There I was, flushed with the all-knowing adolescent over-confidence that comes with being a month away from entering the grand halls of high school (eighth grade!), stuck in Texas where-I-absolutely-didn’t-wanna-be with my vacationing parents, and suddenly I was tumbled head over heels by the blonde daughter of my aunt’s next door neighbors. Tanya was her name. She was a year younger than me, blonde and beautiful, and had a Texas twang that transformed every millimeter of me into a heap of helpless mush. I still remember the dark night we stood outside, awed by the stars, as my heart was trying to break loose from its moorings.
And yes, I still remember those west Texas stars, too. It was August, the skies in those days were black, black, black, and there were more stars on display than I had ever seen in my entire life. For some reason I remember being mesmerized by the fish-hook shaped outline of Scorpius, even though I was only vaguely familiar with any of the constellations at the time. More than likely it was the deep red-orange glow of Antares that drew my eye, pulsating as hard as my heart was throbbing.
Tanya and Texas and the stars. Every time I look up at Ursa Major my eyes are drawn to the pair I always thought were named for her, Tania Australis and Tania Borealis. Of course, that isn’t quite the case. The Arabic Tania means “second,” which refers to the three feet of the Great Bear, but I’ll defer to Jim Kaler’s explanation of that for now, which can be found at either of the two prior links.
The Tanya I knew hardly struck me as “second”, and neither are the two stellar Tania’s – each is a beautiful star in its own right. The northern one (which is what Borealis means) is a vibrant white star (spectral class A2) that almost turns its surrounding neighborhood to daylight when captured in an eyepiece, and the southern one (Australis means south) is a stunning reddish orange (M0) sun that I find as impossible to resist as the real Tanya was. The only thing better than each one seen individually is the pair of them beaming with demure delight in the eyepiece of an 8×50 finder.
But since I’ve got a pair of star hopping adventures planned around these two stars, let’s locate them so we can get down to work before we lose this dark night to a sudden invasion of star devouring clouds:
ENG 43 HIP: 50505 SAO: 43279
RA: 10h 18.9m Dec: 44° 03’
Magnitudes: 6.73, 9.37
Position Angle: 97° (WDS 2002)
Distance: 67 Light Years
Spectral Classification: G5, G0
This is one of the wider pairs we’ll look at on this tour, so take some to enjoy the view. You’ll need to narrow your eyes quite a bit on the next two since the separations will become progressively tighter, but your diligence will be rewarded on the last pair (and no skipping ahead – the Sky Gods are watching).
I had a couple of quick views of ENG 43 in both a six inch refractor and a C9.25, but since they were far more aperture than necessary for this pair of stars, I decided to call the 100mm f/13 Skylight from its perch in the house in order to commit its view of these stars to posterity. It was one of those nights when there was a brief window of opportunity, so I had to sketch fast, a task made more difficult by a thick murk of moisture in the air which swallowed about a magnitude’s worth of light. So the view in the sketch might be more similar to what would be seen in an 80mm refractor on a good night, but the essentials are still there at least.
Down in the south corner of the field you can see eighth magnitude POP 117, a pair of 8.3 and 9.6 magnitude stars separated by a miserly 0.8 seconds of arc. I passed on those since they were out of reach even on a good night with a four inch refractor, but be my guest. The POP refers to G. Popovic, who discovered this pair in 1976.
If you look up the ENG prefix, you’ll find it now refers to Engelmann, but at one time it was used to designate the discoveries of Dr. B. von Engelhardt (page 351, under Dresden), who operated a private observatory in Dresden (Germany), using a twelve inch Grubb refractor. It was he who actually discovered this pair of stars in 1893. More on the prefix change can be found in the WDS “References and discover codes” if you scroll down to ENG.
Σ 1427 HIP: 50766 SAO: 43306
RA: 10h 22.0m Dec: +43° 54’
Magnitudes: 8.18, 8.54
Position Angle: 214° (WDS 2012)
Distance: 437 Light Years
Spectral Classification: Both stars F5
Half a degree east from ENG 43 you’ll find an eighth magnitude star that divides easily into two barely separated stars when placed within the circular confines of a medium powered eyepiece.
I stayed with the Skylight 100mm for the sketch of this pair, but I’ve also viewed them in a six inch refractor and a 9.25 inch SCT. You certainly get a better feeling for the colors of these two stars in the larger scopes, but I prefer the tighter and more delicate jewel-like view displayed in the 100mm scope. Both stars radiate a light yellow that occasionally flashes hints of gold at you. This pair, by the way, was discovered in 1829 by Herr von Struve.
Now, back to our second chart above, which is more handy if you click on it here and open a second window. With Σ 1427 still centered in your finder, if you look closely, you’ll see a dim triangle of stars that starts two degrees to the northeast. HIP 51290, a 6.35 magnitude sun, holds down the northwest corner, 7.35 magnitude HIP 51603 occupies the southeast corner, and sitting another degree northeast at the peak of the triangle is our goal, Bu 1074, shining its wan orange light at a magnitude of 7.2. Center it in your finder and sharpen your visual apparatii!
Bu 1074 HIP: 51846 SAO: 43396
RA: 10h 35.5m Dec: +45° 39’
Magnitudes: 7.2, 11.2
Position Angle: 206°
Distance: 510 Light Years
Spectral Classification: K2
And what we have here is another compact package passed down to posterity by that shrewd disciple of the difficult, S. W. Burnham. I say that because if you look closely at the data line above, you’ll see we’re dealing here with four full magnitudes of difference, which means the secondary is forty times fainter than the primary. And when you factor in the very close proximity of that secondarial light to its primarial parent, and then toss in the comparatively weak magnitude of the secondary, you suddenly discover you’re adrift in the vague and nebulous terrain of the difficult . . . . . . . which in plain language means this ain’t gonna be easy.
And it wasn’t.
I needed several nights to scrutinize these twin suns of the interstellar medium, mainly because I couldn’t be sure my eyes were seeing what they thought they were seeing. My weapon of choice was my six inch f/10 refractor, and the best I could eke out of the totally uncooperative seeing conditions was an averted vision view, which is shown in the sketch below:
I finally managed to pin the secondary down with direct vision in a 9.25 inch SCT on a night of improved seeing. A mere puff of light is what it was, every bit as difficult to see in the eyepiece as it is in the sketch above. I even had to hold my breath to avoid blowing it out (barely an exaggeration), which left me wondering how in the world the eagle-eyed Mr. Burnham was able to measure the separation and position angle.
Update 4/22/2017: It’s no wonder I had to hold my breath, as the image of BU 1074 at the right taken by Mark McPhee illustrates quite clearly. Even after slightly enhancing the image, the secondary is barely there. Judging by the relative size of the secondary to the primary, I would wager an orphaned eyepiece on the proposition the secondary is a full magnitude fainter than the 11.2 shown for in the WDS. I just checked the URAT1, GAIA DR1, and UCAC5 catalogs, but none of the three were able to detect the secondary hiding in the glare of the primary. So for the time being, that mystery remains to be unraveled. Note that east is at the left in this image, north at the top.
At any rate, it was only after all my vision-vexing effort had taken place that I thought of looking up Bu 1074 in Burnham’s A General Catalogue of 1290 Double Stars. For some reason my mind had leaped to the unfounded conclusion that Burnham had discovered this star with his six inch refractor. Instead, what I found accompanying his 1889 discovery on page 110 was this notation:
“Discovered with the 36 inch.”
Which explains why I thought I heard laughter on the nights I was puzzling over this thing.
Not funny, S. W. Not funny.
But as a reward for going above and beyond the call of the sane and simple, how about something a bit more relaxing for our worn-out optical orbs now? Feast your eyes on the separations listed below:
SMA 75 (AB is HJL 130, also SHY 216)
HIP: 52469 SAO: 43444
Magnitudes Separation Position Angle WDS
AB: 5.21, 7.35 288.40” 88° 1874/2012
AC: 5.21, 11.11 150.30” 15° 1907/2002
AD: 5.21, 9.18 382.20” 45° 1958/2012
BD: 7.35, 9.18 261.40” 356° 1907/2002
BP: 7.35, 13.27 83.30” 286° 1907/2002
Distance: 116 Light Years
Spectral Classification: “A” is F5, “B” is F9, “D” is G1
Status: AB are physically related per SHY
If you go back to our second chart above (also here), you’ll find a line drawn through HIP 51290 and Bu 1074 leads you directly to SMA 75, which stands out conspicuously from the surrounding stellar terrain.
And considering the confined spaces we’ve been restricted to on the last two stars, your first view of this system will be a veritable breath of fresh air:
In fact, after the barren nature of most of the Ursa Majorian spaces I’ve explored over the last few months, SMA 75 is an oasis of stars in a desert of darkness.
I didn’t have any luck at all with trying to ferret “P” out of the glare caused by “A” and “B”, but it’s there, as this photo shows . . . . . . .
. . . . . . . and should have been visible in my six inch f/10, so a return visit has already been put on the agenada.
I included the WDS dates of first observation in the data line above to provide some insight into the history of this group of stars, which has undergone rather extensive observation. The WDS text file on SMA 75 (provided courtesy of Brian Mason of the USNO) shows a total of sixty-six separate observations made by various people from 1874 to 2012.
The first observation of the AB pair was made in 1874 by Baron Ercole Dembowski, who is credited with it on p. 111 of S.W. Burnham’s 1906 General Catalogue of Double Stars Within 121° of the North Pole — it’s shown in the thumbnail at the right under Burnham’s catalogue number, 5537.
In 1907, Ejnar Hartzsprung, better known for his contribution to the life cycle of stars portrayed by the Hartzsprung-Russell Diagram, added measurements for AC and AD, as well as taking notice of the position of the star now designated as “P”. I was able to track down his efforts in this publication, and have included the specific observation below:
Note that his observation is also identified with Burnham’s catalogue number, 5537. Also, the position angle shown for BD (170.4°) is off by 180º (an easy mistake to make in this part of the sky), which was corrected in subsequent publications.
In 1930 these stars were paid a visit by William Marshall Smart, whose initials are now used in the form of SMA to identify this stellar collection. He contributed a photographic measurement of the AB pair, which was published here. I’ve included an excerpt from the page showing that observation below . . . . . . .
. . . . . . which also uses Burnham’s General Catalogue number to identify the star.
And that raises the question of how this system of stars picked up the SMA designation. Even though Dembowski and Hartzsprung contributed measurements prior to Smart’s photographic measures, Burnham’s catalogue number 5537 stuck as their only identification. Apparently a decision was made to finally correct that situation — no clue as to the details of it — but at any rate, we now know them as SMA 75 instead of 5537.
I tracked down the 1958 observation shown for the AD pair to the Second Catalogue of the Astronomische Gesellschaft (AGK2), but was unable to shed any light on who performed the measurement of it.
Next time out — if the weather and the seeing will cooperate — we’ll take a tour on the south side of the lovely reddish-orange Tania Australis and see if we can raise our visual acuity to the same level as that of the eagle-eyed S. W. Burnham, double star astronomer extraordinaire.
Until then, Clear Skies! 😎