NBWS (Note before we start): It’s getting a bit late in the year for this part of the sky, so if Canis Minor is lost in the evening’s glare where you are, park this piece for a few months until it returns to a more favorable position. Time got away from me on this one).
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Been feelin’ a bit bleary-eyed, lately? Too many late nights under the stars followed by early morning wake up calls from a very impolite and shrill alarm? Well if that’s the case, you might just as well focus those bleary eyes on a star that’s been named in your honor.
Gomeisa, the Beta (β) star of Canis Minor, earned its name from an early Arabic astronomer who apparently kept the same schedule. It seems Gomeisa is an Arabic phrase meaning “the little bleary-eyed one.”
And it has enough companions that just trying to track all of ‘em down will leave you more than a little bleary-eyed.
Meanwhile, over in the southeast corner of Canis Minor you’ll find another multiple star with a few less companions, but certainly no less challenging. And hovering near enough to be irresistible is an S.W. Burnham discovery, which of course includes one of his signature visual challenges guaranteed to give your ocular apparatus a whopper of a workout.
First, let’s pin down the location of Gomeisa, which is pure simplicity itself:
Beta Canis Minoris (Gomeisa) (3 CMi) HIP: 36188 SAO: 115456
RA: 07h 27.2m Dec: +08° 17’
|Discov#||Comp||First||Last||PA||Sep||Mag 1||Mag 2|
Distance: 170 Light Years
Spectral Classifications: A is B8
Hiding somewhere in that glare is the secondary (“B”), which was beyond my visible grasp. For some reason the most concentrated part of the glare was right in the area where “B” should have been. Also out of visual reach was the 13.4 magnitude “H” component, which should have been parked tightly against “F”. And of course, the 19.8 magnitude “I” and the 17.8 magnitude “J” companions were so far out of visual reach they might just as well have been located in an adjacent universe.
Steve Smith was able to capture both the elusive “B” and the faint “H” components in the photograph below, which also gives you some idea of why “B” is so difficult to catch visually. In fact, there’s another star in his photo located midway between “B” and “D” which also escaped my eyes, that appears to be in the neighborhood of 14th magnitude. Never under estimate the ability of a good photograph to penetrate the glare that plays havoc with the eyes!
You can see Burnham’s data on the AC, AD, and AE components on the adjacent page from his catalog, from which he derived a proper motion of -058 -032 (.058” per year west and .032” per year south).
Those numbers have been revised slightly in the current WDS listing to -052 -038, which isn’t much of a change considering the differences in technology between 1908 and the 2008 WDS readings.
Here’s a look at the Simbad plot of the primary’s proper motion:
When the primary’s 170 light year distance is taken into account, that seemingly minor amount of movement is actually rather significant. The effect of that motion can be seen by comparing Burnham’s measures with those from the WDS listed at the top of this section.
The WDS shows the first date of observation for the AB pair as 1831, which led me to suspect it was an F.G.W. Struve discovery. After rummaging around through my accumulation of sources, I discovered the 1831 measures (80 degrees and 35”) were from Admiral William H. Smyth’s entry on Beta (β) CMi in his Bedford Catalog (p. 203 of this edition, which is part of his A Cycle of Celestial Objects). Smyth refers to some measures of other stars in the field by Piazzi, none of which I’ve been able to track down.
14 CMi (SHJ 87) (AB is H VI 84) HIP: 38962 SAO: 116182
RA: 07h 58.3m Dec: +02° 13’
. Magnitudes Separation Position Angle WDS
AB: 5.41, 9.36 100.00” 84° 2011
AC: 5.41, 9.89 136.90” 149° 2011
AD: 5.41, 11.00 114.20” 281° 1999
BC: 9.36, 9.89 127.90” 193° 2004
Distance: 265 Light Years
Spectral Classifications: “A” is K0, “B” is A0, “C” is K
Notes: Notable PM of primary (-162 +099)
Despite being assigned a James South-John Herschel prefix (SHJ) by the WDS, it was William Herschel who first discovered 14 CMi as a triple star on February 9th, 1782. He measured the AB separation at 65.47” with a PA that translates into 63° 26’ under the present system of measuring position angles. He apparently didn’t make any attempt to measure “C”, instead describing it as forming an angle with “A” and “B” and placed it in the south following quadrant (source for excerpt below):
Forty years later, almost to the day, the duo of James South and John Herschel turned their 3.75” refractor on 14 CMi and, much to their surprise, discovered a very noticeable change in separation and position angle of the AB pair (source for excerpt below, scroll down to the last title).
They took seven measurements, which yielded an average separation of 76.021” and a position angle of 65° 42’. They also made a single measure of AC at 112.168” and 152° 50’. But it was the change in AB that caught their attention, leading one of them to describe the increase in separation as “very remarkable.”
As we now know, the primary of 14 CMi is the primary culprit for the changes noticed by John Herschel and James South. Both Simbad and the WDS measure its motion at -162 +099 (.162”/year west, .099”/year north), which is even more remarkable than that of the Gomeisa primary since 14 CMi A is another ninety-five light years further away (265 LY). In fact, it’s not only further away, but the rate of motion is three times faster. You can get some idea of the difference in rate of motion by comparing the Simbad plot of 14 CMi shown below with that of Gomeisa:
Now on to Bu 23, located a very short 1° 21’ to the northeast of 14 CMi. We’ll use our previous chart, but we’ll add distance measurements between the stars to give you a senses of scale:
Bu 23 No HIP SAO: 116264
RA: 08h 02.5m Dec: +03° 05’
. Magnitudes Separation Position Angle WDS
AB: 8.27, 12.10 2.70” 181° 1936
AC: 8.27, 11.27 103.50” 309° 2000
CD: 11.27, 12.60 11.40” 235° 2000
Spectral Classifications: “A” is K0
Notes: Notable PM of “C” (+105 +069)
The CD pair is parked northwest of the primary, and is labeled in the inset in case the two stars escape your attention. Even in this tight seventeen arc minute field of view, HIP 39302’s K2 orange glow managed to sneak into the southwest corner of the field.
Bu 23 strikes me as a strange little discovery for a couple of reasons. First, the dim magnitudes of the CD pair produce a tenuous appearance in the eyepiece, which gives the two stars a haunting quality. And second, I’ve also noticed what seems to be a reluctance to fully acknowledge them at the time of discovery.
S. W. Burnham discovered all four of the components on February 2nd, 1872, with his six inch f/15 Clark refractor, but only provided an estimate of 180 degrees and 3 arc seconds for the position angle and separation of the AB pair (source for the image below):
Without means of obtaining a precise measure at the time, he referred the AB pair to Baron Dembowski, who measured them at 177.0 degrees and 2.81” in 1875. Burnham later measured them at 181.9 degrees and 2.62” in 1891, and R.G. Aitken came up with 178.0 degrees and 2.48” in 1898.
That gets us back to the hauntingly faint CD pair, which Burnham referred to almost parenthetically as “a very faint pair in the n p quadrant [n p is north preceding], about 100” from the primary.” The WDS shows 1872 as the date of first measurement for AC, with a position angle of 315 degrees and a separation of 100”. Burnham didn’t measure that pair in 1872, as far as I can determine, other than to estimate their distance from the primary. Nor does he provide any data on the CD pair in his 1900 General Catalogue of 1290 Double Stars Discovered from 1871 to 1899 (p. 94), which is the volume that lists all of the discoveries associated with his Bu (or β) prefix, and apart from alluding to their being visible in the north preceding quadrant, he also ignores the pair in the second volume of his 1906 General Catalogue of Double Stars Within 121° of the North Pole (p. 508).
But “C” is worth some attention in its own right since it appears to be passing by to the northeast at a rather determined pace. The WDS shows it has a proper motion of +105 +069 (.105”/year east and .069”/year north), while Simbad is slightly different at +095 +069. I came up empty handed in a search for the distance of Bu 23 — and even if it was known, there’s no assurance it would apply to “C” — so there’s really no way of putting that motion into perspective. At any rate, here’s Simbad’s plot of “C’s” proper motion relative to the AB pair:
So there you go – three stars picked pretty much at random (thanks again to Chris Thuemen for calling may attention to Gomeisa over a year ago), and all of them showing varying degrees of restlessness. I never cease to be amazed at what I find when I start researching multiple stars. The starry heavens are filled with enough beauty and surprise to keep a person busy for several life times.
Next time – off to comb the knots out of Bernice’s hair in Coma Bernices.
Clear skies until then! 😎