• Choose a post by category or constellation

  • Learn the Night Sky

  • Search strategies

    Use the Search box below to find doubles by popular name, RA, or telescope size. For example, a search on "15h" will find all doubles we've reported on that have an RA of 15 hours. A search for "60mm" will find all doubles where we used that size telescope.

Roaming through the Ram, Part Two: 10, 14, 30, and 33 Arietis

. . . . . . . . and A Short Study in Proper Motion

Time now to return once again to the land of the Ram, otherwise known as Aries, and continue our explorations in an eastward direction.   If you missed part one, you can find it here.

Before we get started, it’s been pointed out that I may have been too hard in part one on Aquila, Pegasus, and Pisces with regard to a lack of double star attractions.  Peter Morris has mentioned three stars in Aquila worth taking a look at (5, 15, and 57 Aquilae), one in Pegasus (Enif, aka Epsilon {ε} Pegasi), and four in Pisces (35, 65, Psi-1 {ψ-1}, and Zeta {ζ} Piscium).  I’ve looked at 57 Aql (here) and would agree with Peter – apparently it got lost in my double star cluttered cranium.   Enif I’m familiar with as marking Pegasus’ nose, but I was totally unaware of its double star status.  In fact, it’s actually a very interesting variable which is classed as a “flare” star.  Jim Kaler has some interesting information on it here.  As for Pisces, I’ll have to do some exploring – I need to spend more time in that constellation anyway.

At any rate, many thanks to Peter for his comments, which just point out how incredibly involved and numerous double (and multiple) stars are.  No matter how many years you spend on them, there are always more out there waiting for your eyes to take them in.   After all, there are over 125,000 double and multiple stars cataloged in the WDS (Washington Double Star Catalog), and when you allow for those too faint or too close for the average telescope, there are still plenty left to keep a person busy for years.  If only 25% of that total is within reach of the average backyard telescope (only a guess), that still leaves over 31,000 pairs to track down . . . . . . . and the (ahem) Ram-ifications of that are mind boggling.

On to Aries now.  This is the wide view of where we’re going:

You have to look carefully to locate Aries since it’s in an inconspicuous region of the sky, but once you become familiar with it, it stands out well.   Fortunately it’s not far from the Pleiades (about 25 degrees), which helps to pin it down.  (Stellarium screen image with labels added, click to enlarge).

Stellarium screen image with labels added, click to enlarge.

And this is a close up of the area with all eight of the stars on the two Aries tour labeled in blue:

We’re going to take a look at eight double or multiple stars over the course of two tours, all of which are labeled in blue in the chart above.  Quite a few of the eight are great targets for 60mm refractors, which I’ll mention along the way.  (Stellarium screen image with labels added, click for a larger view).

Stellarium screen image with labels added, click for a larger view.

We’ll pick up with 14 Arietis, which is conveniently located two and half degrees north of second magnitude Alpha (α) Arietis, aka Hamal.  You’ll find it conveniently parked about 25 arc minutes east of sixth magnitude 16 Arietis.

14 Arietis  (H VI 69)  (S 406)  (STTA 23)            HIP: 10053   SAO: 75171
RA: 02h 09.4m   Dec: +25° 56’
Magnitudes   AB: 4.99, 8.01    AC: 4.99, 7.97
Separations  AB: 93.30”          AC: 104.50”
Position Angles  AB: 34°  (WDS 2011)   AC: 279° (WDS 2012)
Distance: 320 Light Years
Spectral Classifications:  “A” is F2, “B” is K0, “C” is F2

And I admit to being swept off my feet immediately on first sight:

A nice wide pair, not the least challenging, that offers striking color and an eye-pleasing configuration.   (East & west reversed to match the refractor view, click on the sketch to improve the view).

A nice wide pair, not the least challenging, that offers striking color and an eye-pleasing configuration. (East & west reversed to match the refractor view, click on the sketch to improve the view).

My first view of this endearing triple star was in my six inch f/10 refractor, which yielded a yellow-white primary leaning toward gold.   I was back the following night with my 80mm f/15 Mizar refractor and struck true gold that time using a 26mm Celestron Plössl (46x).  I didn’t get a 60mm view of this system, but it should do quite well in a 60mm refractor.

Sir William Herschel was here on a winter evening in 1781 (December 27th) and surprisingly tied only one of the two nearby stars (now designated “C”) to the primary.

Wm. Herschel on 14 Ari

His position angle translates to 278° 48’ in our usage, which matches the 2012 measurement for “C”, but his separation of 89.5” is closer to the current WDS data for “B”, leaving me wondering if he didn’t measure it instead of the other star.  So I began to follow a trail of bread crumbs which led first to Sir James South.

James South on 14 AriSir South paid a visit to 14 Arietis twice in December of 1823 and, as you can see by clicking on the thumbnail image at the left, he also measured the star now identified as “C” while ignoring what is now identified as “B”  —–  BUT  —–  he did remark on the questionable separation provided by William Herschel.  Instead of casting a curious eye toward “B”, he attributed the questionable measurement to a problem with the micrometer device Herschel employed.

Not surprisingly, it took the discerning eye of S.W. Burnham to recognize what actually had happened, which he summed up quickly in his 1906 account of 14 Arietis, although where he referred to “angle”, I believe he meant separation since the angle is correct.

Burnham on 14 Ari

He also mentions the proper motion of both the primary and secondary, which we’ll return to shortly.

For now, though, let’s move on and over to 10 Arietis, which lies slightly more than a degree east of our current location (here’s the second chart again).

10 Arietis  (Σ 208)               HIP: 9621   SAO: 75114
RA: 02h 03.7m   Dec: +25° 56’
Magnitudes    AB: 5.82, 7.87   AB,C: 5.67, 13.50
Separations   AB: 1.48”            AB,C: 95.30”
Position Angles  AB: 346° (WDS 2014)    AB,C: 150° (WDS 2001)
Distance: 173 Light Years
Spectral Classification: “A” is F8, “B” is F9
Notes: AB is gravitationally linked — the orbit can be seen here.

This is the first double or multiple star on our two part tour of Aries that didn’t catch Sir William Herschel’s attention, and one quick look explains why:

This one is not for the faint of heart, and it’s certainly not material for a 60mm refractor!  The primary is an obscuringly bold white, while the secondary is barely visible in this view through a six inch refractor at 152x.  The 304x view in the inset at the right just about doubles the apparent distance between the two stars, but they still appear to be locked in a tight embrace.   (East & west reversed, click on the sketch to get a closer look).

This one is not for the faint of heart, and it’s certainly not material for a 60mm refractor! The primary is an obscuringly bold white, while the secondary is barely visible in this view through a six inch refractor at 152x. The 304x view in the inset at the right just about doubles the apparent distance between the two stars, but they still appear to be locked in a tight embrace. (East & west reversed, click on the sketch to get a closer look).

With two magnitudes of difference between the primary and a less than spacious separation of 1.47”, 10 Arietis requires aperture, good seeing, and a healthy dose of patience.  If you look closely, you’ll see 13.5 magnitude “C” lurking dimly at the southeast edge of the primary’s glow, which is no simple star to uncover either, given the ten magnitudes of difference between it and the 5.82 magnitude primary.  Clinging to the eastern corner of the view is 7.14 magnitude SAO 75122 at a distance of 9.5 arc minutes from 10 Arietis.

Lewis on 10 ArietisThe distance between the primary and secondary is slowly increasing at about .015 arc seconds per year.  With a long list of observations of the pair having been made over the past one-hundred ninety plus years (223 from 1821 to 2012), the orbital period of 325 years is pretty well pinned down (it has a grade of three in the WDS, with one being the most definitive and nine being the least definitive).  A list of the early observational data for the AB pair of 10 Arietis, along with an early attempt at plotting an orbit, can be seen by clicking on the thumbnail image at the right.

And once again, mention is made of proper motion in that excerpt from Lewis’s book, and again, we’ll get to that shortly.

Now we’ll take a long leap in an eastward direction in search of a much wider pair, 30 Arietis.   Here’s our second chart again, which you’re going to need.  Starting from our current location at 10 Arietis, hop back to 14 Arietis and continue east to sixth magnitude 16 Arietis and 5.8 magnitude 20 Arietis.  Then slide south about three quarters of a degree to 5.6 magnitude 21 Arietis.  From there we’ll traverse five degrees due east with a slight southern touch to reach our goal.  As you begin nudging your scope eastward, you should see the 6.5 magnitude glow of 30 Arietis come into view.

30 Arietis  (H V 49)  (SHJ 32)  (STTA 29)          HIP: 12189   SAO: 75471
RA: 02h 37.0m   Dec: +23° 49’
Identifier          Magnitudes        Separation    Position Angle      WDS
STFA 5         AB: 6.50,  7.02            38.00”                 275°               2012
RAO 8   Ba,Bb: 7.02, 11.00              0.50”                 286°               2013
Distance: 129 Light Years
Spectral Classifications: “A” is F5, “B” is F7

We’re back in more expansive territory now, which means this is another pair of stars that does well in a 60mm refractor.

Less demanding of our star splitting talent, the hushed yellow glow of this pair of stars is a comfort to our ocular apparatus.  The primary, being a half magnitude brighter than the secondary, is slightly richer in color.  (East & west reversed once more, click on the sketch for a more colorful view).

Less demanding of our star splitting talent, the hushed yellow glow of this pair of stars is a comfort to our ocular apparatus. The primary, being a half magnitude brighter than the secondary, is slightly richer in color. (East & west reversed once more, click on the sketch for a more colorful view).

This is a system that has more names than it does components, and appears to have been a stopping point for all of the double star greats.

Wm. Herschel on 30 Arieta

William Herschel was here on October 15th, 1781; James South and John Herschel on December 6th and 8th of 1821; and F.G.W. Struve and his son, Otto, came along shortly afterwards.

S. W. Burnham made his way to it in 1904 and came to the conclusion the primary and secondary were fixed in relation to each other, which would make them either an optical pair or a physical pair linked by proper motion.

Burnham on 30 Ari

The Washington Double Star Catalog (WDS), on the other hand, refers to an estimated orbital period of 34,000 years.  What we know for certain, as Burnham indicates, is the two stars are moving eastward at an almost identical rate.  Again, we’ll return to that subject shortly.

The most recent addition to 30 Arietis, RAO 8, came in 2012 as part of a project using a “visible-light laser-adaptive-optics instrument” on a sixty inch scope located on Mt. Palomar.  More on that project can be found here, including a photo at the top of page five of a pair of stars separated by 0.14”.

And finally, on to the final star in out Arietal tour, which is located 2.5 degrees northeast of our current location.  As you move your scope in that direction, you’ll see 33 Arietis lying just short of a degree south and west of 5.3 magnitude 35 Arietis.  (Here’s our previous chart once more).

33 Arietis  (H IV 5)  (SHJ 33)  (Σ 289)       HIP:12489   SAO: 75510
RA: 02h 40.7m   Dec: 27° 04’
Magnitudes: 5.30, 9.56
Separation:  29”
Position Angle: 3°  (WDS 2012)
Distance: 234 Light Years
Spectral Classification: A3, A2

I tracked this one down with my 80mm f/15 Mizar refractor, not really expecting to catch the secondary since it’s 4.26 magnitudes fainter than the primary.  Surprisingly I succeeded in prying loose the 9.56 magnitudes of faint light, although it was mainly an averted vision affair:

Needless to say, this one is not 60mm refractor material.  It’s also a rather lonely field, with not much of anything to draw your attention aside from 8.25 magnitude SAO 75522 in the southeast corner of the field.  But in an odd way, there’s something compelling about the sheer sparse quality of the view with the 5.3 magnitudes of white light at the center.  (East & west reversed once more, click on the sketch for a much better view).

Needless to say, this one is not 60mm refractor material. It’s also a rather lonely field, with not much of anything to draw your attention aside from 8.25 magnitude SAO 75522 in the southeast corner of the field. But in an odd way, there’s something compelling about the sheer sparse quality of the view with the 5.3 magnitudes of white light at the center. (East & west reversed once more, click on the sketch for a much better view).

Sir William Herschel was here on September 27th, 1779, and came up with measurements that are close to those of the 2012 figures shown above from the WDS.  His 87° 14’ should include the phrase “north following,” which would equate to 2° 46’ in today’s double star language.

Wm. Herschel on 33 Arietis

As for his statement about 33 Ari being “the first in the head of the fly” – a phrase I can’t say I’ve ever heard uttered in connection with a double star – it happens to be a reference to a now defunct constellation that at one time hovered over the back of the Arietal Ram.  It went by the name of Musca Borealis, which translates as The Northern Fly, and consisted of 33, 35, 39, and 41 Arietis.  You can find a discussion by Ian Ridpath here, and there’s a detailed 1822 plate showing the fly hovering over the Ram’s rear quarters here.

Click to enlarge.

Click to enlarge.

Speaking of 1822, James South and John Herschel recorded a visit to 33 Arietis on January 28th and February 1st of that year.  Their measurements differ very little from William Herschel’s, but what caught my eye were these comments: “Double; considerably unequal; large white, small blue.  The small star does not bear a good illumination.”  Keeping in mind they were using a 96.5 mm f/15 refractor, they couldn’t have been more correct about the faint secondary, and I’m amazed they were able to measure its separation – obviously it wasn’t easy, as the remark about it not bearing “a good illumination” indicates.

Now, on to a different aspect of all four of these stars which caught my attention as I looked up the details on them.

** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **

A Short Study in Proper Motion

First, to set the stage so we’re all moving together in the same direction, proper motion at its most basic is the apparent motion of a star across the celestial grid marked out by right ascension and declination, and is measured in arc seconds per year.   But it’s also affected by the star’s distance and intrinsic speed, as well as the degree to which the star is moving directly toward us or away from us.  A more detailed — but very basic, informative, and condensed — discussion of proper motion can be found here in this outline of an Ohio State University lecture.  Another useful link is this 1999 discussion by Phil Plait of Bad Astronomer fame (he’s actually a pretty darn good astronomer).

Now – what captured my attention as I excavated information from my stellar vault about the four stars in this tour was the similarities in their rates and directions of motion.

First, I’ll list the proper motions that are known for each star in the tour:

14 Ari —  “A”: +071  -041   “B”: +065  -034    “C”: +074  -037
10 Ari —  “A”: +134 +010   “B”: +134 +010  (identical because gravitationally linked)
30 Ari —  “A”: +135  -015   “B”: +143  -014
33 Ari —  “A”: +065  -026   “B”: +065  -029

So – what do those numbers mean?  The first three of each six digit series is movement in right ascension (east or west), and the second group of three numbers is movement in declination (north and south).  A plus sign indicates eastward movement in RA and northward movement in declination, while a minus sign means westward motion in RA and southward motion in declination.

As for the numbers themselves, think of each three digit series of numbers as having a decimal in front of it.   In other words, in the case of 14 Ari, when your imagination supplies the decimal, this is what you would see: +.071 and  -.041  —-  and to complete the picture, we’ll add the symbol for arc seconds, which results in this appearance: +.071” and -.041”.

What those two numbers mean is the primary (“A”) of 14 Ari is moving eastward at a rate of .071” per year and southward at the rate of .041” per year.  The next set of numbers tells us the secondary (“B) is moving eastward at a rate of .065″ and southward at the rate of .034” per year, and “C” is moving .074″ north and .037″ south per year.

As you can see by the plus signs in the RA columns, all of these stars are moving east, with 10 and 30 Arietis moving in that direction twice as fast as 14 and 33 Arietis.  Their rates of movement in declination are similar, with the exception that both components of 10 Arietis are moving slightly north, while the others are all moving toward the south.

Now, let’s put those figures above into pictorial form.  To save space and avoid clutter, I’ll combine the individual Simbad charts into two groups:

Simbad 14 and 10 Aries

Click on either of the charts to enlarge.

Click on either of the charts to enlarge.

Now, let’s take our proper motion table above and add the distance to each star:

14 Ari —  “A”: +071  -041   “B”: +065  -034    “C”: +074  -037    320 Light Years
10 Ari —  “A”: +134 +010   “B”: +134 +010                                    173 Light Years
30 Ari —  “A”: +135  -015   “B”: +143  -014                                    129 Light Years
33 Ari —  “A”: +065  -026   “B”: +065  -029                                    234 Light Years

Not surprisingly, the two fastest moving systems of the group, 10 Arietis and 30 Arietis, are the closest of the bunch.   Relative to 10 and 30 Arietis, the most distant of the group, 14 Arietis, is actually moving along at a rather respectable rate.   If it was half as far, it’s proper motion figures would be very similar to 10 and 30 Arietis.

What those figures don’t tell us is how fast the stars are moving towards us or away from us (their radial direction).  When you have that information, as the previously mentioned Ohio State University lecture shows in graphic form (there’s an excellent diagram labeled “True Space Motions” about three-fourths of the way down showing all of this), you have a complete picture of the actual motion of the star.

A couple of other items that show up on the charts above:

The large galaxy in the center of the plot for 10 Arietis is MCG+04-05-047, with a magnitude of 14.7 (in blue light).  More interesting still is the reference to a planet on the chart for 30 Arietis, which looks like this when we zoom in to a 5 arc minute view (the earlier four charts are all 10 arc minute views):

Click on the chart for a more planet friendly view.

Click on the chart for a more planet friendly view.

The object shown on that chart is thought to be either a very large planet or a brown dwarf with an orbital period of 335.1 days around 30 Arietis B.  Here’s a chart with all of the pertinent data, and here’s a short seven page paper which discusses both the planet and the host star.

For those interested, here are the links to the Simbad charts shown above:

14 Arietis
10 Arietis
30 Arietis
33 Arietis
30 Arietis with planet

Before I forget about it, here ‘s the link to the William Herschel, John Herschel, and James South excerpts from the Royal Society’s Philosophical Transactions.  Find the volume number mentioned at the bottom of the excerpt, click on it, and you’ll see a table of contents for all the articles in that volume.  Clicking on a title will provide you with a .pdf version of the article — lots of interesting titles in those old issues!  And this link will get you to volume two of Burnham’s 1906 double star catalog (volume one is here).

And that should be enough to keep you busy for a while on those cloudy nights when the stars refuse to show themselves. 😎

Next stop will take us south to stellar realms I’ve never explored before, so stay tuned!

Advertisements

3 Responses

  1. Read and enjoyed the Ram part 1 and the very next clear night went out and split your targets myself with my 5″achro…
    im looking forward to the next clear spell so I can attempt part 2..
    .awesome work keep it up guys best newsletter I ever subscribed to.

  2. Hi John!
    Another exquisitely detailed trip through the Celestial treasure trove. As always, great sketches, informative re-directs and well documented research. When do you sleep, good buddy?

    Cheers, Chris.

    • Thanks to both Darren and Chris for the comments.

      As for sleep, that’s what cloudy nights are for. Finally getting some now, so it’s time to catch up!

      John

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: