Special Observing ReportBackyard Boulder Creek: April 22 - May 1, 2002
Doubles in Ursa Majoris Doubles In Leo and Ursa Major Revisited Disparate Doubles Blues A Definitive Night Out Wrapping Things Up?
Doubles in Ursa Majoris
With a 65% Moon floodlighting the sky, went on a double star splitting spree. Started around 8:30PDST and wrapped things up at 11pm (but left 150mm MCT Argo parked outside to catch Selene later as she clears the foliage.) By quitting time, could just hold the three stars comprising the Herdsman's club (east of the Big Dipper's handle). So even with Luna keeping as much of the sky to herself as possible, could just manage stars unaided (and direct) down to magnitude 4.5.
Telescopically, things were better. At 210x (the only magnification used all evening), was able to just hold a 12.7 magnitude test star in Praesepe. Referencing
Having backgrounded on the seeing, and equipment, let's move on to get an idea of what I did and did not see this evening...
Polaris: Well before skydark, just able to hold the Pole Star's faint 18 arcsec separated companion at 220x. This just after beginning the evening's activities. At that time, it was pretty tough seeing the dimmest star in the Big Dipper - magnitude 3.4 Delta UMA (Megrez). I know, I know Polaris is EZ - but check it out sometime at high magnification through a bright sky and before dark adapted. It's much easier at low power when its really dark out.
While in the Little Bear attempted KU 1. Here's the data for this pair out of the Saguarro Astronomy Clubs Double Star Database:
Name Star RA Dec Comp Mag1 Mag2 Sep PA U2000 Spec Notes
KU 1-AB 16 43.0 77 30 AB 6.1 9.4 2.7 184 11 F2 ALSO HU 917
With a magnitudinal delta of 3.3 and separation 2.7 arcsecs, this baby definitely qualifies as a tightish disparate. Given an early hour and relatively disadvantaged sky position, it's not surprising I was unable to locate the secondary - though I thought I saw something trailing and to the north... (But Wrong PA!)
So from Ursa Minor moved to the Major. Started with:
HJ 2477-AB IOTA UMA 08 59.3 48 02 AB 3.9 9.5 4.5 24 70 A5 AXBC: Orbit calc\'d. A is a Delta Scuti var and sp-bin.
This super-deltified (5.6 magnitude), closish (4.5 arcsec) disparate has plagued me for over a year now. Of course, I only seem to go after it when there's a moon - but that really is no excuse... In Iota's case, I consistently seem to pick up something on the visual threshold, leading and to the south. Again wrong PA!
This same issue applies to the even dimmer companion of Upsilon UMA. At best I seem to pick out a threshold secondary leading and to the south. And tonight was no exception. (BTW: No scope I've ever looked through has shown 3.9 magnitude Upsilon's, 11 arcsec separated 11.5 magnitude companion. Give it a shot! And email me if you succeed.)
So just to get some kind of feeling of success, dropped by 23 UMA for a look at a nice wide yellow-blue pair with secondary leading due west. This double has a nice color contrast and warrants a view whenever heading further north to take in the M81/82 Great Galactic Duet.
Next on the list:
STF 1306-AB SIGMA UMA 2 09 10.4 67 07 AB 5.0 8.2 3.0 3 23 F8 \"P = 1067 yr., a = 6.20\'\', motion retrograde.\"
That taste of success payed off! Had no trouble distinguishing this yellow and blue-grey pair. Secondary pretty much due north, close but with a clear gap. The fifth magnitude primary showed a well-defined airy disk with walking first diffraction ring and only a little flare. This in contrast with the virtual images of the brighter fourth magnitude primaries of the evening whose airy disks, though perceptible, were engulfed in randomly scattered luminosity ejecting visibly outside what didn't really pass muster as a first diffraction ring...
Thence to:
STT 199-AB 09 20.7 51 15 AB 6.1 10.2 5.7 133 44 F2
Thought I caught a faint secondary maybe 5 arcsecs south of and slightly leading the primary across the sky (PA~200 degrees). Although separation was pretty accurate, (I don't take double star data with me to the eyepiece) position angle off significantly. So a no go - unless the database is awry or out of date...
Continuing:
HO 377-AB 51 UMA 11 04.6 38 14 AB 6.1 12.6 8.2 250 73/ 106 A2
Here I made out a pearlescent (bluish white color - rare in UMA) primary led to the south by a detection threshold level faint secondary at about 8 arcsecs. Both PA and separation are quite accurate BUT, 12.6 magnitude is very dim! This one definitely needs a darker sky. (Despite the fact that Argo held stars down to 12.7, there is always some sky glow close to 6th magnitude stars.)
STF 1523 XI UMA 11 18.2 31 32 4.3 4.8 3.0 129 106 G0 Also 53 UMA
Although the current separation is now closer to 2.0 arc secs, Xi remains an easy split for Argo at this magnification - even through 6/10 skies. Both stars are yellow suns, and of approximately the same brightness (a matched pair). Visibly fainter secondary leads to the south (PA ~ 235 degrees - an obvious example of out of date data.)
Next study:
STF 1524 NU UMA 11 18.5 33 05 3.7 10.1 7.3 147 106 K0
Nu proved to be a remarkably definite resolve! The faint grey secondary could be seen some 8 arcsecs trailing and south of a brightly flashing yellow primary.
Then: STF 1543-AB 57 UMA 11 29.1 39 20 AB 5.4 8.4 5.5 358 73/ 106 A2 A is a sp-bin.
A second pearlescent primary. This time led slightly to the north by a purplish secondary some 5 arcsecs distant. This is a fun one for a three inch and shows a satisfying color contrast through six inch instruments. High power not necessary, but I stayed lazy throughout the night. (The old 3x configured barlow and longish eye relief 15mm Ultrascopic eyepiece inertia trick.)
Of course, to balance out that recent string of successes moved on to:
BU 919 11 59.3 33 09 6.0 12.0 4.5 16 107 K0
Thought I caught a faint companion some 5 arcsecs trailing and to the north (~PA 70). Either another mis-perception or out of date PA. Needs to be revisited on a moonless night...
And now the real treat of the evening:
STF 1695-AB 12 56.3 54 05 AB 6.0 7.9 3.7 280 48 A2 A sp-bin.
Easy locate just south of Epsilon UMA. Lovely colors! Warm yellow primary with blue-green secondary. Both stars show a diffraction disk (though the secondary's is almost pointilistic and there is no diffraction ring - sign of threshold airy). Secondary leads the primary to the west. If you are going to view only one double from this list, this is the one!
Well everybody seems to complain about the Moon. Doubles are one way of doing something about it!
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Doubles In Leo and Ursa Major Revisited
Staked out some eighteen doubles (excluding those usually dropped in on) for observation during the lunar second quarter. As it turned out, the May Full Moon came and went before conditions improved enough to complete this venture. Even so, conditions were really no better than they'd been five days earlier. By the time things wrapped up this evening (11:00PDST) - the Moon once again emerged. Meanwhile, rapidly falling temperatures and a late start getting 150mm MCT Argo out meant continuous (but relatively mild) tube currents throughout the evening. The sky was none too supportive either. Rapid changes in air temperature plus thermal currents from a warmish earth meant 6/10 stability. Add to this variable cirrus clouds above and you can understand why I may not have been 100% successful making pairs out of single stars...
Of course, before launching into the evening's program, dropped in on Jupiter at 210x. Actually, and (quite momentary) got a fine 7/10 seeing view: Rifted SEB. NEB Belt-edge irregularities. White oval approaching the CM. Diffuse EB. Well-delineated NTB, and a definite STB. But the Galileans showed walking disks and soon began to flare as the scope sensed a distinct change in temperature with the change in venues. Well, when you get a Mak you also get a lesson in this sort of thing!
Turned Argo on the pearly-white Castor pair. Very distinct - but no sign of airy disks or diffraction rings. Simply much too luminous for sky conditions. Theta Auriga? Obvious but disparate secondary due south that lay safely beyond the flashing tentacles of its brightish primary. Theta, like Castor, will soon be lost to us. Gamma Leonis? Like Castor, widish and easily resolved. Due to dimmer apparent magnitudes however, a better sense of distinction between airy disks and diffraction rings. Like Castor, quite lovely with perhaps a more intriguing set of colors (warm yellow primary, and blue-tinged secondary). The obviously dimmer companion trailed to the south.
Now on to a few studies I'd been attempting from various locales all week with little hope of success. First off:
Name Star RA Dec Comp Mag1 Mag2 Sep PA U2000 Spec Notes
STT 523 39 LEO 10 17.3 23 06 5.8 11.4 7.6 299 144 F5 Mt. Wilson spectral types are F1s and dM1.
Despite the relative dimness of the primary (magnitude 5.8), only caught glimpses of extinction level (probably imaginary) secondarys at a variety of position angles. Meanwhile, tube currents created an apparent brightening on the first diffraction ring. This could easily have led me to believe I'd seen a disparate playing "ring around the rosy"! So, nothing here. I'll just have to keep coming back until I get that one super-fine night of superb transparency AND stability. Like Iota and Upsilon UMA, this one could prove to be a life-long commitment!
Hw about Kappa Leonis?
BU 105-AB KAPPA LEO 09 24.6 26 11 AB 4.6 10.4 2.4 211 143 K0 Y/B
Surely at magnitude 10.4? Well, again nothing definitive. Possible bluish companion south and slightly trailing. This near the region of what would be a first diffraction ring on a better night. Well, lets see south and slightly trailing is somewhere around PA 143 degrees isn't it? Hmmmm... This one is close. Except that south and trailing is where the brightening on the first diffract tended to be. Could be a case of "wishful thinking". Another night, the same double, methinks. But doable!
Dropped southeast of Rho Leonis for:
STF 1450 49 LEO 10 35.1 08 39 5.8 8.5 2.2 157 190 A0 A is the Algol-type system TX Leo.
Here we find a nicely-joined pearlescent primary with 8th magnitude aqua secondary south and trailing about 2 arcsecs. Looking at the data above, the PA seems a bit awry but this was a definite resolve and not simply a brightening on a diffraction ring. I'll take it!
Now one thing I noticed about Leo that distinguished it from Ursa Majoris was the greater frequency of "pairs of mixed color". Yep, the old Lion has a bit of the peacock about itself while that "earthy bear" never seems to stray too far from your basic population I yellow!
Thence east toward Sigma and:
KUI 54-AB CHI LEO 11 05.1 07 20 AB 4.7 11.0 3.6 268 191 F0
Time to get my "Chi" circulating... Here I find a yellow primary with distinguishable airy disk preceded slightly to the north by an extinction-level "secondary" separated by about 5 arcsecs. Had the PA not progressed to almost south-southwest year 2000, I might almost believe I had resolved this one. Certainly more visits under better conditions should reveal the error of my ways.
NOTE: Here is a case of a mistaken read of the datastream above. The value 147 (taken by me as a "progression", is the page number of the Uranometria Star Atlas where this particular double is discussed! So in fact, the secondary may actually have been resolved on this occasion.
Iota Leonis next. This one has plagued me since fellow observer Otto Piechowski first brought it to my attention. Then, on a decent night while snatching views at the Houge Park Public Star Party, got a superb resolve through an AP155 APO. This view should be replicable through Argo (save for a brighter first diffraction ring) but has not yet proven itself out.
STF 1536 IOTA LEO 11 23.9 10 32 4.1 7.3 1.3 141 191 F5 "P = 192 yr., a = 1.92'', motion retrograde."
Here's a bright yellow primary with flashing virtual image leading a faintish secondary. The secondary lies just outside of where a first diffraction ring should appear. And no, I don't think the listed separation is quite right. Probably closer to 2.0 arcsecs than 1.3. Frankly, there is just too much inaccurate data on the web in regards to binary systems. And of course, I'll be back until I get that consummating view!
Well north of Iota, and within the Lion's haunches lies:
STF 1552-AB 90 LEO 11 34.7 16 47 AB 6.1 7.4 3.4 208 147/ 192 B3 B is a sp-bin. W/B
Of all pairs observed this evening, 90 proved to be the most mysterious. Both stars showed airy disks. (The secondary's on the limit of solvability.) Primary showed a certain "faint fuzziness" suggestive of a diffuse first diffraction ring. Though obviously of differing magnitudes, the pair is not quite "disparate" - more an unequal matched pair. The 7th mag secondary lay about 3 arcsecs south and slightly leading the primary. Most intriging was way the two stars "swapped" colors. At any point, one appeared bluish while its mate - orangish. Never could pin 'em down. Just noticed the contrast. Shall we call this one Leo's "Blinking Binary"?
Though the "Blinking Binary" took the prize for "most mysterious", the more northerly double:
STF 1555-AB 11 36.3 27 46 AB 6.4 6.8 0.6 143 106/ 107/ 147 A3 A is a sp-bin
proved the most beautiful. This superb pair displays outstanding color contrast (warm yellow and aqua). It also appeared less evenly matched than suggested above. (Probably a consequence of visual bias toward yellow over blue.) Finally the separation proved to be much wider than the .6 arcsecs annotated above. (Easily distinguishable at 210x - although not very distant. Possibly 1.5 arcsecs or so.) Given these discepancies, might normally begin to think I'd found an entirely different pair. However, the secondary was seen to trail to the south - giving a PA of 135 degrees or so. And this maps quite nicely against the 147 degrees documented above. I am content and will probably revisit soon to get a better sense of what magnification "thinline resolves" the pair.
To be accurate, there was a bit of a delay between observing Chi and Iota Leonis. For you see, Backyard Boulder Creek is a bit disadvantaged foliage-wise to south and southeast. So, while awaiting Iota's emergence, revisited a few doubles in Ursa Majoris. And without comparing views to those documented at
Upsilon UMA: Extinction-level secondary leading and to the south. Absolutely no sign of an airy disk on the bright third magnitude primary.
STT 199: Faint companion 5 arcsecs trailing and slightly south of primary. Best view 150x. This may constitute a hit BUT, there are far too many occasions where I've seen something "trailing and slightly south" in this series. So no go!
Iota UMA: Something I know not what, leading and to south at the limits of a flaring primary spurious stellar image at 210x. No confidence, probably an atmospheric artifact.
Nu UMA: Definite but difficult faint bluish secondary trailing and to south of bright yellow primary.
Xi UMA: Occasional thinline separation at 150x. Confirms 6/10 seeing stability. Resolves cleanly and disticntly under 7/10 seeing at even lower magnifications (120x).
While attempting STT199 didn't have to slew far to locate galaxy NGC2841. Even with the Moon well above the southeastern horizon (and recently post-moonapausal) could detect a starlike nucleus with definite north-south orientation (at 150x). For me all this is a welcome sign change for soon I hope to "reconfigure" for deepsky mode. BTW: In locating this galaxy, thought I caught a very faint companion some 10 arc minutes west and slightly south. Not on my charts...
And, of course, no evening is complete without a telescopic limiting magnitude check. Found I could just hold (with full aversion) the 12.7 magnitude test star in Praesepe at 70x. This through what was probably the average transparency of a sky beset by wafting cirrus clouds. So assuming 6/10 stability. and 11.7 magnitude stars held direct at 70x, dimmest star holdable unaided calculates out to be magnitude 4.8. Yup - I can "just barely" see that...
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Disparate Doubles Blues
Expected no sky this evening at all. Around 6pm, the possibility of an evening "sucker hole" chase emerged. By 7:00, the sky completely cleared and I started "mission planning" in earnest.
First step was to beat the tube currents by setting up 150mm MCT Argo soon as the Sun dropped below the mountains. Then one hour later, sweep the sky for "The Veiled Beauty" using the finderscope.
Then on to The Royal Monarch and Ringed Wonder as the sky darkened further. Once Polaris was visible, move on to follow the emergence of Polaris-B. Then break to double star observing as soon as the companion can be held direct. The goal? To sift through all those unresolved disparates left over from moontide. Upsilon, Iota, and 51 UMA. Kappa, Chi, 39 and 90 Leo - plus a few of them numbered pairs: STF199, HO377, BU919 - all in Ursa Majoris. Everything seemed to be going my way - except stability.
By 8:00pm, picked up Venus by sweeping the sky with the finder. With Argo pointing the way, was quickly able to detect the planet unaided. Venus showed maybe a 70 percent gibbous disk along with a brilliantly illumined leading edge and CM transition to a softer pearlescent glow. With Venus positioned some 30 degrees above the horizon, not quite able to get clean edge focus. As at Monte Bello last week, no atmo-chromaticism detected. Did notice a thin diffraction spike impaling the planet. But soon realized I was peering past Ajax's (canine member of the household) runline. One thing nice about Refractors, Maks and SCT's - no spider vanes. Very nice feature when viewing intensely brilliant studies. Oh yes, at 210x Venus appeared about the size of the Moon unaided - which in turn is about as large as the Red Planet gets during a close opposition. This is not the kind of image scale I prefer!
Speaking of Mars - due to The Incredible Shinking Planet's "shrunken" state, made no effort to track it down this evening.
Not speaking of Mercury - no effort here either.
Speaking of apparent size - anybody notice that Jupiter is losing much of its former grandeur? In fact, the planet at 210x is now about the size seen at 180x during opposition. And "smallish" 180x views of Jupiter were why I bought a barlow lens in the first place! Again image scale. I like it. Sure Jupiter looks nice and crisp at 150x. But have you ever viewed the planet at 540x? It's about the size of a quarter held at a distance that just allows you to read the print. Incredible image scale - but rarely feasible through Argo. And the kind of magnification most experienced observers would think laughable...
Can you see significant detail on Jupiter at 540x? Sure, in fact such a magnification may be used for the same reason that 200x is while viewing bright galaxies - to dissolve low surface brightness detail and make discrete details more evident to the eye. On Jupiter this works too - but generally only while observing the NEB. This night however, under marginal stability, made no effort to achieve "image scale" of this magnitude. For Backyard Boulder Creek still has "Spring Fever": 6/10 stability at best, 7/10 early and just before the local "heat engine" kicked in...
And with Jupe still well within the skies middle-third, immediately caught an ingressing GRS. Stability good enough to reveal the EB (faintly), NEB belt edge irregularities, a condensed NTB, and both frontiers of the STB. In addition, the NPR showed various albedo shadings, and a single white oval could be just seen egressing twoard the leading edge of the planet on the NEB. Decent but not a "knock your wool-socks off" view.
Didn't really spend much time on Saturn. It's a shame what low sky position has done to such a finely-hewn planet. Cassini and SEB, though detectable, were both vague. Posterior ring shadowing lacked any sense of "dimensionality". Probably time to let the Ringed Wonder slip into the Sun's glare. But nah, there does remain the hope and the possibility of one more well-chiseled view before the parting of the ways. And of course, after that you can always hope for one more...
It was time to follow the emergence of Polaris-B. Now before you all laugh at me, let me remind you how difficult it can be to orient an equatorially mounted scope on the Pole Star. Then also let me mention that, during dusk, it is very difficult to tell one star from another through the finderscope - especially one that lacks a perfectly flat field. Having said all this, you must know what happened... I slewed the scope north, centered on a "bright" star, and sat there admiring the fact that occasionally "Polaris" would actually sport a first diffraction ring! Why the seeing must be better than I thought! Half an hour later, and with only the vain imaginings of an "extinction-level" Polaris B behind me,gave up and reflex-sighted Argo on the real Pole Star! And even at 210x, under marginal seeing, there was the companion. So too late to accomplish what I had hoped to.
Thus my plans for the evening were mostly blown. For you see, I'd hoped to record the time at which Polaris-B could be first held under various magnifications. The idea being that difficult disparate pairs have a narrow range of solvable magnifications. Such a magnification appears to be a function of primary brightness, pair separation, and magnitudinal delta. Along with the darkness of the sky and presence of intervening thin clouds.
Let me illustrate: Say you want to resolve Sirius B. Well, we all know that Sirius A is tremendously brilliant and usually overwhelms its dim 8th magnitude dwarf companion. But since the secondary is some 8 arcsecs or so distant, there must be some strategy to improve your chances!
Obviously, you want the stillest possible sky. Then, surprisingly (in Sirius case) you may want a relatively "bright" sky. Why? Because a bright sky (or thin clouds) helps "suppress" the flare and light play of the primary and gives the eye a better chance of discriminating the more pointillistic light of the secondary.
Of course, another variable is aperture. But how much is enough? Any scope can resolve an 8 arcsec pair, right? But what is needed is a scope that can somehow reveal 8th magnitude stars through a dusky sky. One that is typically just dark enough to find Sirius unaided. But most scopes aren't able to do this. You've effectively got minus 1 magnitude sky transparency. You need to go some 9 magnitudes deeper with your scope. For this, quality aperture is a must, along with a well selected magnification.
In observing numerous disparate pairs, I've found that too much magnification diffuses the secondary and makes detection difficult. Too little magnification fails to darken the sky enough to reveal stars of that magnitude. Thus the quandary, and why I was willing to sit there at the eyepiece not-following Polaris-B's emergence at a variety of magnifications.
And what a fine study our Pole Star is in this regard. Most scopes will reveal the faint secondary at large exit pupils. This as soon as you can find it in the night sky unaided. But try finding it under high magnification under the same conditions - especially through an unstable atmosphere! So tough, on-the-edge disparates, are magnification-dependent.
As a result the rest of my evening was pretty much a wash out. There was no base-line of magnifications over time to make reference to. But dutifully, I turned up each unresolved double from the original Spring list. Almost everyone of which showed something I know not what at various position angles which often failed to map against published data. Meanwhile, I could also easily delude myself into thinking I saw "faint blue" secondaries even at varying separations and position angles for a single star!
But to be complete, here's the "skinny" on the various "on the edge" pairs observed:
Name Star RA Dec Comp Mag1 Mag2 Sep PA U2000 Spec Notes
URSA MINOR:
KU 1-AB 16 43.0 77 30 AB 6.1 9.4 2.7 184 11 F2 ALSO HU 917
Faint secondary trailing to north, separated by about 5 arcsecs. PA does not match (should lie south), but there is always some doubt concerning data posted on the web (or especially out of books!). Secondary difficult at 210x. More definite at 120. This one should be solvable and only needs higher sky position for confirmation.
URSA MAJOR:
STT 521 UPSILON UMA 09 51.1 59 03 3.9 11.5 11.3 295 45 F0 A is a Delta Scuti-type var.
Something very faint and to the south. This PA does not match published data. But it is a long-period probably line of sight pair. This one should also be solvable but will take a very special night!
HJ 2477-AB IOTA UMA 08 59.3 48 02 AB 3.9 9.5 4.5 24 70 A5 AXBC: Orbit calc\'d. A is a Delta Scuti var and sp-bin.
Occasional 120x glimpses of something faint trailing and slightly north, distance about 5 arcsecs. PA matches but needs confirmation. This is the one I hope to focus on over the next few weeks. Clean resolve or bust! To resolve unambiguously would roll back Argo's "threshold of detection".
STT 199-AB 09 20.7 51 15 AB 6.1 10.2 5.7 133 44 F2
A no confidence illusory "companion". This one about 8 arcsecs trailing slightly south. Due to non-use of setting circles, not sure if I've even located this pair yet. And due to my propensity for seeing phantom secondaries "trailing and to south", no confidence!
HO 377-AB 51 UMA 11 04.6 38 14 AB 6.1 12.6 8.2 250 73/ 106 A2
Secondary much too faint under the circumstances. But I could see it if I really wanted too!
BU 919 11 59.3 33 09 6.0 12.0 4.5 16 107 K0
Another "phantom secomdary". This time due south at about the right distance. Due to separation - about as likely as HO 377 above...
LEO
STT 523 39 LEO 10 17.3 23 06 5.8 11.4 7.6 299 144 F5 Mt. Wilson spectral types are F1s and dM1.
Another phantom that trails slightly south. PA matches but not able to "hold" anything - despite extreme aversion. This pair would constitute a breakthrough as well.
BU 105-AB KAPPA LEO 09 24.6 26 11 AB 4.6 10.4 2.4 211 143 K0 Y/B
If anything, leading slightly south at 180x. At one-hundreth the primary's brightness, 2.4 arcsecs is probably well beyond Argo's capabilities. This one probably needs a large "research-grade" scope from a fine observing site.
KUI 54-AB CHI LEO 11 05.1 07 20 AB 4.7 11.0 3.6 268 191 F0
Nearby foliage prevented me from observing this very difficult, but potentially solvable disparate. Like Iota UMA, I'll stay after this one! Like many of the others in this report would establish a new "line drawn in the sky".
STF 1536 IOTA LEO 11 23.9 10 32 4.1 7.3 1.3 141 191 F5 "P = 192 yr., a = 1.92'', motion retrograde."
Conditions did not support resolution of this pair at magnifications used this evening (70, 120, & 180x). A clean resolve indicates excellent seeing. Stars of this type are valuable for assessing seeing conditions. (Very much springtime's Delta Cygni.)
STF 1552-AB 90 LEO 11 34.7 16 47 AB 6.1 7.4 3.4 208 147/ 192 B3 B is a sp-bin. W/B
Elongated with secondary trailing to south at 180x. Definitely tighter than the 3.4 arc secs sighted above. Also on my "short list" for continued monitoring. There is such a variance in observed separation that it warrants micrometric measurement! Or is there another double in this region?
Meanwhile as I fruitlessly tracked down one double after another, a perfect deepsky opportunity passed overhead. Stars visible down to nearly magnitude 5.5. This sky was meant for galaxies - the Galaxies of Spring. How could I possibly ignore them? Perhaps because I will never resolve those "on the edge disparates" during a lunation. They need dark and steady skies. And so do I...
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A Definitive Night Out
Once again last evening (Wednesday, May 1) clouds dominating the daytime sky rolled away and I had a solid night of observing. And even more importantly the "spring fever" of the last few weeks subsided and sky stability returned to the usual 7+/10 seen most nights here in the Santa Cruz Mountains.
Evening started early. By 8:15, with Argo well-chilled and no sign of tube currents, easily picked Venus out of the western dusk. Planet showed the typical luminosity gradient. Again, some 30 degrees supra-horizontal, no real atmo-chromaticism. Interestingly, despite my best efforts to bring the planet to focus, found that once I shifted to a well-positioned Jupiter had to refocus. So stability in that part of the sky less than 5/10.
Jupiter however, lay well within the sky's middle third. At 210x quite sharp. Aside from the usual compliment of belts (xEBs, xTBs, xPR-shading) caught a huge white oval just past the CM on the NEB. Also several reasonably contrasty NEB incursions into the EZ. For some reason, didn't catch the SEB rift until I bumped the magnification to 360x. Made a check at 540x too! White oval difficult but could still made out along with the EB and belt edge irregularities. Aesthetically the planet looked best at 210x. Slightly better views of discrete details at 360 however.
Saturn now lies no more than 10 degrees east of Venus along the ecliptic. Cassini appeared an "unsharpened pencil line". SEB's northern frontier relatively distinct while the south blended into the temperate region. Shadowing effects though obvious, lacked presence. So maybe 6/10 seeing in that part of the sky.
Had hoped to follow Polaris-B's emergence at various magnifications. But as a result of steady skies found that every magnification revealed the companion as soon as I tracked the pair down (around quarter to 9:00PDST). The companion however was clearly sharper at lower magnifications than higher. Meanwhile the background sky was significantly darker. Overall the edge - to my eye - leaned towards the lower magnifications.
Speaking of higher magnifications - able to resolve Polaris-A airy disk this evening. However, the diffraction ring appeared less than text book. Airy disks were quite nice throughout the evening. For instance while viewing 3.9 magnitude Upsilon UMA, actually caught the first diffraction ring in perfect concentricity and equi-luminosity. Beautiful! Must have been a rare moment of 9/10 stability. (The fourth harmonic was also visible as a "ghostly presence" - something that only appears on very dark and steady nights.)
After monitoring Polaris, went on to a well-placed Iota Leonis. Inspected the pair under a variety of magnifications. Found I could get better than hairline separation at 180x while 120x showed pair-elongation. Although this is a little out of range for sepCalc, the values suggest the pair is at minimum 1.2 arc seconds separated. Meanwhile at 360x, I could plainly see the blue-white secondary trailing to north just outside the first diffraction ring. Since the first diffraction ring lies at roughly 170/Dmm (D=aperture) from the center of a star's airy disk, this method also suggests a separation of about 1.2 arcsecs. So yah, no wonder this particular disparete double (magnitudes 4.1/7.3, published separation 1.3) requires 6+/10 seeing to resolve!
While in the neighborhood, swung north to 90 Leonis. Immediately identified the pair based on a distant 11th magnitude come due north. Like Iota, this double resolved cleanly at 180 and elongated at 120x. Again like Iota, the pair gave a fine resolve at higher magnifications (210 - 540x). And as previously, position angle (trailing to north ~70 degrees) is quite a bit awry from the published 208 degrees. Meanwhile, the separation has narrowed significantly as well.
By the time I observed my next pair, the sky had darkened considerably. 5.3 magnitude SAO 81054 (located between Epsilon and Mu Leonis) could just be held direct. And this was a very good thing too! For Chi Leonis (mags 4.7/11.0, sep 3.6, PA 270) proved to be a very difficult but satisfying resolve, One that was characteristic of an "on the edge" disparate.
First off, 70x magnification kept turning up a variety of "phantom secondaries". Meanwhile, 120x showed nothing suggestive of a companion. 180x was a bit more promising while at 210x the 11th mag companion was suspected. This was also true of 540x. Only 360x gave a confident view of this extremely faint and relatively close companion. Yowser! There's real food for thought here! Under 7/10 stability, and 5.3 ULM skies at 360x, Argo's calculated telescopic limiting magnitude is roughly 13.6. Meanwhile, some 3.6 arcsecs from a 4.7 magnitude star the glow is so intense that an 11th magnitude star can just be detected with any confidence. Finally 540x magnification was not supported by sky conditions (causing the secondary to "dissolve" under 7/10 seeing). So its obvious you can't just throw magnification at these babies and expect resolution...
Also took in three doubles in Ursa Major tonight. Neither Upsilon (mags: 3.9/11.5, sep: 11.3, PA: 295) nor Iota (mags: 3.9/9.5, sep: 4.5, PA: 24) gave any hint of a secondary (despite whatever magnification I through in their general direction). However, I did revisit Nu (mags: 3.7/10.1, sep: 7.3, PA: 147) to get a sense of how various magnifications effected this widely disparate pair.
Once again, was able to pick out Nu's companion at the expected PA (trailing to south), but only at magnifications in the range 70 - 210x. In fact, the best view was at 120x, while at 70x the secondary to "jump about" a bit and higher magnifications appeared to increase the intensity of the 3.9 magnitude primary's "glow". The fact that there remained at least some range of available magnifications suggests to me that an even dimmer secondary may have been seen at this separation. However - not much dimmer!
Now tonight was not all about doubles! In fact I had selected three galaxies from the 6 inch optimal aperture list (M81, 82 & 51) for review at a variety of magnifications (70, 120 & 180x). The idea was to get a sense of how the peculiarities of image scale and magnitudinal reach impacted unresolvable studies of variegated surface brightness.
M81: At 70x, this large 2:1 aspect ratio galaxy (magnitude: 6.9, size: 20x9) gave a fully averted appearance of about 1/3rd the 45 arcmin field in major axis extension. So maybe 15 x 6 arcmins of the spiral was detectable. In terms of structure, a starlike nucleus, bright core region, and diffuse spiral extensions were seen. Bumping the magnification to 120x, revealed a secondary condensation half-way out from the nucleus to the west. At 180x, the core region became visibly spheroidal with perhaps a better defined eastern hemisphere. Skies were at best 5.0 ULM deep in the northern sky over Boulder Creek proper.
M82: At 70x, the irregular nature of this edge-on presented galaxy was instantly apparent. The galaxies primary condensation lay offset decisively to the east. The galaxy's southern frontier appeared visibly sharper. It's western extension appeared far more developed than that to the east. It's major axis appeared to displace maybe 1/7th the 45 arcmin field (or about 6 arcminutes in length and 2 arcmins in width).
120x didn't seem to do more than make the irregular profile of the galaxy more obvious. Interestingly, the galaxy now seemed to take up about 1/5th the 26 arcmin field along the major axis. So not a whole low more of the galaxy was "dissolved" in the process of magnification.
At 180x the ideosyncratic nature of the galaxy's profile revealed itself as a triumvirate of condensations along its profile. The vaguish core region resolved to an almost starlike node. This nuclear condensation was in turn echoed by two others. The one to the east appeared closer to the nucleus than that to the west. Meanwhile, the western condensation appeared visibly brighter than its eastern confrere.
The last study for the evening was M51 in Canes Venatici. But by this time, the sky had taken on that "gauzy" look that discourages extended time at the eyepiece. At magnitude 8.40 and apparent size: 9x8'. M51 took up about 1/7th the field of view at 70x. So maybe 6x5 armins of the galaxy were seen. And this 6 arcmins appeared visibly more overdeveloped to the west than the east. At 120x, a 13th magnitude "star" appeared maybe 3 arcmins southwest of the galaxy's starry nucleus. A "sense" of spiral was possible W-N and E-S. By 180x, the core rgion took on an "oblique" appearance as the roots of the spiral extensions revealed themselves.
Now the fact is that on at least one occasion, M51's spiral arms have been detected through 150mm Argo at 210x - along with various knots and condensations. But conditions must be very good to achieve the kind of contrast needed to achieve such a view.
Of course, there is another way to get such a view, but that would involve contracting a illness I'd rather avoid - "aperture fever"...
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Wrapping Things Up?
Just after my return to observing the night sky, I came to the conclusion that without a definite series of astronomical projects to pursue, my interest in the hobby would soon flag. Fortunately, there are no lack of such projects available to the avid amateur. Among those I've taken "to heart and mind" is the pursuit of "on-the-edge" observation of double stars.
There are in fact two areas of extreme duplicity that I personally tend to favor. One are the "sub-Dawesian matched pairs" class of doubles. While pursuing that line of investigation, ran into a wall somewhere between .55 arc second Beta Delphinus (magnitudes 3.6&4.6 .55") and .5 arcsec Gamma Andromeda C. It certainly would appear that no matter how much magnification you throw at ever tighter matched pairs, you eventually fail to detect elongation suggestive of duplicity. Thus a value of about 80/Dmm (D=aperture) may very well describe the frontier beyond which even the finest of scopes fails to reveal duplicity in matched double star pairs.
In the matter of disparate doubles (defined as pairs whose delta is greater than 1.5 magnitudes), the ability to state a hard and fast limit is exceedingly problematic. In general, the main limiting factor for matched pairs (outside of scope and observer) appears to be seeing stability. While that of disparates adds sky transparency to the mix as an essential factor and places far greater load on the refinement of the optics (freedom from glare and the ability to present high contrast views). Add to this careful selection of magnification on the part of the observer (as discussed earlier in this series) and you can see why resolving doubles of this type is such an intense challenge!
On the basis of this last series of observations, I've now "rolled back" my personal threshold of disparate double resolution along several fronts. Without making an exhaustive search of all observing records, it seems that the Nu UMA pair (magnitudes 3.7&10.1, separation 7.3") lies just this side of "no pairs land" in the 5 to 10 arcsec separation range. Meanwhile between 2.5 to 5 arcsecs, Chi Leonis (mags 4.7/11.0, sep 3.6") takes a similar post. Among disparates which include sub-3.0 magnitude primaries, the summer pair Eta Draconis (magnitudes 2.9&8.2, separation 4.8") proved difficult but probably surpassable. While the toughest pair at or near the first diffraction ring (Rayleigh's limit), Iota Leonis (4.1/7.3, 1.3") is also likely to be superceded as observations continue. Finally, right at Dawes limit (here defined as 120/Dmm), several mildly disparate pairs (delta=1.5 magnitudes) have proven resolvable in the past. These have alwaysrequired magnifications in the range 360 - 540x.
Of course, given the fact that "there will always be a better sky around the corner", it is unlikely that "the quest for the disparate doubles edge" will ever be consummated.
Just the kind of thing to keep me at the feet of Nuit for a lifetime!
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