EZ Aquarii

EZ Aquarii

Also known as Luyten 789-6, GCTP 5475.00, LHS 68,

GJ 866, G 156-031

     EZ Aquarii is this star system’s most commonly-used designation, but I personally prefer the name Luyten 789-6. Willem Jacob Luyten (1899-1994) was perhaps responsible for more knowledge being learned about the universe’s faintest (and commonest) stars than anyone else. He was, in fact, the first astronomer to accurately identify the full list of nearby suns, and first to realize that the vast majority of stars in the universe as a whole were very faint indeed. Without his decades long examination of the proper motions of more than a half million (!) stars, this little book would never have been possible.  Like his predecessor in the field, Maximilian Franz Joseph Cornelius Wolf (see posting for Wolf 359), Luyten personally designed and constructed the equipment necessary to carry out his work. In Luyten’s case, he developed an automated photographic plate scanner and measuring machine (christened the “Rapid Scanning Microdensitometer”), constructed to Luyten’s specifications by the Control Data Corporation, in order to study such a stupendous number 

of individual stars.

     Remember, this was still all before the Age of the Computer. As a reminder of such, 

I happen to have before me as I write these words a true astronomical treasure – an original print of Luyten’s 1970 catalog, The Stars of Low Luminosity. It figuratively screams of its origin in a completely different world than ours of today. The manuscript is typed, and the various mathematical symbols not to be found on a manual typewriter (such as that for “greater than or equal to”) were drawn in by hand prior to its printing. And charmingly, on the last page of the catalog, we find the words: “Data for the following stars were overlooked, or did not become available until the main catalogue had been typed.” Then follows the entries for an addition 13 stars, which are of course out of order. (Where is the “Insert Line” function when you need it? In those pre-word processor days, to put those last 13 entries in order would have required the retyping of the entire manuscript!)

     Luyten dedicated nearly his entire career to the study of these least-luminous stars. He would probably have readily seconded Abraham Lincoln’s famous observation, “God must truly love the Common Man; He’s made so many of them.” He was forever concerned that astronomers’ conception of the universe would be radically skewed without taking the ubiquity of such stars into account (shades of today’s interest in “Dark Matter” and “Dark Energy”). Near the end of his life, in a speech before the International Astronomical Union’s Colloquium Number 97, Luyten basically summed up a lifetime of study in the following words:

“We should always remember that of the 6,000 stars that the average human eye can see in the entire sky, probably not more than 30, or one-half of one percent, are less luminous than the Sun; whereas of the 700-odd stars nearer than ten parsecs, at least 96% are less luminous than the Sun.”

     EZ Aquarii was first identified by Luyten as a star of high proper motion and close proximity 

to the Sun. He also discovered its true nature as a multiple star system of three red dwarfs, gravitationally bound in a most interesting manner. EZ Aquarii A and B orbit about a common center of gravity each 823 days, but EZ Aquarii A has a companion of its own (EZ Aquarii C) in a very close proximity. EZ Aquarii A and C circle each other every 8.3 days and are a fine example of a spectrographic binary. They cannot be separated visually. The three stars together have a mass of approximately 34% of the Sun.

     I have to admit that as a die-hard (some say obsessive) star hopper, I find the constellation Aquarius to be just about the most difficult region of the entire sky in which to find anything. (Well, maybe not as bad as Lynx, but at least there’s nothing worth looking for up there, so who cares?) Other than the “Water Jar”, there are no obvious asterisms in Aquarius to draw the eye. I never find the patterns drawn in most star charts to be the least bit convincing. Proof that I’m on to something here is the almost nonexistent agreement the various diagrams have with each other. It’s almost comical how different they can be. What one person sees as the Water Bearer’s knee, another sees as his backside, or even as the water jar itself. Where one chart positions the head, another places a shoulder. To me, the whole thing is just a mess of not-too-bright stars, filling up the space between Capricornus and Pisces.

     But it is what it is, and this is where EZ Aquarii is located. So let’s see what we can accomplish here without too much loss of sanity. We’ll try to make things easier by starting in neighboring Capricornus. Now there’s a constellation which, although it doesn’t look the least bit like a goat, is at least immediately recognizable, its gigantic triangular shape being practically impossible to miss.

Over at the upper left corner of Capricorn’s triangle are the relatively prominent stars Deneb Algedi (magnitude 2.8) and Nashira (magnitude 3.7), or Delta and Gamma Capricorni, respectively. Together these two form a convenient pointer to Iota (magnitude 4.3), and then to Sigma (magnitude 4.8) Aquarii. We’re still nowhere near to our ultimate goal, but from here we can at least see the ballpark. Now from Howard County, we happen to be looking in a singularly unfortunate direction from most viewing sites, since at -15º declination and looking almost due south, we find ourselves squarely in the middle of the Greater Washington, D.C. light dome, where even 4th magnitude stars can be lost in the skyglow. You will need at least binoculars to make out anything dimmer than those stars mentioned here, bravely battering their way through the combined spillage of perhaps two million streetlights. In any case, turning southwest from Sigma Aquarii and sliding past Tau² Aquarii (magnitude 4.0), you will eventually come upon Delta Aquarii (otherwise known as Skat), a 3.25 magnitude star and the third brightest in the whole constellation.

     Here we come to the end of what we can accomplish by naked eye, and perhaps even with the aid of binoculars. I now suggest using your widest field eyepiece, and placing Delta Aquarii at the extreme right edge of your field of view. (Remember, everything is mirror-imaged from here on out).

     Take a good look at the above figure. This is the most difficult star hop we will have attempted thus far, and it deserves the most attention possible. In our mirror-imaged view, proceeding leftward from either Tau 2 or Delta Aquarii along a line of fairly dim stars, we will eventually come upon a neatly-matched pair of parallel optical doubles, slightly less than two full moons’ distance to the southwest and north-northwest of EZ Aquarii. Stay with your wide field eyepiece for a while, since at this point we are still dealing with fairly large swaths of sky.

     (By the way, I simply cannot resist recommending a slight detour a before moving on. Just above the more northerly of the two optical doubles is a most beautiful, although quite faint, sight – the triple star system AB Aquarii. Its deep blue and golden yellow components are more than worth a glance or two along the way.)

     About half way between these two pairs of stars and slightly to the left is the 8.8 magnitude star HD 214687. There is nothing even close to that brightness in the vicinity, so it shouldn’t be too hard to identify.

     In the above figure, we have zoomed into an area about the size of the full moon, with HD 214678 off to the right as the brightest thing around. As you can see, nothing in the immediate neighborhood even approaches this star in apparent magnitude. The 9.9 magnitude HD 214414, off to the other side of our quarry, will help us to focus in on the exact location of EZ Aquarii, below and to the left of the midpoint between these two stars. Every other star in your eyepiece (assuming the Washington light dome allows you to see anything at all) will be dimmer than 10th magnitude. By the way, do not try this with any moon at all in the sky; and hopefully a night of low humidity will cut down on the skyglow for you. Otherwise, proceeding further is quite frankly hopeless.

     One big point in our favor, however, is that despite the extremely low luminosity of the separate components of EZ Aquarius, there are three of them! Individually, their apparent magnitudes are 13.33 for A, 13.27 for B, and 14.03 for C, which equate to a combined magnitude of 12.3. Now that’s doable!

     Now this star chart is basically the same as the last one, with a few less relevant stars omitted for clarity, and the approximate size of the full moon overlaid on the field of view. This figure approximates the area of sky I see using my 10mm Ethos with my 5-inch refractor. Imagining HD 214687 as the tail of an airplane-shaped asterism composed of the brightest stars around, EZ Aquarii is located near the center of the right wing (assuming we are looking up at the plane).

     Now, wasn’t that fun!