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Cosmic Challenge: The Deer Lick Group


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Cosmic Challenge: October 2019

The Deer Lick Group

 

Phil Harrington

This month's suggested aperture range:

6-inch (15 cm) to 9.25-inch (23 cm) telescopes

 

 

Target

Type

RA

DEC

Constellation

Magnitude

Size

Deer Lick Group

Galaxy group

22h 37.3m

+34° 26.1'

Pegasus

--

~6' span

 

The autumn sky abounds with little bundles of galaxies scattered throughout its stars. One of the best known is the group of 7 galaxies that surround the magnificent spiral NGC 7331 in Pegasus, the Flying Horse. An observer could easily spend an hour or more just soaking in all that this small patch of sky has to offer.

Above: Autumn star map. Credit: Map adapted from Star Watch by Phil Harrington

Above: Finder chart for this month's Cosmic Challenge.
Click on the chart to open a printable PDF version.

 

NGC 7331 is reason enough to hunt down the group. Under dark skies, it makes a great challenge object for a pair of 50-mm binoculars. To find it, center on the star Matar [Eta (η) Pegasi]. Matar is often portrayed as one of the horse's front knees, just northwest of Sheat [Beta (β) Pegasi] in the Great Square. Look 5½°, or about a binocular field of view, to its north-northwest for a pair of orangish 6th-magnitude stars. Drop a degree back and NGC 7331 should be centered in view.

This galaxy takes on a life of its own through backyard scopes. At 84x, my 8-inch reflector shows an intense, perfectly circular galactic heart enveloped by the elongated whisper of the galaxy's spiral-arm halo, which is oriented north-south. Careful study through the same instrument at 119x reveals a subtle, mottled texture to the halo. As shown in the sketch below, a prominent dust lane along the western edge of the spiral-arm disk also comes into view and causes the core to appear slightly off-center. Can you make out any of the lane's blotchiness or hints of the spiral arms themselves that appear so prominently in photographs? 

Four fainter galaxies are found just to the east of NGC 7331. Together, they collectively form the "Deer Lick Group." NGC 7331 represents the salt lick enticing the quartet of deer -- NGCs 7335, 7336, 7337, and 7340. In other circles, these four are known as "the Fleas," perhaps in search of a deer to call home.

Above:  NGC 7331 surrounded by some of the Deer Lick Group galaxies as seen through the author's 8-inch (20cm) reflector

 

Target

Type

RA

DEC

Magnitude

Size

NGC 7325

Double star

22 36.8

+34 22.0

14, 15

15"

NGC 7331

Galaxy

22 37.1

+34 25.0

9.4

14.5'x3.7'

NGC 7333

Single star

22 37.2

+34 26.0

15

--

NGC 7335

Galaxy

22 37.3

+34 26.9

14.4b

1.7'x0.7'

NGC 7336

Galaxy

22 37.4

+34 28.9

16.8

1.1'x0.4'

NGC 7337

Galaxy

22 37.4

+34 22.5

15.2p

1.3'x0.9'

NGC 7338

Double star

22 37.5

+34 24.8

14

--

NGC 7340

Galaxy

22 37.7

+34 24.6

14.7p

1.1'x0.7'

 

Fleas or deer notwithstanding, the most prominent of the four is NGC 7335, a tight-armed spiral spanning just 1' x 0.4'. Look for its faint, oval blur 3½' to the northeast of NGC 7331. NGC 7336 is situated 2' further north, on the other side of a 13th-magnitude field star. Spotting it through a telescope in the 6-to-9.25-inch range is difficult, if not impossible. Indeed, it puts up a valiant fight even through my 18-inch. Use averted vision to pick out its vague, elliptical form. If you have gifted vision, a top-notch telescope, and perfect conditions, you just might spy it.

Southeast of NGC 7331's core is an obtuse triangle of three 13th-magnitude field stars. If you can find them, then you have also found the home of NGC 7337, just west of the triangle's apex star. Although its spiral arms span about an arc-minute, only the galaxy's very compact core will likely be detectable through amateur telescopes.

The easternmost deer, NGC 7340, strikes me as the second brightest. Its disk appears almost perfectly round, with just a hint of a brighter core. You'll find it just south of a second, brighter obtuse triangle of stars, this one oriented north-south.

NGC 7331 may look like the mother duck, and the others all ducklings following in line, but in reality they are at far different distances away. NGC 7331 is estimated to lie 39.8 million light years from the Milky Way, while NGCs 7335, 7337, and 7340 are some 300 million light years away. The last, NGC 7336, is another 100 million light years further still. But NGC 7331 may not be a loner after all. Studies conducted in the mid-1990s indicate that NGC 7331 may be gravitationally associated with NGC 7320, a dim galaxy 5' to the southwest. NGC 7320 is a member of a most peculiar gang of galaxies known as Stephan's Quintet. Stephan's Quintet was our featured challenge in October 2017.

Incidentally, if you check the original New General Catalog, you will find five other entries in the immediate vicinity: NGCs 7325, 7326, 7327, 7333, and 7338. None is a distant galaxy, however. Rather, each is a misinterpreted close-set double star, a faint individual star, or perhaps a figment of a tired astronomer's imagination. Of these, NGC 7325 is the brightest of the "missing" deer, although it is nothing more than a very faint double set 4½' southwest of NGC 7331's core. Even its brighter component, shining at 14th magnitude, is beyond the grasp of many a backyard telescope.

Until next month, remember that half of the fun is the thrill of the chase.  Game on!



About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy.  A revised, second printing of Cosmic Challenge: The Ultimate Observing List for Amateurs is now available with updated data tables and charts for finding various solar system objects, such as Pluto and Vesta, as well as improved renditions of the many eyepiece sketches that accompany each of the 187 challenges encompassing more than 500 individual objects.  The book is available from Amazon.com.  Visit www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2019 by Philip S. Harrington.  All rights reserved.  No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.

 


  • okiestarman56, John O'Hara and kt4hx like this


3 Comments

Photo
Dave Mitsky
Oct 02 2019 12:51 AM

The NGC 7331 group is certainly a good target but unfortunately it has the DSO nickname that I find the silliest, even more so than some of the doozies in Hidden Treasures, since it was named after an observing site in North Carolina.

 

http://www.skiesbyaf...es/NGC7331.html

 

https://www.google.c...2!4d-82.1212281

    • PhilH, okiestarman56 and Augustus like this

Agreed, Dave.  But I don't name 'em, I just write about 'em. :lol:

    • Dave Mitsky, okiestarman56 and Augustus like this
Photo
Arcticpaddler
Oct 02 2019 01:24 PM

The Deer Lick Group, along with nearby Stephan's Quintet, are objects that I go back to again and again--and spend a lot of time at the eyepiece each time.  From my experience, you should save these objects for the darkest, most transparent nights, and use the highest magnification that conditions allow. 

 

A complicating factor with the "fleas" is the wide range of magnitudes listed for these objects in various sources.

 

I have seen 3 of the "fleas" with my 8-inch SCT at 182x--and suspected the fourth (NGC 7336)--but of course will wander back there on the next excellent night... 

    • PhilH, okiestarman56 and Augustus like this


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