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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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I would agree with 7790, as I noted it in two observations over the last two weeks with 22x85. I measured it as 2-3 arcminutes in diameter.
Skiff writes this about 7788
the cluster is nested in a group of mag.7-10 stars about 15 arcmin across. Near one of these stars is the cluster. 150mm reveals about 8 stars (Skiff observations were typically under mag 6.2 to 7.0 skies). In 250mm, 14 stars can be counted in a 1.5 arcmin area. (For comparison size, that's just a little bit bigger than the Ring nebula. At 15x, the Ring looks like a bloated star.)
So it would be reasonable to assume, at the location of 7788, you are probably seeing that group of mag.7-10 stars, and not the cluster at all.
Notes on Berkley 58
The total Vm of 9.7 is very misleading. Surface Br is mag 13.2. Skiff's notes on his observation of Be58; at low power, this group is visible as a small collection of faint stars. (Skiff's observation notes refer to a 250mm scope at 200x under mag 6.2+ skies).
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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I collect my notes here in one post from two recent observations
I had a brief opportunity to observe early this morning, and the sky was very good, so I took out the WO22x70 apo to refresh myself in the area around NGC 7790.
There is a string of 5 bright stars with the two brighest east and the two dimmest but also the closet to the west. 7790 is just ne of the center star. It was seen fairly easy as a small smudge. To estimate it size, I compared it to the two close stars towards the west. It was about 1/4 the size of the distance between that pair. I measured that pair when I came in and they are 10 arcmin apart. So, I measure 7790 as 2 to 3 arcmin in diameter at 22x.
I referenced Uranometria to try and find the other two close by clusters, Be58 and 7788. Neither could be seen.
edz
This morning, sky about mag 5.2, but very transparent.
The Nikon AE 10x50 could not see deeper than mag 9.6.
Observed vicinity of NGC7790 near Beta Cas. With Nikon SE 10x42 and ZRS 10x42 could not see 7790, but could see mist of faint stars nearby this vicinity. With Nikon AE 10x50 I saw a faint small spot for 7790 and about 10-15 arcmin NW of 7790, I counted about 6 faint stars spread over a 10 arcmin area in what was that mist. Since the 10x50AE could not see any deeper than mag 9.6 on M45, then that would establish these 6 faint stars as all brighter than mag 10. In the Garrett 22x85, 7790 was a distinct spot, and that area to the NW resolved into 12-13 stars spread over a 15 arcmin area. In the BT100 at 34x, I counted 16-17 stars over the same 15 arcmin area.
That area is centered on the location of NGC7788. However, it is much too large to be 7788. It is possible that some of the stars in the center of that mix are members of 7788, but certainly not all of them. There was no concentration noticed, even in the 22x85 or the 34xBT100, that I could call cluster 7788. (I know now from Skiff's notes that 7788 is tiny, even smaller than 7790, and in all likelyhood I did not see any part of it in that area of stars.)
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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Mark9473
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Reged: 07/21/05
Posts: 3217
Loc: 51°N 4°E
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Quote:
So it would be reasonable to assume, at the location of 7788, you are probably seeing that group of mag.7-10 stars, and not the cluster at all.
That's what I concluded yesterday also. The stars are seen individually in direct vision, then in averted vision merge together to a glow. Same for Berkely 58 especially since the location of what I plotted doesn't match exactly.
I expect to have a less ambiguous view under a better sky than yesterday's NELM 5.0.
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Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63; Docter 15x60
WO Megrez II 80 FD + Baader 90° T2 Amici
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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I am curious about what it might take to see some of these others around 7790. Obviously better sky conditions would help. Well I can't do much there, although I sometimes see a best of about mag 5.6, so I can hope for a best night. But I thought next time I set out some scopes to give these a try. 80mm might not do it. But I have 85, 100, 125, 150 and 200mm scopes so plenty of choices. I'll give a turn in that direction next time I have some scopes out and see what I can find.
Also, I thought a night of concentration with the BT100 at various powers might prove successful, so that's another option.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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Mark9473
Post Laureate
Reged: 07/21/05
Posts: 3217
Loc: 51°N 4°E
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What I meant with a less ambiguous view, is that with better sky conditions I expect not to see the glow that got me thinking I was seeing a cluster in the locations of NGC 7788 and Berk 58.
If you can manage it with your BT100's, I'd be interested to see a sketch of the area.
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Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63; Docter 15x60
WO Megrez II 80 FD + Baader 90° T2 Amici
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Crossen
member
Reged: 07/14/08
Posts: 87
Loc: Vienna
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Concerning NGC 7790, NGC 7788, and the Milky Way field around and generally west of them I quote from my original observing notes. The instrument I was using were 15x100 supergiant binoculars. The sky conditions were C+--that is, mag 6.0-6.5 at the zenith, near which the field was located:
"NGC 7790--A small patch of moderate surface brightness haze, partially resolved. The 9th mag star toward the SE of the main body is very distinct."
"NGC 7788--A ragged field concentration of mags 10-11 stars around the 9th mag central star, apparently larger than NGC 7790 to the SSE. No evidence of haze of the 12-13 mag stars crowding around the 9th mag star."
"NW of Beta Cas begins a rather broad stream of faint field stars on a pale background glow. This stream includes the line of 5 open clusters Be 58, NGC's 7790 and 7788, H21, and K12. It is fairly straight as far as 6 Cas, then arcs WNW, W, and finally SW around a distinct dark cloud. This is the ENE end of the large oval dark region to the S of the M52 Milky Way stream. A somewhat fainter star field is [within the dark region] just S of the star arc and W of NGC 7790."
NGC 7790 is very distant, almost 10,000 light-years away. It is an intermediate-age cluster with Cepheid variables. 6 Cas is the brightest member of the Cassiopeia OB 5 association, of which many of the brightest field stars in the NGC 7788-7790 must be members. NGC 7788 itself might be a member. Cas OB5 is in the foreground of NGC 7790, centered "only" about 7500 l-y away. I have never seen a really detailed photometric study of NGC 7788 (though I haven't checked the journals recently) that determines whether the cluster is really the interior knot of faint stars or the field concentration of brighter stars. In the latter case it would be simply a field concentration in Cas OB5 rather than a true gravitationally-bound cluster.
Craig Crossen
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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Observation 9-13-09 11pm to 2am sky mag 5.2
used Oberwerk BT100 with 18mm AT Paradigm for 34x100, 1.7°fov, 2.9mm exit pupil
also used TV85 with 14mm Radian for 43x85 mono, 1.4°fov, 2mm exit pupil
Tested 33xBT100 for LM and found it could reach mag 11.4-11.5.
I spent a considerable time and created a sketch which will be added after I can scan it and convert it to jpeg. I used two measured stars that span 10 arcmin to judge comparative sizes of clusters.
edit - SKETCH ADDED
Berkley 58 - not seen, no hint of haze.
NGC 7790 - brightest star on se edge of a hazy unresolved spot. Haze bordered on nw by 4 stars curved to encircle the haze spot. No resolution within the haze. Total width no more than about 4 arcmin. (A mounted Fujinon 10x50 could see this only as a small averted hazy spot).
NGC 7788 - plotted 17 stars using 33xBT100. Fainter stars centered on a brighter asterism of 3 stars in a line with a slight bend. Uranometria shows the extent of NGC7788 spans between these 3 stars. About half of all the stars I plotted are just outside the boundaries of extent plotted in Uranometria, so all may not be a part of the true cluster. My plotted stars are scattered over about 10-12 arcmin area. Considering LM test above, I would say all of these stars are brighter than mag 11, the 3-5 brightest perhaps mag 9-10. (A mounted Fujinon 10x50 could see no more than 6 stars here across the full extent of 10 arcmin, no haze noted).
Harvard 21 - This was the faintest of the clusters seen. I suspected 4 very faint stars seen with averted vision. I could tell there was something at the spot with direct vision, but could not see anything defined directly. I plotted the 4 stars in the shape of an L, long leg ne to sw, short leg towards the east. Size, ? perhaps 1-1.5 arcmin. Estimate these 4 stars as mag 11.2 to 11.4.
King 12 - stars brighter than H21, also area a bit larger, perhaps 2 arcmin. I suspected seeing 6 stars, 2 pretty faint, 4 a bit brighter. Estm 4 stars perhaps mag 10.5 to mag 11.
A bit further out past 6 Cas I also noted
King 21 - at this spot I saw what I thought was a very tiny straight line of maybe 3 stars. No real resolution of the 3, but looked longer than just 2 stars. Perhaps mag 10.5. Less than 1 arcmin long.
The TV85 at 43x could not resolve any more stars or see any more in each of these clusters than what was seen with the BT100 at 34x. I counted exactly the same 17 stars in NGC7788 and still could not see BE58.
I did stop to take a look at M52 and NGC7789. NGC7789 was resolved to perhaps 20 stars with a broad extent of haze.
BTW, I'd like to add, out of numerous things I did in last nights observing session, observed a few galaxies, compared some limiting magnitudes, split a few doubes, searched out a few new objects, etc. this little project to critically view and sketch an area I've never mapped before was by far the most interesting and if you can believe it, the most fun. Thanks for this intersting challenge. Now I need to go read up and see if my visual descriptions match what is in the written details for these clusters.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
Edited by EdZ (09/14/09 01:57 PM)
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Mark9473
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Reged: 07/21/05
Posts: 3217
Loc: 51°N 4°E
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That's a very exciting and intriguing report, EdZ. I loaded a 1/2° wide DSS image into CdC, see attached. It appears to show a rather condensed cluster for NGC 7788, actually smaller than NGC 7790.
SAC 8.0 lists NGC 7788's diameter at 9'. CdC's open cluster catalog (reference see a few posts higher up in this thread) - which was more accurate on NGC 7790 - gives the diameter for NGC 7788 as 4' which appears to match the DSS image.
Of course it is impossible to know for sure, from just a chart or image, which stars are true cluster members.
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Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63; Docter 15x60
WO Megrez II 80 FD + Baader 90° T2 Amici
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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I reviewed numerous sources on these clusters. here's what I found.
First, in almost every case, reading NSOG was reading a repeat of SkyAtlas 2000 data tables and in some cases, a repeat of Luginbhul and Skiff's observations. I'f you have already referenced L&S and SkyCat2000, you can pretty much dispense with NSOG. Also, Sky Atlas 2000 Companion, a listing of all the objects plotted in the SA2000 charts, was the least useful resource. Descriptions wanting, for this exercise only one object was mentioned. So dispensing with SA2000 Companion and NSOG, that left me with
Luginbhul and Skiff, Observing Handbook and Catalogue of Deep Sky Objects
Sky Catalogue 2000, Vol. 2, Double Stars, variables and Non-Stellar Objects
Archinal and Hynes, Star Clusters probably the definite resorce for my needs.
7790
L&S 8', 134*, using 150mm about a dozen * in a rectangle EW, in 250mm 25* within 4'x2', 5 brighest stars on west form a circlet. L&S has a full page 7"x10" plate of 7790 showing photometry. The densest concentration of bright stars is within about a 4' area and that area contains perhaps only a dozen stars brighter than mag13.
NSOG EW elongated mist, 10* mag 11 to 12, 30* in a 4'x2' area
A&H 5' Br* mag10.0, SfBr 12.0
7788
L&S 9' 20* nested in a group of mag 7-10 stars 15' across, 15* mostly east of a br*, in 250mm counted 14* in a 1.5' area
NSOG 9' 20*, a 5' concentration of mag 9-12 stars, mostly mag12-13
A&H 4' 20* Sb12.4
Be58
L&S 8' 39*, 35* mag 12+ in 5' area,
NSOG 7' Br* 11.9, using 12"@150x 3 dozen stars mag 12+ in 5' area
A&H 5' 39* br* 15.0, Sb13.2
H21
L&S 4' 6* in 250mm 5 mag 10* + 1 mag12.5 + 1 mag13
NSOG 6' 20* 5 mag 10* form an irregular pentagon 2.5' across
A&H 3' 6* probably not a real cluster
K12
L&S 2' 30*, using 250mm 18* in a haze within 2'x1', elongated EW
A&H 3' 15* br* mag10.0 Sb11.4
K21
L&S 2.5' 17*, 3* in center mag 11-12, 20* in 5'x2.5'
A&H 4' 20* br*mag10.0 Sb 12.6
Based on these data, I doubt I saw the central areaof 7788. I may have seen some of the very brighest stars, but A&H defines this cluster as 4 arcmin. I counted 17 stars across 11-12 arcmin, well outside the bounds. I trust the Archinal and Hynes data and the L&S observations more than any other.
Not surprised that I did not see Be58.
I do believe I saw the circlet in 7790
My location and description of H21 seems to indicate I saw the 4 of the 5 brightest.
I probaly saw just the very few brightest in the King clusters.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
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