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The Weird and Wonderful World of 8 Andromedae: BU 717, ES 2725, and ARY 3

On one of those crisp September nights when I was lingering in Lacerta over delicately separated double stars and diminutively defined open clusters, I happened to look away from the eyepiece just long enough to catch sight of an arc of three faint stars lined up on the Andromeda side of Lacerta (as opposed to the Cygnus side — see chart below).  Puzzled because I had never noticed them before, I flipped open my dog-eared copy of Sky and Telescope’s Pocket Atlas to Chart 72 and identified the three stars as Iota (ι), Kappa (κ), and Lambda (λ) Andromedae. I noticed the three stars were devoid of double star designations (although Kappa is most definitely a multiple star that goes by the designation HJ 1898), but my wandering eyes were quickly drawn a few degrees north to another concentration of stars curving towards Lacerta, which were labeled as 11, 8, 7, and 3 Andromedae. And that subtle little international double star symbol — a line drawn through the dot of a star on a star chart – that short line that makes the heart of every double star enthusiast skip a few beats and then pulsate as wildly as Sirius when its five degrees above the horizon . . . well, let’s just say that horizontal splash of line split more than a few dots of stars.

In other words, a veritable double star feast before my very eyes.

But before we dine on double stars, first we need to take a careful look at this area, because it’s very easy to mistake the Iota (ι), Kappa (κ), and Lambda (λ) trio for our destination, which instead is the threesome of 11, 8, and 7 Andromedae.

Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

When you first cast skyward eyes on the general area at the center of this chart, Iota (ι), Kappa (κ), and Lambda (λ) Andromedae catch your gaze first because they’re brighter than 11, 8, and 7 Andromedae. The first three stars have magnitudes of 3.82, 4.14, and 4.29, respectively, whereas the last three are notably fainter at magnitudes of 5.44, 4.86, and 4.53, again, respectively. But if you follow the arc formed by Iota (ι), Kappa (κ), and Lambda (λ) as it curves toward the southern edge of Cepheus, you’ll find it takes you right over the top of 11, 8, 7, and 3 Andromedae.

Again, you have to be careful here because your eyes are likely to miss the first of that group, 5.44 magnitude 11 Andromedae, and instead will be drawn to 8, 7, and 3 Andromedae, that last one’s 4.66 magnitude being distinctively brighter than 11 Andromedae. But once you point a finder at 8 Andromedae, the middle star of the trio we’re concentrating on, you’ll find 11 and 7 Andromedae become distinct — as the chart below shows:

Stellarium screen image with labels added, click to enlarge.

Stellarium screen image with labels added, click to enlarge.

We’re going to take a look at a total of six double and/or multiple stars in this area, so to keep the length of this thing from getting out of control, I’ll divide our excursion into two parts. This first part will look at 8 And, ES 2725, and ARY 3.

8 Andromedae also goes by the double star designation BU 717, and that’s where we’re going to start – and also where we’re going to find a mysterious surprise.

BU 717  (8 Andromedae)  HIP: 115022  SAO: 52871
RA: 23h 17.7m   Dec: +49° 01’

Identifier Magnitudes Separation PA WDS
BU 717 AB: 5.01, 13.00 7.8” 160° 2015
BU 717 AC: 5.01, 10.83 217.3” 131° 2008
FOX 273 AD: 5.01, 12.46 58.6” 233° 2007
WAL 147 AE: 5.01, 12.34 97.9” 107° 1903
KUI 116 AF: 5.01, 16.00 14.6″ 179° 2015
KUI 116 BF: 13.00, 16.00 7.6” 200° 2015

Distance: 563 LY (Simbad)
Spectral Class: A is M2

Once you get past the irresistible orange glow of the primary, the companions to look for are C, D, and E. The secondary, B, is irretrievably buried in primarial glow (thanks to the eight magnitudes of difference between A and B at a distance of 7.8”), and with the F component hampered by a magnitude of 16, it’s well out of reach. (East and west reversed in this sketch to match the SCT view, click for the larger version).

Once you get past the irresistible orange glow of the primary, the companions to look for are C, D, and E. The secondary, B, is irretrievably buried in primarial glow (thanks to the eight magnitudes of difference between A and B at a distance of 7.8”), and with the F component hampered by a magnitude of 16, it’s well out of reach. (East and west reversed in this sketch to match the SCT view, click for the larger version).

I’ve looked at 8 And/BU 717 with both a five inch refractor and the 9.25 inch SCT used for the sketch, and in each case I had little problem digging C, D, and E out of the rich orange glow of the primary, although I had to call on averted vision to pry D and E out of the sky in the five inch refractor. BUT – despite this apparent cooperative beginning – I was confronted with a perplexing problem when I first peered into an eyepiece and started identifying components.

Where in the world is WAL 147???

On the night I first glued my observing eye to 8 And/BU 717, the AE pair (WAL 147) was listed in the WDS with a distance of 57.1” at a position angle of 89 degrees. For the sake of relative spatial comparison, I had the AD pair (FOX 273) which the WDS showed parked at a distance of 58.6” from the primary. So with both the D and E components having (supposedly) similar separations, and E (supposedly) parked almost right at 90 degrees, I knew exactly where to look – and there wasn’t anything there. That spot was simply empty, unoccupied, vacant – devoid of stellar light, in other words. So where in the astronomical world was WAL 147?

I had also noticed the magnitudes of D and E were very similar, 12.46 for D and 12.34 for E, so I began scanning for a star similar in magnitude to D – and I found one, parked a bit further south of the 90 degree position and at almost double the distance listed in the WDS. But that distance caused skeptical alarm bells to shatter the peace and quiet of the night, so after carefully sketching the position of that star in relation to all the others, I retired to a drier, warmer, and more comfortable spot in front of a computer, pulled up an Aladin image of BU 717 on a computer screen, and went to work.

Aladin allowed me to do two things – check the magnitude of the star I flagged as a possible candidate for the E component, and measure its distance and position angle.

To avoid confusion, I’ve flipped the Aladin image to match my sketch of BU 717 above, so west is at the left and east at the right. Aladin image with data and labels added, click to enlarge.

I’ve labeled the C, D, and E components in the image above, and below the image I’ve added the WDS data which was current at the time I sketched BU 717. Notice the measures for AE are shown as 57.1” and 89 degrees – that spot is labeled in the image with an “X”. You can see a star near that location which is shown with a magnitude of 17 in the URAT1 catalog, which is far too dim to be a candidate for the 12.34 magnitude WDS companion, and of course was well out of the reach of both of my telescopes.

Also shown to the right of the WDS data are the measures I plotted using 2015.0 GAIA coordinates, which in the case of the C and D components differ somewhat from the older WDS data. After I sent my findings to Bill Hartkopf at the USNO/WDS, he established a separation of 97.9” and a PA of 107 degrees for the AE pair, which is both wider and a bit more southerly than what I came up with using GAIA data. However, that data is based on a 1903 measure (probably from a photographic plate), which is now the only observation and measure listed in the WDS for WAL 147. Prior to sending my findings to the WDS, there were observations dated 1944 and 1998, which can be seen in the WDS data beneath the Aladin image above, so it appears there was some kind of error associated with that particular WDS data.

18-5-inch-clark-refractor-at-dearborn-observatory

Click to enlarge.

In case you’re wondering about how that difficult B component we couldn’t see was pried out of the primarial glare, S.W. Burnham managed it in 1887 with the 18.5 inch Clark refractor at Dearborn Observatory (shown at right), which at the time was attached to the University of Chicago. Philip Fox added the C component in 1915, also while using that same refractor.

Now we’ll leave the weird world of 8 And/BU 717 and move on to our last two stars, which agreeably can be seen in the same field of view. This isn’t going to be a difficult move since all we’re going to do is nudge 8 And over to the west corner of our field of view until the similarly-hued 11 And appears in the southern corner of the view. That will put ES 2725 close the center of your field of view and ARY 3 will appear in the southeast corner of the eyepiece, just a bit more than 10’ northeast of 11 Andromedae.

ES 2725     HIP: 115128   SAO: 52899
RA: 23h 19.1m   Dec: +48° 55’
Magnitudes   Aa, Ab: 7.35, 11.20    AB: 7.27, 8.62
Separations   Aa, Ab: 0.5”              AB: 54.1”
Position Angles:  Aa, Ab: 170° (WDS 1991)   AB: 235° (WDS 2013)
Distance  A: 417 LY (GAIA)    B: 1173 LY (GAIA)
Spectral Classes:  A is A2, B is G5
Note: Aa, Ab is HDS 3321, AB is ES 2725

ARY 3     No HIP Number    SAO: 52929
RA: 23h 20.7m   Dec: +48° 48’
Magnitudes: 8.96, 9.47
Separation:  118.1”
Position Angle: 210°  (WDS 2010)
Distance  A:  232 LY (GAIA)    B: 421 LY (GAIA)
Spectral Classes:  A is G5, B is F8

ES 2725 is the pair of stars at the very center of this view, tilted at about a forty-five degree angle (and identified in the box at the right). ARY 3 is the fainter and wider pair at the southeast edge of the view (18’ southeast of ES 2725 and on a line with BU 717 and ES 2725), tilted more noticeably to the north than the ES 2725 pair. (East and west reversed to match the refractor view, click on the sketch to bring it to life).

ES 2725 is the pair of stars at the very center of this view, tilted at about a forty-five degree angle (and identified in the box at the right). ARY 3 is the fainter and wider pair at the southeast edge of the view (18’ southeast of ES 2725 and on a line with BU 717 and ES 2725), tilted more noticeably to the north than the ES 2725 pair. (East and west reversed to match the refractor view, click on the sketch to bring it to life).

Now I know these aren’t the most stunning double stars ever to grace an eyepiece, but since we didn’t have to wander far to find them, we may as well pay them the courtesy of a visit. And with a minimal investment of time, we can even mine a few morsels of information from them. For example, according to GAIA’s data, the A and B components of ES 2725 have 756 light years of distance between them. And the ARY 3 pair are considerably less distant from each other with 189 light years of interstellar space wedged between them. That would make each of them an optical pair, although that doesn’t necessarily apply to the Aa Ab pair of ES 2725, since there’s no data on the distance of that 11.20 magnitude companion sitting half an arc second from the primary.

Not surprisingly, if we look at how they’re moving through interstellar space, we’ll also find there’s no shared motion between each of the pairs.

Aladin images with labels added, PM vectors plotted by Aladin. Click to enlarge.

Aladin images with labels added, PM vectors plotted by Aladin. Click to get a much better view of the directional arrows.

In case the PM numbers at the bottom of the image mystify you, the first of each three digit pair of numbers is the motion in right ascension (east or west) and the second is the motion in declination (north or south). The numbers represent thousandths of an arc second, and the plus sign denotes northerly or easterly motion, whereas the negative sign signifies westerly or southerly motion.

So in the case of ES 2725, the A component is moving east in right ascension at the rate of .078” per year and north in declination at the rate of .008” per year, and the B component is moving east at the rate of .022” per year and north at the rate of .011” per year.  Notice the rate of motion of the primary is greater than that of the secondary, which is not a surprise when you look at the individual distances in the data line above and find the secondary is farther away from us (1173 light years for the secondary, 417 light years for the primary).

The primary of ARY 3 is also moving east and north, but its secondary is moving in the opposite direction at the rate of .042” per year west and .068” per year south. In each case, the arrows correctly indicate the combined direction (right ascension and declination) and the combined rate of motion for each of the components.  Also notice the rate of motion of each of these stars matches well with their distance when compared with the ES 2725 pair.

So there you have it – just enough data about ES 2725 and ARY 3 to tell you more than you knew before you got to this point! You can even pass it on to your friends and neighbors. They’ll either be totally amazed or they won’t speak to you again in public.

Either way, don’t despair, because we’re going to stay in this immediate vicinity for our next trip. We’ll look at three more double and/or multiple stars . . . and who knows what arcane details of stellar motion we’ll uncover next.

Clear Skies! 😎

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