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NGC 6946

NGC 6946, Arp 29, LEDA 65001, MCG+10-29-006, SPB 263, UGC 11597, Caldwell 12, IV 76, h 2084, GC 4594

RA: 20h 34m 51.4s
Dec: +60° 09′ 18″

Con: Cepheus
Ch: MSA:1074, U2:56, SA:3

Ref: SIMBAD

(reference key)

Type: galaxies (interacting), Scd

Mag: B=10.5, V=?

Size: 11.48′ x 10′
PA: ?

Historical observations

William Herschel (c.1784)

Synonyms: H IV-076

Discovered in 1798 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "cF, vL,iF, a sort of bright nucleus in the middle. The nebulosity 6' or 7'. The nucleus sems to consist of stars, the nebulosity is of the milky kind. It is a pretty object."

E. E. Barnard (1886)

"General Catalogue no. 4594"

"This nebula is described as v F in the General Catalogue. I marked it on my chart, some four years ago, as v v F with the 5-inch telescope, under fairly good conditions of seeing and altitude. I find it now almost bright, certainly not faint. It is moderate in size, round v g b M with some small stars grouped about it. Its brightness is a little less than that of the cluster G.S. [sic] 4590 [= NGC 6939] in same field with it. Observed May 28 and June 4."

Ref: [1886SidMs...5..286B]

Published comments

Supernovae

Six supernovae erupted in this galaxy; 1917 (14.5p), 1939 (11.8p), 1948 (14.0p), 1968 (11.0v), 1969 (15.4p), 1980 (11.0v).

Arp (1966)

Listed as No. 29 in Arp's "Atlas of Peculiar Galaxies" (Astrophysical Journal Supplement, vol. 14, 1966.) He remarks "Supernova once observed in tip of thick arm."

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a 10.5 mag galaxy. Their coded description reads SC,B,WDDIFKNARMS DKLNS,RI*FLD,MW OBSC CLOUDS NR.

Schmidt, K.-H. et al. (1993)

Schmidt K.-H., Priebe A. & Boller T. (1993) Nearby galaxies. Revised machine-readable version of the catalogue. Astron. Nachr., 314, 371. [1993AN....314..371S]

Other names: "U11597,ARP29". Inclination: (face-on, in degrees) 30 Total photoelectric blue mag 9.61 Total colour index .80 Logarithm of the angular diameter D25 (arcminutes) 2.06 Blue photographic magnitude 9.90 This galaxy is included in a sample of galaxies with velocity less than 500km/s with respect to the centroid of the Local Group. [Nearby Galaxies. Schmidt K.-H., Priebe A., Boller T. (Astron. Nachr. 314, 371 (1993))]

Ashbrook, J. (1968)

Astronomical Scrapbook: Spiral structure in galaxies. Sky&Telescope, June, 366.

Photo index

Photo Index by Jim Lucyk: Sky&Tel. 1/77 p13, Sky&Tel. 1/81 p21, Sky&Tel. 12/69 p392, Sky&Tel. 12/83 p549, Sky&Tel. 1/88 p115, Astronomy mag. 7/83 p82, Deep Sky #3 Su83 p16, Deep Sky #7 Su84 (back cover), Burnhams V1 p617, Galaxies (Hodge,1986) p9.

de Vaucouleurs, G. (1975)

de Vaucouleurs, G. (1975) Nearby groups of galaxies. In: Kuiper, G. (ed) Stars and Stellar Systems. Volume 9: Galaxies and the Universe. Chapter 14, p557.

p 590: "The present data on nearby groups may nevertheless help to answer the simpler question:Are there isolated galaxies? … out of the 60 galaxies in this objectively selected sample, only eight have not been associated with one of the 55 nearby groups, viz. NGC 404, NGC 1313, NGC 2903, NGC 3109, NGC 3521, NGC 6744, NGC 6946 & IC 5152. In addition there is a possibility that a few galaxies, such as NGC 1316, NGC 4594, NGC 4826 are not really members of the groups (For I, Vir Y, CVn I) to which they have been tentatively assigned. Furthermore, the reality of the NGC 5128 chain as a physical unit may be questionable; but then it is difficult to know where to stop in this 'dismemberment' of loose groups, and the local outcome of an overconservative attitude would be to exclude from consideration all but a few rich clusters and dense groups… on the other hand, several of the eight supposedly isolated galaxies might yupon further investigation turn out to be members of some of the nearer groups; in particular, NGC 404, NGC 3109 and IC 1512 should be examined for possible membership in the Local Group. Other (more remote) possibilities are NGC 1569, IC 342 and perhaps some heavily obscured systems as yet unrecognized. For example, IC 10, although long suspected, was only recently established as a Local Group member (Roberts 1962, de Vaucouleurs and Ables 1965). … to the writer's knowledge, NGC 1313 and NGC 6744 in the southern sky, and probably NGC 2903 and NGC 6946 in the northern sky, are truly isolated galaxies not associated with any nearby group, although both are in the larger Local Supercluster."

Modern observations

Walter Scott Houston

Houston notes that this spiral is easily seen in even small telescopes. It shines at 9th mag and is roughly 10' across.

Sanford (1989) Observing the Constellations

This is a low-surface-brightness spiral galaxy, showing as a softly glowing round haze with a brighter nucleus. Sanford notes that evidence of the arms is seen in 16-inch telescopes. One of the nearest galaxies.

Birkmann, Mark [amastro]

Observer: Mark Birkmann Your skills: Intermediate (some years) Date/time of observation: 7/9/99, 7:00 UT Location of site: New Haven, Missouri (Lat N 38, Elev ~700') Site classification: Rural Sky darkness: 5 1-10 Scale (10 best) Seeing: 6 1-10 Seeing Scale (10 best) Moon presence: None - moon not in sky Instrument: 30" f/4 dob, 13" f/4.5 dob Magnification: 150x-540x Filter(s): Object(s): NGC 6946 Category: External galaxy. Class: Sc Constellation: Cepheus Data: mag 9.6b size 11.6'x9.8 Position: RA 20h:34m 52s DEC +60:09' 15"

Description: Moderately bright with slightly brighter central condensation. This is a type Sc galaxy but it had the appearance of a barred spiral with a stubby arm coming off each end of the bar. The upper (sorry, I once again forgot to write in my notes where north was - hopefully the scanned drawing will help) arm was split into two amaller arms. These observations were not immediately obvious on this night. However, I noted that this structure was obvious while observing from a dark sky site with a 13" dob 7/27/90.

Tom Lorenzin

Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "11M; 12' x 8' extent; large, faint, NE-SW-oriented oblong glow with little brighter center; wraithe-like! requires field motion to detect; !good supernova prospect! 40' SE of cluster N6939."

[amastro] The Bayerishes Teleskopmeeting and NGC 6946

Greetings,

I've recently gotten back from a trip to Germany to see the eclipse clouded out) and visit some friends. One of the highlights of the trip was the Bavarian Telescope Meeting near the ancient village of Pfunz, about 30 kilometers NW of Ingolstadt. Starting the day of the eclipse and lasting until Sunday (8/15), about 75 amateurs from across Germany were in attendence. Our party stayed with Jens Bohle, a well known deepsky observer from the northern part of the country. By and large, it looked like the typical American starparty with a number of large dobs (up to 0.8 meters), high-end refractors and an assortment of Newtonians, Maksutovs and folded-optics reflectors. What was conspicuously absent was Schmitt-Cassegrains, esp. the "LX 200" types. I suspect it was a matter of optical quality over cost, since the presence of several large Astrophysics refractors and 18 -20 Obsessions negates the expense argument.

The night we stayed over, the skies were a partly clear with intermittant waves of cirrus and mid-level clouds. Limiting visual magnitude was +6.0, with a sharp light dome to the SE in the direction of Ingolstadt. Jens and I had planned an observing list of interesting and challenging objects including several of the Andromeda dwarves (galaxies), Sh2-91, Mink 1-67 and H II regions in NGC 6946. However, soft skies and other problems quickly reduced this list to NGC 6946.

Observing NGC 6946:

At 170x and 289x, the oval core region was quite prominent, and the four low contrast spiral arms were distinctly visible. Four H II regions were confirmed, of the 6 main complexs I had previously identified in Bonnarel et al., 1986 Astron. Astrophys. Suppl. Ser 66, 149

Positions and notes:

Region RA Dec Mag (v) Notes

1 20 35 25.2 +60 09 56 ~ 14 Brightest vis., easy

2 20 35 11.6 60 08 58 ~ 14 -14.5 fairly easy

3 20 34 35.5 60 11 38 15 low contrast, diffuse

4 20 34 23.6 60 10 37 >15 similar to #3

5 20 34 31.2 60 08 20 > 15.5 unconfirmed

6 20 34 57.8 60 12 44 ? did not see

I'd like to see some follow up observations on these regions with both telescopes larger and smaller than the 20-inch Obsession we used.

- Rich Jakiel

P.S. - In hunting H II regions in galaxies, I've had much better success using a combination of detailed charts/photos and high magnification than using filters. UHC and esp. O III filters ruin the view of the galaxy, and may also dim the complexes as well since there is a considerable input from stellar sources.

------------------------------------------------------------------------

I too have noticed that high power and finder charts are better than an O III for observing H II regions in external galaxies.

About 4 or 5 years ago I had really nice skies and an 18-inch scope at Mt Kobau in southern B.C. and frankly I was disappointed at the general lack of response of H II regions in the O III. NGC 604 in M33 seems to have one of the best responses of all.

My intent was to write an article on "great H II regions in galaxies to observe with an O III", but I came away with very little after several hours of observing. Without the filter at high power galaxies were most impressive. I had leisurely leafed through the Vickers CCD Atlas for targets and come up with quite a list, but alas, poor response from the O III.

One exception which does stand out is NGC 4449 in Coma. With a 16-inch and an O III the thing looked like a modest open cluster!

Alister.

------------------------------------------------------------------------

]Hi, Rich

]

]Although I wasn't looking for HII regions, here's my last description of

]N6946. Can you tell which HII knot I noted?

]

]17.5": bright, very large, 6' diameter to main body, elongated 3:2 ~E-W.

]Three arms are visible. A long bright arm is attached at the N side of the

]core and trails to the E. This eastern arm splits; a short fainter branch

]bends S following the core and a long curving bright arm terminates with a

]very faint, very small HII knot. On the W side a fainter arm shoots

]sharply to the N from the core. These outer arms significantly increase

]the diameter of the main body. Has a very large brighter middle but the

]core is just a very small brighter region close SW of the geometric center.

]A very faint stellar nucleus was seen with direct vision.

]

]Steve Gottlieb

Steve,

My guess it is likely H II knot #1. I have noted that one, and knot #2 on

several occasions using the AAC's 20-inch f/4.5.

- Rich

Brian Skiff

Ables: pair 7'.9 from center in pa345 (NNW): N 50"; pa49.

7x35mm - fntr than N6939 in Cep. circ fairly f patch w/f *s at N & S edges. mod concen? BS, 28Jun1992, Hutch Mtn.

8cm - similar to -39 (Cep), but totally unconcen and sl smlr than oc. BS, 15Sep1982, Anderson Mesa.

15cm - lg, 9'x7'. on N side of diamond-shaped *ism. four *s on neb. no detail; movement of fld helps brighten it. HM/BS, 28Jun1971, FtL.

- vdiffuse. a few *s sup. illdef uniform light. circ, pretty lg. found at 30x.

- vlg mod br glow of modlosfcbr in rich fld of *s. br triangle of m10-11 *s on S, wide pair to N. 8' diam, a fat oval elong NE-SW. wk broad concen. core is 2'.5x0'.75 bar elong N-S wkly discernable in center.halo reaches as far S as middle (Wrn) * of triangle, and 2/3 - 3/4 way to pair N. smooth texture. gx best @ 80x. needs drawing! BS, 16June1991, Anderson Mesa.

25cm - elong E-W. wide pair N. f core vis.. smmoth, indef boundary. 90x.

30cm - pretty f, vlosfcbr. elong pa45. many *s assoc. located 6' N of triangle *ism. sl concen w/30" unevenly br core region with knottings partic to S. 3'x2'.

Ferris, Bill [amastro]

[amastro] A Handful of DSOs Date: 09/10/1999 Loc.: Anderson Mesa, Flagstaff AZ Weather: Clear, calm, temps in mid 40's Scope: 10-inch, f/4.5 equatorial mount Newtonian

I visited a few old friends during my LONEOS run, last week. First up, NGC 6939 and NGC 6946, one of my favorite deep-sky pairings. NGC 6946 is a magnitude 8.8 barred spiral, its arms loosely bound. Observing at 129x (8.8 mm UWA), the galaxy covered an area roughly 13'x 5' and was elongated nearly east-to-west. The axis of its bar ran along a PA of 40 degrees. A triangle of 10th and 11th magnitude stars resides immediately to the south. A pair of stars, 10th and 11th magnitude, sits just a few arcminutes to the north.

This galaxy shows wonderful structure in moderate aperture instruments. The core region showed as an elongated brightening along the axis of the bar. Two distinct spiral arms at the eastern extent were recorded in my sketch. The eastern half also had a more mottled appearance. Three somewhat less prominent spiral arms were detected at the western boundary.

NGC 6939 is listed in the DSFG to Uranometria as a magnitude 7.8 open cluster with approximately 80 members, the brightest members shining at 11.91 magnitude. The cluster resides some 75' to the northwest of NGC 6946. Together, they make a wonderful pair for any 8-inch or larger instrument capable of producing a 90' or larger true field of view.

My sketch records the cluster with a trio of 10th and 11th magnitude stars along the northern boundary, and with magnitude 6.9 PPM 22236 just 10' to the south. Although not highly concentrated, the densest section of the cluster covered a 6'x 4' expanse, a triangle of 12th magnitude stars marking the southern extent of this concentration. My sketch shows approximately ten 13th and 14th magnitude stars at specific locations within the cluster.

NGC 7331 is often used as a landmark for the popular galaxy cluster known as Stephan's Quintet. However, the NGC 7331 group is interesting in its own right. NGC 7331 is a magnitude 9.5 spiral galaxy, its plane slightly inclined. Observing at 190x (18 mm SWA w/ Tele Vue 3x Barlow), the galaxy occupied a 8'x 2' area and was elongated along a PA of 170 degrees. A pair of 13th magnitude stars bounded the northwest extent of the nebulosity. NGC 7331 featured a stellar core with a bright surrounding core region. The northeastern edge of the galaxy had a sharper cutoff in brightness than the opposite edge.

Megastar shows four galaxies, NGCs 7335, 7336, 7337 and 7340, to the east of NGC 7331. My sketch recorded two of the four, 13.3 magnitude NGC 7335 and 14.4 magnitude NGC 7337. Both reside about 5' to the east and appeared as faint circular patches roughly 40" in diameter. NGC 7340, a 13.7 magnitude galaxy another 5' to the east, was not captured in my drawing. I may have been so focused on the intermittent glimpses of challenging NGC 7337 that the brighter neighbor escaped my attention. I've recorded this galaxy in other sketches.

I turned my attention to Jupiter, very high in the south, following my observation of the NGC 7331 galaxy group. But that's another topic for another forum.

Bill Ferris

Knisely, David [amastro]

Re: NGC 6939 and 6946. I too have enjoyed looking at these two jewels since I first ran into them in the early 1980's. Both sit within roughly a degree of each other, so they make a nice pair in the low-power eyepiece. NGC 6939 I called "the Seacrest Cluster", since at first glance, some of its stars seemed to look like a row of stadium lights at Lincoln-East High School's Seacrest Field (how's that for a naming stretch!). The Galaxy NGC 6946 seemed more like an regular spiral than SB due to the looseness of its arm structure. It seemed to have a small round nuclear region in a somewhat patchy oval of haze with faint tattered arm fragments running off the ends. It almost looks like the inner arms don't want to join up with the nucleus! In a 12.5 inch, it almost resembled a smaller fainter version of M83.

On NGC 7331, that is another favorite of mine. I like to show people M31 in binoculars then show them NGC 7331 in my ten inch, since the views are quite similar. It gives people an idea of just how far away NGC 7331 really is! Clear skies to you. --

David Knisely

[amastro] posting

I, too, enjoy looking at N6946. My notes indicate I saw it easily in a 4" f/15 Unitron refractor in 1991, but it appeared best in a clock-driven 12-1/2" f/6 on August 22, 1993. To me it looks like a faint version of M33. I'm glad for the discussions about this because I haven't really thought about looking at it since my last sighting in 1995. How often do we look for very, very faint objects and forget about these wonderful galaxies? Great object!

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