• 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.

On The Algol Road: Σ 369, AG 67, Epsilon (ε) Persei

After spending a nerve-wracking and ghoulish evening carousing with Algol and its companions a few weeks ago, I turned my attention to perusing its specterous neighborhood for other interesting stellar objects that might be lurking in the darkness.  And that’s when I discovered a little know interstellar highway which goes by the name of The Algol Road.

In order to locate this starlit road, all you have to do is extend a line east from Algol to Epsilon (ε) Persei, a 2.89 magnitude blue-white star that occupies the road’s opposite end, where it competently guards Perseus’ eastern approaches.  Epsilon (ε) is a tricky little triple star, but before reaching it, you’ll trek past two other immensely intriguing multiple stars.  The first stellar distraction to be found along The Algol Road is Σ 369, an attractively tight seventh magnitude pair.  The second scenic attraction is the odd-prefixed AG 67, a uniquely aligned triple star in a stunning field of near matches.

So toss a few eyepieces into your traveling bag, grab a warm coat, and hop aboard my star-dusted traveling machinery – our first stop is a mere 705 light years away.

We’ll put Perseus in context first . . . . .  (Stellarium screen image with labels added, click for a larger view).

We’ll put Perseus in context first . . . . . (Stellarium screen image with labels added, click for a larger view).

 . . . . . and then we’ll take a closer look at the Algol to Epsilon (ε) Highway, with the locations of our three stars plotted for your star-hopping pleasure.  (Stellarium screen image with labels added, click once again to enlarge).

. . . . . and then we’ll take a closer look at the Algol to Epsilon (ε) Highway, with the locations of our three stars plotted for your star-hopping pleasure. (Stellarium screen image with labels added, click once again to enlarge).

Σ 369                           HIP: 15282   SAO: 38700
RA: 03h 17.1m    Dec: + 40° 29’
Magnitudes: 6.83, 7.72
Separation:  3.4”
Position Angle: 29°  (WDS 2010)
Distance: 705 Light Years
Spectral Classification: B9, A0

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

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

Now there are two ways to get to our first star.

First, you can start at Algol and traverse the highway for a distance of about two degrees due east.  Or, if you’re new to these parts, you can cheat a bit and use Rho (ρ) and Omega (ω) Persei as pointers.  If you draw a line from the first one (ρ) through the second one (ω) and then divert it very slightly to the north and extend it again for the same distance, you’ll find yourself passing over the top of 7.0 magnitude HIP 15065 and landing right on target at our first destination, Σ 369.  In fact, if you’re using an 8×50 or 9×60 finder, I recommend you pause and linger over this view for a few minutes.   Algol, Rho (ρ), Omega (ω) and Σ 369 will all fit quite comfortably into your finder field of view — add them together and you have a very satisfying configuration of starlight.

But of course we came here to pay Σ 369 a visit, so when you’ve had your fill of lingering, we’ll break out an eyepiece that will deliver something on the order of 100x for our six inch refractor and see what we can see.

Two pin-holes in black velvet! (East & west reversed to match the refractor view, click for a better view).

Two pin-holes in black velvet!  (East & west reversed to match the refractor view, click for a better view).

This is a tight pair – no surprise given its 3.4” separation – but since the two stars are within a magnitude of each other, they’re not difficult at all to pry apart.  In fact, the first time I saw them was in my 80mm f/15 Mizar refractor in very poor seeing conditions – so poor, in fact, I never was able to apply enough magnification to split the pair, but I did eke out a a hint of duplicity.   In a refractor, they have that classic pin-hole-in-black-velvet-appearance which is so characteristic of two closely spaced stars of similar magnitudes.

And they’re a pleasing white pair of stars as well, although in his comprehensive survey of Struve’s stars, Thomas Lewis described the secondary as “ash.” (p. 87 of this book).   Haas describes them as a “bright white star with a shadowy greenish spot almost touching it” – but when I asked the shadowy Mr. Green about that, he said he had never been there.    (This is Mr. Green:  ➡    :mrgreen:)

Lewis - page 87Surprisingly, William Herschel seems to have missed this pair, but the senior Struve did happen across them in 1829.  In his initial observation, he recorded a separation of 3.25” and a position angle of 28.8 degrees, both of which are generally echoed by later nineteenth century observations, as you can see in the thumbnail at the right from the Lewis book.  So given the 2010 Washington Double Star (WDS) figures of 3.4 arc seconds of separation and a position angle of 29 degrees, the primary and secondary have barely moved at all in relation to each other in the intervening 181 years.

Let’s move east now to a very rare view.  The best way to get where we’re going is to draw a line from Algol to our present Σ 369 location and then extend it further east by the same distance.  In your finder, that will bring you out just short of two faint stars, 7.0 magnitude HIP 16186 and 6.7 magnitude AG 67.

And be ready for a surprise.

AG 67                         HIP: 16220   SAO: 38870
RA: 03h 29.0m    Dec: +40° 11’
Magnitudes   AB: 7.49, 10.37    AC: 7.49, 11.10
Separations  AB: 23.80”             AC: 52.60”
Position Angles   AB: 349°  (WDS 2002)     AC: 351°  (WDS 2009)
Distance: 673 Light Years
Spectral Classification: G5 (A only)
(AG is Astronomische Gesellschaft)

Now I really had to look twice when I first cast eyes on this field because there were two very obvious clusters of stars competing for my attention:

AG 67 is the cluster of three stars at the center of the field, and in the west corner (at the bottom) is HIP 16186 with a pair of fainter non-related friends.  (East & west reversed, click for a larger view).

AG 67 is the cluster of three stars at the center of the field, and off to the west (at the bottom) is HIP 16186 with a pair of fainter non-related friends. (East & west reversed, click for a larger view).

AG 67 is supposed to be the featured attraction in this sketch, but it’s surrounded by a lot of other attractive company, too.

First, there’s seventh magnitude HIP 16186 and its two attendants at the west edge of the field, which really confused me until I grabbed my notes and pinned down position angles.  Then there’s a curving trio of tenth and eleventh magnitude stars several arc minutes northwest of AG 67, plus a very tight triangle of twelfth magnitude stars northeast of those that make themselves known as a difficult-to-resolve shadowy presence.  I can’t recall ever seeing anything quite like this field of stars, mainly because of the similarity between AG 67 and HIP 16186.  And as you can see in the condensed view in the photo below, this is a field rich in galaxies, although I didn’t see any of them — the brightest one in the field was well out of my reach at fifteenth magnitude.

STScI Photo, click to enlarge.

STScI Photo, click to enlarge.

AG 67’s 7.49 magnitude primary struck me as white, but surprisingly I found more color in the midst of HIP 16186’s retinue. Although that star was an intense white, I was able to detect a very subtle blue hue in the 10.2 magnitude star southwest of it (to the right in the sketch).

Last, but hardly least, is Epsilon (ε), also a triple, situated at the end of the Algol Road.

Epsilon (ε) Persei   (Σ 471)   (AB is H II 22)   (D is ARN 59)       
HIP: 18532   SAO: 56840
RA: 03h 57.9m    Dec: +40° 01’
Magnitudes:  AB: 2.85, 8.88   AC: 2.85, 13.90   AD: 2.85, 9.25
Separation:   AB: 8.70”            AC: 79.90”            AD: 162.90”
Position Angles    AB: 10° (WDS 2008)  AC: 10° (WDS 2009)  AD: 146° (WDS 2003)
Distance: 538 Light Years
Spectral Classification:  “A” is B0.5, “B” is A2, “C” is K7, and “D” is A5

To quote my notes, what we have here is a “blazing beauty.”  I saw all white everywhere I looked (lots of it), but Haas saw a “brilliant whitish lemon star almost touching a little dot of rich cobalt blue” in a 125mm scope at 200x.  On page 91 of The Bedford CatalogAdmiral Smyth described Epsilon (ε) as a “fine and delicate object” and saw pale white and lilac in his 5.9 inch Tulley refractor.  Lewis recorded “greenish white, blue” (p. 104 of the earlier link), and . . . . . . .

Herschel Excerpt

. . . . . . . the star’s discoverer, William Herschel, described it as “w.” [white] and “d.” [dusky] when he first looked at it on August 2nd, 1780, at a magnification of 222x.  (1782 Catalog, scroll halfway down to “Catalogue of Double Stars”)

When I looked at Epsilon (ε), the 9.25 magnitude “D” companion (the third star referred to above by Herschel) stood out rather well in this sparse field, but the 13.9 magnitude “C” sibling was absolutely nowhere to be seen.

 With six magnitudes of difference between them, you have to look closely to see the 8.9 magnitude secondary nestled up closely to the 2.9 magnitude primary, but once you have it, it’s an absolutely beautiful sight.  (East & west reversed, click for a larger view).

With six magnitudes of difference between them, you have to look closely to see the 8.9 magnitude secondary nestled up closely to the 2.9 magnitude primary, but once you have it, it’s an absolutely beautiful sight. (East & west reversed, click for a larger view).

It’s far enough out there, at 79.9 seconds of arc from the primary, that it should be visible in a six inch refractor — and at the same position angle as “B”, I really expected to see it.   The seeing on this particular night was horrible, though, so I had no luck trying to penetrate the evil veil of scattered light drawn over it.

Epsilon Persei “A” has the distinction of being one of the hottest stars in the sky visible to an unadorned eye.  It burns at a “mere” 27,600 Kelvin (49,220 degrees Farenheit), which means it’s about 5.5 times hotter than the sun (5800 K., or 9980 F.)   Size wise, compared to our nearest star, the radius of Epsilon “A” is seven times greater than the sun, and it exceeds the sun in mass by a factor of fourteen.  Add all that up and what you have is a star racing toward supernovae status in a few million years.

So time’s a wastin’ – you better get out there soon and take a look at this blazing beauty.

Clear Skies!  😎

Advertisements

4 Responses

  1. Saw Eta Per. last night just as “B” and “D” looked in your excellent sketch. A fine view for the first time in my ED 80 at 100X. With luck i will have another go tonight and try to get the other two on the Algol road. Also liked your explanation of where The Ghoul`s name came from. Amazing that the English and Arabic names are so similar. Really hope you get better skies real soon. Regards, rich.

    • Hi Rich,

      Hope you get a chance to look at Σ 369 with your 80mm — I would be interested in whether you can split it at that aperture. Based on my observation, it should be possible, but the seeing was just too poor on the night I described to get a firm split.

      And don’t miss AG-67 — it’s a subtle little beauty with HIP 16186 in the same field.

      John

  2. Hi John, I got a long good look at Z 369 last night which confirned “Calsky”s forecast of a clear and steady chance for astronomy. Two equal white stars split by one of their own diameters. Lovely. I see several such equal doubles where you can just fit another star between them, over the year. Mostly I get these targets from this site. Usually for a “first” I try for the PA and make a note of the power used. For the moment all I can say it was either 100x or 200x. I used your tip of drawing a line through rho and omega and where it crossed the line from Algol to Epsilon -that`s where i looked. Bang! Next time i will try for more details and also report on AG 67. BTW how do you get the correct Struve symbol on your keyboard? Hope you get the “seeing” you deserve, regards rich.

  3. “Two equal white stars split by one of their own diameters” — by Jove, you got it, Rich! Good work, and that’s a great description of that pair. And for those who haven’t seen it, their diameters are pretty darn small, so don’t expect a large slice of black sky.

    On the Struve symbol, the screen I use to type up the posts has access to the Greek symbols, but that’s not accessible to those leaving comments here. What you can do, though, is go up to the post that has the symbol you want, copy it, and then paste it into your comment. I’ve done it from the comment screen several times.

    There’s also a way to get those symbols using the ASCII code, but you need to know the numbers for them — and I don’t have that handy. I’ll send you an email with a Word document that has all the Greek characters — you can copy them from it as well.

    Got aced out by fog tonight, on what was supposed to be a clear night. Rats again!

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: