Very similar to STT 410 with almost the same orientation - north-south.  A bit tougher, though I believe the sep is actually a bit wider than 0.9".  About 11" away is the 9th mag star making up the STF 2657 pair; STT 403 is the brighter member of the STF 2657 pair.

 

STF 2741: mags. 5.6, 6.8; sep. 2.0"; PA 25 deg - OK, this one's not <1" but it was on the way to the next pair listed below.  Nice and wide at 250x compared to the others I was tracking down.  reminded me of the fainter pair in the double-double.

 

BU 155: mags. 6.9, 8.1; Sep. 0.7"; PA 42 deg - at 250x in the 5mm it was readily elongated with the "bump" on the trailing edge of the drifting star.  The orientation of the "bump" was noted before looking up the PA to confirm.  Not "split" but its duality was definite.  

Edited by Pete W, 26 July 2021 - 10:25 AM.

[daedalus]

I had a night of good seeing in New England, so after measuring 3 doubles in Cygnus, I decided to try a split at the Rayleigh limit of my scope.

HU758, theta 144, rho 0.92 as listed in WDS.
Sky Watcher 150ED, F=1200mm Rayleigh limit of 0.923
Seeing Pickering 8 (measured from Deneb at 600x, dew heaters on), transparency as NELM 4.8
Elongated at scope's diffraction limit magnification of 150x, but there were occasional hints of separation
Hairline separation at 200x, split comfortably at 235x, estimated theta SE, say 135 or so.
Best view at 400x

At greater magnifications, the system was dimmed so much that I needed averted vision to see it, and it was too dim to see the split comfortably. This binary was way too dim to try to measure with a Meade astrometric eyepiece and barlow combination.

I'm celebrating as I write this post with bourbon and a cigar, sitting out in the early morning wathcing Orion rise over the Eastern rooftops. A very good night.

[fred1871]

Interesting description of the observation, made more interesting by finding the magnitudes in WDS are 9.42 and 9.43, so this qualifies as a dim pair rather than a 5th-6th mag bright pair, when dealing with only 6-inch aperture.

 

A pleasing result, but part of the story at this magnitude level/aperture is having enough magnification for the human eye to deal with the modest amount of light. Lewis's classic 1914 paper on what could be seen with various apertures, for brighter and dimmer pairs with a variety of apertures, came up with clearly lesser resolution with the dimmer pairs compared to brighter ones. This was with many of the famous observers of his time and before.

 

Personally, I'd want good seeing and a dark sky to attempt a pair as faint as this with only a 6-inch. Very tight for the aperture. A good result. If it were say 3 magnitudes brighter I'd expect it to be much easier, likely split comfortably at 150x with good optics and good eyesight etc.