. There I was,
. looking for something new
. to do,
. when I ran into
. Nu-1 and Nu-2.
. And not just once, but twice!
But I suppose I should explain before the guys in the white coats get here . . . . . . .
It was one of those cursed dark and stormy nights – again. In fact, it was like November in May: rain pounding on the roof so hard it almost echoed inside the house; over-sized drops of water throwing themselves madly at the wooden planks of my deck, spreading out on impact like the shock waves of a supernova; and water rushing down the streets in torrents that threatened to turn into rivers wide enough to float barges of grain. And above it all, a constant howling wind that somehow had broken the shackles of its winter chains and escaped into late spring.
So longing for a calm, clear, dark, and storm-less night, I picked up my well-worn copy of Sky & Telescope’s Pocket Atlas and began looking for future telescopic targets. I was searching for new horizons, sights to stir the soul, un-tracked trails in the vault of wilderness beyond the storm clouds – in fact, anything to turn my thoughts away from the relentless rain. And fortunately for my water-soaked sanity, I quickly found what I needed.
There it was, on chart number fifty-two, parked a few degrees west of the Hercules keystone — barely beyond the Herculean border in fact — arrayed one above the other in Corona Borealis: Nu-1 and Nu-2. Or as Hipparchus might have referred to them if he had been peering over my shoulder at the atlas, ν1 and ν2 .
As my eyes roamed over the surrounding stellar terrain, they were drawn to another pair of Nu’s. These were also barely beyond the Herculean border, this time in Boötes, unlikely as that may seem. In fact, they’re wedged into an angle formed by the western edge of Hercules and the northern corner of Corona Borealis, parked on a shelf as it were. And unlike the prior pair, they’re arrayed side by side – or at least they are on the chart (number fifty-three if you’re following along).
I breathed a loooooong sigh of relief, launched myself into a frenzy of stellar research, and ignored the rain as it ran riot outside my windows.
Now one of the more admirable traits shared by the two pairs of Nu twins is you can soak up the splendor of their photonic beauty with a mere fifty millimeters of aperture. In fact, they even qualify as outstanding and easily separated binocular binaries. But if you have more aperture, by all means bring it along – it’ll come in very handy before we’re finished.
Now this may seem complicated, but it’s not really. First I’ll list the basic data for Nu-1 and Nu-2 separately, and then I’ll add the table with separations and position angles of the individual components:
Nu-1 (ν1 ) (20 Coronae Borealis) (Σ I 29, or STFA 29) HIP: 80197 SAO: 65257
RA: 16h 22.4m Dec: +33° 48’
Distance: 556 Light Years
Spectral Classification: M2
Nu-2 (ν2 ) (21 Coronae Borealis) HIP: 80214 SAO: 65259
RA: 16h 22.5m Dec: +33° 42’
Distance: 545 Light Years
Spectral Classification: K5
In the data below, Nu-1 is the “A” component, Nu-2 the “B” component
Designation Magnitudes Separation Position Angle WDS
AB (STFA 29) 5.39, 5.58 365.60” 164° 2011
AC (HN 81) 5.39, 11.30 68.10” 241° 2002
AD (STFA 29) 5.39, 12.90 277.10” 153° 2002
BE (H VI 18) 5.58, 10.20 100.00” 16° 2002
NOTE (July 2014): See update on WDS identifications, which is further down the page (just prior to the Boötes discussion).
If you’re using a 50mm or 60mm scope, or binoculars, you’ll find your attention is drawn immediately to the “A” and “B” components, Nu-1 and Nu-2. If you’ve got more aperture, probably at least one hundred millimeters worth, you’ll be able to pry loose the “C” and “E” components. “D” is another story entirely, which we’ll get to later.
To get started, here’s the view through my 50mm Zeiss refractor:
The primary and secondary, Nu-1 and Nu-2, are aligned pretty close to a north-south axis. Nu-1 is the northernmost of the pair and is positioned slightly to the west of the more southern Nu-2 — and Nu-1 has staked out a claim on most of the companions. In order to extricate them from the darkness, though, you need a bit more than a 50mm refractor. I used a 9.25 inch SCT to view them, but as I mentioned earlier, you should be able to catch the AC and BE pairings with a minimum of a hundred millimeters.
Here’s the mesmerizing view I found in the SCT on the night after the sketch above was made:
Once again, Nu-1 is on the north side of the sketch, and just below it and slightly south of west you can see the 11.30 magnitude “C” companion. The 10.20 magnitude “E” component, which is linked to Nu-2 (the “B” partner in this pair), is visible above it in the sketch, or just slightly east of north.
So where did “D” go? At a distance of 277.10” from Nu-1 (“A”), even at a magnitude of 12.9 it should be visible in a 9.25 inch SCT.
After pinning down the “C” and “E” companions on my first visit to the Nu twins, I did some mental comparing of the separation between Nu-1 and Nu-2 (AB = 365.60”), Nu-1 and “D” (AD = 277.10”), and Nu-2 and “E” (BE = 100.00″), and quickly came to the conclusion that “D” was actually at about the same distance from Nu-1 as the “E” companion is. Again, with a bit of mental magic, I could also see the position angles of AD (153°) and BE (16°) almost overlap at the respective distances of AD and BE.
And sure enough, when I turned to Vizier to diagram them, that’s what I found:
In fact, it looks as if “D” and “E” are virtually occupying the same position. (For a tutorial on how to use the software in Vizier to plot position angles and separations, see this article in the April 2013 issue of JDSO).
I enlarged a photo of the area, which is basically the positive image of the negative one used for the Vizier plot, and came up with this result:
The arrow I inserted is pointing at what might be “D” – but it could also simply be an artifact of the photographic process.
Brian Mason at the US Naval Observatory (the same folks who bring us the indispensable Washington Double Star Catalog), was kind enough to supply me with the observational data for all of the components of Nu-1 and Nu-2. There are five observations of AD recorded in the WDS data, ranging from 1913 to 2002, which show little variation. The separation runs from 281.73″ in 1913 to 277.11″ in 2002, and the position angle from 154.3 degrees in 1913 to 153.3 degrees in 2002. “E” shows very little motion as well — the first observation listed for it in the WDS (1879) shows a separation of 104.56″ with a PA of 15.6 degrees, again not much different than the most recent 2002 observations of 100.01″ and 15.9 degrees.
At this point, I turned up some very interesting details. The 1879 observation of the BE pair was made by S.W. Burnham, and from what I can determine, he was using his six inch Clark refractor, which would seem to explain his not detecting the “D” component. The initial 1913 observation of “D” was made by William Doberck, and after one heck of a lot of research, I discovered he was also using a six inch refractor based in his observatory in Sutton, England. If you click on the thumbnail at the right, you’ll see four observations recorded for the AD pair, which is labeled there as BC. Those four observations were averaged to yield the result shown in the last two columns at the right (in the red box), which match the data listed in the WDS. And if you look closely, you’ll see the four observations were made at a magnification of 150x. (!)
Note that there is no magnitude listed there for any of the stars. If it wasn’t for the fact that the WDS lists separate magnitudes for the “D” and “E” components, I would be tempted to say both designations are referring to the same star. At any rate, based on the accumulated store of data, it certainly appears that “D” is really there, buried in the glare of the 10.2 magnitude “E” component.
Before we move on to Boötes, if you look at the data above for the Nu twins you’ll see two of Sir William Herschel’s catalog numbers listed under the designation column. He discovered H VI 18, the BE pair, on July 30th, 1780, and described “B” as “red” and “E” as “garnet.” (p. 152 of 1782 Catalog in Philosophical Transactions, Vol. 72, 1782). In the case of the AC pair, which he designated as H N 81, he made a total of three visits: May 28th, 1791; March 20th, 1795; and March 22nd, 1795 (page 22 of the 1821 catalog, no longer available on line).
Update: As of July, 2014, the BE listing in the WDS has been changed to BD and the “E” designation has been dropped — in other words, there are four stars in the Nu CrB system, not five. It turns out “D” and “E” actually referred to the same star. The key to discovering that was the realization Doberck had reversed the designations for Nu CrB “A” and “B” — his “B is the WDS “A”, and his A” is the WDS “B” . . . . . . . . which meant his BC is the WDS AD . . . . . . . . . and his AC should have been labeled BD in the WDS instead of BE. If that sounds confusing, it’s because it is. Steve Smith and I have combined to write a paper for the JDSO (Journal of Double Star Observers), which can be found at this link. At any rate, here’s the updated data for Nu Coronae Borealis as of July, 2014:
Designation Magnitudes Separation Position Angle WDS
AB (STFA 29) 5.39, 5.58 354.70” 164° 2011
AC (HN 81) 5.39, 12.62 68.10” 241° 2002
AD (STFA 29) 5.39, 11.53 277.10” 153° 2002
BD (H VI 18) 5.58, 11.53 100.00” 16° 2002
OK — let’s leap over to Boötes now and see what’s Nu. If you look at the chart above (you can open it in a separate window here), you’ll find Nu-1 and Nu-2 Boö sitting at the northeast tip of a line drawn from Delta Boötes through Mu Boötis (Alkalurops) and extended another four degrees beyond.
Nu-1 (52 Boötis) HIP: 75973 SAO: 45580
RA: 15h 30.9m Dec: +40° 51’
Distance: 872 Light Years
Spectral Classification: K5
Nu-2 (53 Boötis) HIP: 76041 SAO: 45590
RA: 15h 31.8m Dec: +40° 54’
Designation Magnitudes Separation Position Angle WDS
AB (A 1634) 5.80, 5.80 0.05” 32° 2010
AB, C (Bu 1450) 5.10, 13.00 93.50” 88° 2002
AB, D (KZA 97) 5.10, 13.00 119.90” 319° 2002
Distance: 430 Light Years
Spectral Classification: A5
And the first thing to notice here is Nu-1 and Nu-2 are not cataloged as a related pair, which is not surprising considering they’re 442 light years apart! Nevertheless, they make an enticing pair of stars for binoculars or a 50mm refractor:
And the second thing that should jump out at you from the data above is the offspring of the Nu-2 family are just a bit on the difficult side to catch sight of. We’ll skip the AB pair (you would need equipment none of us have to split it), and instead focus our attention on the two thirteenth magnitude companions, “C” and “D.”
Let’s first take a look at Nu-1 and Nu-2 in a 50mm scope:
You need a moonless sky to see the orange-ish K5 tint of Nu-1 in a fifty millimeter lens, but if you compare it closely with Nu-2, you’ll see the difference. I was even able to detect the color differences in my Canon 10×30 IS binoculars with careful scrutiny (while I was lying flat on my back on my deck!).
If you recall our earlier fifty millimeter view of the Nu twins in Corona Borealis (easy to do – just click here), you’ll see the Boötes pair are a bit further apart. To be more precise, the pair in Corona Borealis is separated by a distance of six arc minutes, while the Boötis duo has almost eleven arc minutes of intervening interstellar space wedged between them. Of course, that eleven minutes of arc is actually the 442 light years of separation referred to a few paragraphs above, which is perfectly undetectable even to our telescopically aided but three-dimensionally challenged eye.
We’ll switch over to Nu-2 now, aka 53 Boötis, and see what we can see of the two thirteenth magnitude companions arrayed to the east and northwest of the primary. But for this, you’re going to need six inches of unobstructed aperture. It might be possible to glimpse the faint photons of “C” and “D” in a five inch refractor, but you’ll need dark skies devoid of the oceanic moisture I battle with on most nights . . . . . . .
. . . . . . . which is exactly the problem I faced when I attempted to dig those two stars out of the glare and scowl of the 5.80 magnitude AB alliance. With persistence and penetrating visual perspicuity, though, I got ‘em – but to give you an idea of their difficulty, let’s first look at a sketch without the gray-white glow and glare:
But enough of pretending and wishing for what isn’t likely. Here’s reality:
And that’s just about the most realistic portrayal I’ve ever managed to coax out of a computer program! It was every bit as hard as all that to catch sight of those two thirteenth magnitude wisps of light — it was averted vision all the way down. The “C” companion was noticeably more difficult to extract from the primarial glow, which is quite consistent with its being twenty-six seconds of arc closer than “D.” The unrelated thirteenth magnitude star to the south of the primary, which was an unexpected bonus, was about midway between “C” and “D” in difficulty.
So there you have it – two Nu pairs of stars to grace the lens of a small aperture telescope that also offer additional opportunities for those less aperture-challenged. But there’s more to be had in the vicinity of both of these pairs of stars, so we’ll hang around in both Boötis and Corona Borealis a bit longer. I’ve got a few more tours planned, so don’t wander away . . . . . . .
. . . . . . and Clear Skies! 😎