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Sagitta Sightings: Epsilon (ε), H N 84, and Zeta (ζ)

After a week of clear afternoons followed just like clockwork by cloudy skies at dusk, I was thrilled to death to get a clear night, even though the moon was almost full.  You can’t be picky when you live on the north Oregon coast, where there are as many clouds as there are seagulls.

The Sagittta arrow aimed high into the northeast — you’ll find all the stars on our tour shown on this chart. North is up in this view, east is to the left. Click on the image for a larger view. (Stellarium screen shot with labels added)

Sagitta has been on my mind for the last month or so (yes, I know,  strange mind — but when it comes to double stars, it goes to its destination like an arrow flies to a target), so I thought I would take a look around tonight, starting at the western end.  The tail of the arrow which outlines this constellation is held down by Alpha (α) and Beta (β), and just south of them are our first two stars, Epsilon and H N 84.  The first was discovered by William Herschel on August 19th, 1780, and the second on August 22nd, 1792.  Both of these can easily be seen in the same field of view in a 60mm scope.

Epsilon (ε) Sagittae  (H VI 26)          HIP: 96516    SAO: 105061
RA: 19h 37.3m   Dec: +16° 28′
Magnitudes   AB: 5.8,   8.4    AC: 5.8, 12.6    AD: 5.8, 9.6
Separation    AB: 87.7″          AC: 101.2″        AD: 162.8″
Position Angles   AB: 82° (WDS 2012)  AC: 278° (WDS 2001)  AD: 348° (WDS 1992)
Distance:  473 Light Years
Spectral Classification:  “A” is G9, “B” is B9, “D” is K0

H N 84         HIP: 96688    SAO: 105104
RA: 19h 39.4m   Dec: +16° 34′
Magnitudes: 6.4, 9.5
Separation:  28.3″
Position Angle: 301°  (WDS 2012)
Distance: 2297 Light Years
Spectral Classification: K4, B3

At 40x in my 60mm, Epsilon’s (ε) primary looked to me to be yellow with a very slight tinge of red and the secondary was white.   I worked hard at trying to get a glimpse of  “C”, but the bright moon, which was about forty degrees away, just made the sky too bright to detect it.  ** Update 11/17/2014:  It appears that the magnitude for the “D” component is incorrect since there is no 9.6 magnitude star at the position given for it.   In fact, there’s not even a star at that location that is anywhere near bright enough to be “D”.   More to come shortly.  **

The colors of H N 84 are very close to those of Epsilon (ε), but the primary is slightly darker and has a bit more red in it.

Epsilon is on the left in this sketch, H N 84 is at the upper right. The "D" component of Epsilon is above and to left of the pale orange primary (near the arrow marking west), and the "C" component is the first (very faint) star immediately to the left of the primary. (East & west are reversed here to match the refractor view, click on the sketch for a better view).

Epsilon is on the left in this sketch, H N 84 is at the upper right. The  “C” component is the first (very faint) star immediately to the left of the primary.  “D” is too faint to be seen in this sketch, and in fact may not even exist.   (East & west are reversed here to match the refractor view, click on the sketch for a better view).

It’s easy to mix these two pairs of stars up on first sight.  You may need to use their position angles to make the distinction when you first come across them, especially if you only see one of them in your eyepiece, which is what happened to me.   In a refractor, you’ll see that Epsilon’s (ε) secondary lies at a position angle of eighty-two degrees, which puts it almost due east of the primary, whereas in the case of H N 84, the secondary lies at 299 degrees, putting it on the opposite side of the primary.  In other words,  these two stars are almost mirror images of each other.  I came across Epsilon (ε) first, thinking it was H N 84, and kept muttering to myself that the secondary was in the wrong place, until the real H N 84 drifted into view in the right side of my eyepiece — and then the light came on!  In the bathroom window opposite my second story observing deck!  Geez, I hate it when that happens.

Zeta (ζ)   (Σ 2585)  (H II 30 — AB-C only)        HIP: 97496    SAO: 105298
RA: 19h 49.0m   Dec: +19° 09′
Magnitudes  AB: 5.6, 6.0    AB-C: 5.0, 9.0    AB-D: 5.0, 11.0
Separation   AB: 0.18″          AB-C: 8.0″          AB-D: 76″
Pos.  Angles  AB:148° (WDS 2007)  AB-C: 311° (WDS 2012)  AB-D:246° (WDS 2005)
Distance: 327 Light Years
Spectral Classification:  “A” is A1, “C” is F5
Status: “A” is a suspected spectroscopic binary; “AB-C” is physically related; “AB-D” is optical

OK, light’s off, so now it’s time to move slightly northeast to Delta (δ) and then a bit north in order to reach Zeta (ζ), which provides a nice contrast with Epsilon (ε) and H N 84.  At 8.0″ apart, you have to look just a bit closer in a 60mm scope to see the AB-C pair.  I could just separate them at 40x, but increasing the magnification to 53x proved to be enough to put some dark sky between them.  I had to bring in the big gun, the 152mm refractor, to make the eleventh magnitude “D” component visible at 87x.  I never did see it in the 60mm, but under a dark sky, with it’s distance of 76″ from the primary, it should be possible to get a glimpse of it.  I increased the magnification on the 152mm scope to 122x and was rewarded with a very nice view of all three components.

This is a recent sketch added three years after the post above was written. I could see a definite yellow tinge in the AB primary, which doesn't at all match it's A1 (white) spectral class. "C" (which is tucked in snugly against the primary at about eleven o'clock) is classified as F5, which should appear yellow-white (if it was bright enough to detect the color). Possibly the AB primary has borrowed a little bit of it's yellow tinge from its fainter companion. East & west are reversed in this sketch to match the refractor view, click on it for a larger and much better view.

This is a recent sketch added three years after the post above was written. I could see a definite yellow tinge in the AB primary, which doesn’t at all match it’s A1 (white) spectral class. “C” (which is tucked in snugly against the primary at about eleven o’clock) is classified as F5, which should appear yellow-white (if it was bright enough to detect the color). Possibly the AB primary has borrowed a little bit of it’s yellow tinge from its fainter companion. East & west are reversed in this sketch to match the refractor view, click on it for a larger and much better view.

If you look at the data for Zeta (ζ) above, you’ll see that “A” and “B” are .18″ of an arc second apart — which means we don’t have a snowball’s chance in a hot oven of separating them.  If you’ve ever wondered what a label such as “AB-C” means, then now you know!  Normally combining the two stars into one by dropping the dash indicates a spectroscopic pair – which these two are not, but they’re pretty darn close.

Time to take a break and put the light screen up.  It looks like the friendly folks next door have decided to leave that minus 15th magnitude bathroom light on all night.

Next stop: Theta!

(WDS info updated 9/8/2013)

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4 Responses

  1. I had a chance to go back and look at all three of the stars described in the post above, probably for the first time since I wrote it. This time I was using my four inch Skylight refractor, and that aggravating bathroom light mentioned in the post was on once again. So up went the light screen — without it on a dark night, I might as well have been sitting in a mall parking lot trying to look up at the sky.

    Of the three stars, Zeta (ζ) was the one that really caught my attention in the 100mm refractor. The seeing was what you might call nervous — shaky, then slowly improving, suddenly shaky again, etc, etc — so at first I couldn’t see the ninth magnitude “C” component at a distance of eight arcseconds. Suddenly the seeing improved, and just as suddenly the ninth magnitude star was there, hanging on for dear life at the edge of the welded together AB pair. At 72x in an 18mm Radian, it was a stunning sight.

    Then I remembered the 11.0 magnitude “D” companion, so I used the fine-focus knob to see if I could coax it from the darkenss. It took a few seconds, but all at once, a faint glimmer of grayish-white light popped into view. As the seeing wavered back and forth, that faint glimmer of light faded in and out with it. When the seeing cooperated, it was a direct vision affair; when it didn’t, I hung onto it with averted vision.

    It was one of those delicate, artfully resolved views that make you appreciate the value of fine optics. There sat the ninth magnitude “C” companion, clearly etched into the inky blackness alongside the much brighter fifth magnitude glow of the AB duo, while nine-and-a-half times further away the wavering eleventh magnitude spark of “D” was a mere pinprick of gray-white shining through a hole in black velvet.

    I think I’ve found a new favorite!

    • Hi John. had a look at Zeta Sagitta tonight with a Tal 100r. at 66x I was
      finding it hard to seperate the AB-C pair but at 100x there was the
      C star tucked in fairly close to the primary pair, at first it was tricky
      making it out but as I studied it it became easier and as the seeing
      got better it stood out quite clear and made a lovely pair. It should be
      white but I could see a trace of yellow in it maybe just the scope.
      As the moon was just raising I did not see the D star although I did
      not look long for it as the clouds were spreading over.

      Pat.

      • Hi Pat,

        The trace of yellow matches with what I saw a week or so ago — my notes say “white with a slight yellow cast.” I’ve got a sketch of Zeta that I’ll add in the next few days. I’m trying to work through a backlog of sketches now in order to get caught up. August was a busy month for a change.

        Hope all is well on your side of the Atlantic!

        John

        Update: I just added the sketch of Zeta to the post above!
        Another Update: Just added a sketch of HN 84 and Epsilon also.

  2. Hi John, Nice sketch looking at it I think I may have seen the
    the D star just at the limit of averted vision next clear night will
    try again. Everything is well here except there are just too many
    cloudy nights.

    Pat.

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