Old 06-12-2011, 04:43 PM
SteveG (Steve)
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Observations with a 48-inch dob (part 3)

Here's a continuation of some of the observations I made over the October new moon window, observing with Jimi Lowrey's 48-inch f/4 at Fort Davis, Texas. This time the focus is mainly on collisional rings and other interacting galaxies. We viewed over 5 nights and though the transparency was generally down, there were plenty of opportunities for superb views. I plan to repost these notes, along with images of these fascinating galaxies on Adventures in Deep Space.

Arp 10 = UGC 1775
02 18 26.4 +05 39 14
V = 12.8; Size 1.5'x1.5'; Surf Br = 13.5

This collisional ring galaxy was viewed at 488x. It appeared sharply concentrated with a very bright, round core 0.3' diameter. The core is offset to the SE side of a much fainter, slightly elongated 0.9'x0.7' halo. A 90 bright arc (part of the ring!) was easily visible on the NW edge of the halo. A 1993 study in AJ, 414, 154 by Charmandaris, Appleton and Marston showed this arc consists of a number of HII knots and strong star formation. A mag 14.8 star lies 1.3' W and a mag 13.5 star is 2' SW.

Arp 38 = NGC 6412
17 29 37.0 +75 42 15
V = 11.8; Size 2.5'x2.2'; Surf Br = 13.4

At 375x appeared bright, large, round, 2' diameter. Broad concentration with a large, brighter 30" core, hint of spiral structure in the halo though it was difficult to trace the arms. An HII knot or companion was easily seen superimposed at the edge of the halo on the north side (37" from center) and appeared faint, small, oval, ~12"x8". A mag 13.5 star lies 1' SW and a mag 16 star is 1.8' SW; both stars collinear with the core. A bright mag 11.3 lies 2' SE. Listed by Arp as a spiral with a "low surface brightness companion on arms", but the knot may be an HII region.

Arp 81 = NGC 6621/6622
18 12 55.2 +68 21 49
V = 13.1; Size 2.1'x0.8'; PA = 145d

At 488x the main body, which completely merges with NGC 6622, appears bright, fairly large, elongated nearly 3:1 NNW-SSE, ~1.1'x0.4'. Including NGC 6622 at the SE end, the main glow extends ~1.6'x0.4'. Fairly sharply concentrated with a bright 20" core that gradually increases to the center. At 610x, a faint spiral arm is fairly evident attached at the NNW end and beginning to wind around counterclockwise to the north side of the main glow. On the HST image (http://apod.nasa.gov/apod/ap031211.html), this is the beginning of a long tidal tail that wraps around the north side of both galaxies.

NGC 6622 appears bright, fairly small, slightly elongated, 30"x25", sharply concentrated with a bright core that increases to the center. Merged with NGC 6621 on the NW side. A mag 15.5 star lies 35" E.

Arp 118 = NGC 1143/1144
02 55 12.0 -00 10 59
V = 13.0; Size 1.1'x0.7'; Surf Br = 12.5; PA = 130d

At 488x, NGC 1144 appeared very bright, moderately large, elongated 4:3 SW-NE, 50"x35". Contains a large, very bright core that is offset to the SE side. The core gradually increases to an intense center. A mag 16.4 star is off the SE side. Forms a double system (Arp 118) with N1143, attached on the NW side where the halos merge. This galaxy is highly disrupted with a loop or ring on the NW side. An extended halo was seen on this side, but only a hint of the actual ring was seen.

Slightly fainter NGC 1143 appeared bright, fairly small to moderately large, oval 4:3 WNW-ESE, 0.9'x0.7', well concentrated with a very bright, intense core! The eastern portion of the outer halo of NGC 1143 is merged or overlaps with the halo of NGC 1144 on its northwestern side. 2MASX J02550661-0009448, listed as a 2nd "collider" with NGC 1144 in Madore's 2009 Atlas and Catalogue of Collisional Rings, lies 1.2' NW. The 2MASS galaxy appeared fairly faint, small, very elongated 3:1 N-S, 0.4'x0.15', stellar nucleus.

Arp 133 = NGC 541/Minkowski's Object/PGC 86298
01 25 44.3 -01 22 46
V = 12.1; Size 1.8'x1.7'; Surf Br = 13.2

At 488x, NGC 541 appeared bright, fairly large, round, sharply concentrated with an intense core 30" core surrounded by a much fainter halo, nearly 1.5' diameter. Just off the east side of the halo are two faint galaxies: PGC 86298 1'E and Minkowski's Object 0.8' NE. PGC 86298 appeared faint, very small, round, 10" diameter, visible continuously. A mag 17 star is 1.4' NE of center and forms an equilateral triangle with the pair.

Minkowski's Object appeared as a very faint, round, 10" diameter glow of low even surface brightness. This object is 50" NE of the center of NGC 541, just outside the halo. A good image of the trio is at http://www.daviddarling.info/encyclo...s_Object.html. The description reads " A peculiar dwarf galaxy in the constellation Cetus lying about one arc-minute ENE of the elliptical galaxy NGC 541. The latter is also a radio galaxy that has a jet of ionized plasma emanating from its nucleus. Evidence now suggests that a burst of star formation in Minkowski's Object (Arp 133) was actually triggered by the jet from the nucleus of NGC 541 because the body of the jet can be traced all the way to the region where the new stars are forming. If this turns out to be true, it will be the first known case of a jet from one galaxy influencing a neighboring galaxy and triggering new star birth. The details of just how this could occur are uncertain."

Arp 145 = UGC 1840
02 23 08.4 +41 22 20
V = 13.6; Size 1.5'x1.3'; Surf Br = 14.1

At 488x and 610x, this interesting ring galaxy (Arp 145) was composed of three components. The brightest is the "collider" component (Anon 0220+41A) at the SE edge of the "ring". It appeared moderately bright, small, round, 20" diameter, high surface brightness, containing a very small bright nucleus. The "ring" component generally appeared as a fairly large, roundish glow, at least 1.0' diameter, with an irregular surface brightness but no central brightening. A 20" pair of mag 12/13 stars are superimposed on the S and SW end of the glow and detract a bit from viewing. Occasionally, though, the "ring" popped and a brighter rim and darker center appeared, mimicking a fairly large, planetary nebula!

The third component was a very faint, extremely small "knot", perhaps 4" diameter, that was superimposed south of center. Just barely non-stellar, it formed the north vertex of a small equilateral triangle (sides 15"-20") with the pair of stars. This "knot" is classified as the ring nucleus in Madore's 2009 "Atlas of Collisional Ring Galaxies". The system is located just 3.7' SE of mag 5.8 HD 14622 and the star was kept out of the field to avoid glare. The ring and collider are given two PGC numbers, 9060 and 9062, although there is disagreement in NED and LEDA on which they apply to.

Arp 146 = PGC 586/PGC 509/PGC 510
00 06 44.4 -06 38 09
Size 0.7'x0.6'

At 610x, this collisional ring system was just resolved into two components. The larger "ring" (PGC 509) appeared as a faint, small, round glow with a low surface brightness and a diameter of 20". The "collider" component (PGC 510) appeared as a faint, extremely small "knot" on or barely off the SE end, just 8" diameter. A mag 13 star lies 1.3' NE.

Classified by Arp under "Galaxies with Associated Rings". Listed in Madore et al "Atlas and Catalog of Collisional Ring Galaxies" in ApJS, 181, 572 (2009). The "collider" also has a tidal tail or ring. This system has a redshift of z = .075, implying a distance of ~990 light years.

Arp 147 = IC 298/UGCA 57
03 11 18.9 +01 18 53
V = 14.6; Size 0.7'x0.5'; Surf Br = 13.4; PA = 126d

This remarkable pair of disrupted galaxies forms a cosmic "10" or "IC" figure. At 488x both components of this ring system were easily resolved. The eastern "collider" component (identified as IC 298A in PGC but IC 298B in NED) appeared moderately bright, fairly small, elongated 5:2 N-S, 24"x9", very small brighter core. The ring component (no nucleus) just west is a faint, small, irregularly round glow, ~20" diameter with a low but very uneven surface brightness. The rim was slightly brighter, creating a weak annular appearance, particularly on the east side. The system is located 3' NW of a mag 9.3 star.

Arp 219 = UGC 2812
03 39 53.3 -02 06 47
V = 14.0; Size 0.8'x0.7'; Surf Br = 13.2

This collisional ring galaxy appeared fairly faint with a weakly concentrated "bar" elongated 3:1 or 7:2 WSW-ENE, ~40"x12". The well-defined bar is surrounded by a very low surface brightness halo, but a brighter rim was not seen. The collider companion, 2MASXJ03395491-0207241 (B = 17.9), was just visible 45" SE. It appeared extremely faint and small, round, 8" diameter. UGC 814 lies 5.5' NE. It appeared moderately bright, fairly small, round, 35" diameter, broad concentration with a brighter core. An isosceles triangle of mag 14-15 is close NE.

II Zw 180 = PGC 69042
22 31 03.9 +00 16 40
V = 15.9; Size 0.3'x0.2'

II Zw 180 was described by Zwicky as a "Red fuzzy compact with long blue jet [north-north-west]. At 488x and 610x the galaxy appeared very small, round, 12" but easily visible with a fairly high surface brightness. It contains a moderately bright, quasi-stellar nucleus surrounded by a small round halo. Once in awhile, Zwicky's "jet" was just visible as an extremely faint extension to the north. This companion is catalogued as SDSS J223103.49+001659.2 = PGC 1161884, and LEDA lists a B mag of 18.5 with dimensions 0.45'x0.1'.

"Crossed Galaxies" = PGC 70994
23 18 12.4 +04 11 06
Size 0.5'x0.3'; PA = 110d

At 610x the "Crossed Galaxies" appeared fairly faint, fairly small, irregularly round. With careful averted vision, very faint extensions were often seen extending NW-SE. The central part appeared a bit brighter than the listed magnitude (B = 16.8). A mag 14.4 star lies 1' NE and a right triangle of mag 12.5/13.5/14.5 stars lies 4' SW.

Zwicky's description reads "Crossed galaxies, post-eruptive or result of the crossing of a compact galaxy ... through an edge-on spiral". Listed as a possible polar rIng galaxy in the 1990 catalogue "New Observations and a Photographic Atlas of Polar-Ring Galaxies" with the elongated structure at PA ~125 (NW-SE) the "disc" and the crossing "polar ring" at ~64 (SSW-NNE). A 2000 paper in Astronomy Letters, vol. 26, p. 757-762 by Karataeva eta al ("A Study of the Object ZGC 2315+03: A Candidate Polar Ring Galaxy") concludes the pair is more likely projected onto one another, although the redshifts are nearly identical in NED.

NGC 985
02 34 37.4 -08 47 10
V = 13.4; Size 0.9'x0.9'; Surf Br = 13.0

At 488x and 610x this disrupted, collisional ring galaxy revealed its structure. A very bright, sharp stellar nucleus is offset to the SW side of the halo. The moderately large halo appears as a 0.9'x0.7' oval or a circle that was squashed along the south and southeast edge, near the nucleus. With averted vision, the brighter rim was noticeable and the galaxy appeared as a ring with a darker center and a "diamond" (the Seyfert nucleus) attached on the SE side. The ring appeared similar to a faint annular planetary. A mag 18 star is at the north edge of the rim. 2MASX J02343785-0853042, an easily visible galaxy (B = 16.6), lies 6' S.
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Old 06-12-2011, 05:09 PM
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DavidU (Dave)
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Nice report.
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Old 06-12-2011, 06:11 PM
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Paddy (Patrick)
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Green with envy!!! What a great account of stunning observations. Thanks for sharing them with us Steve. Oh, to see such things so clearly!
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Old 07-12-2011, 06:11 AM
SteveG (Steve)
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Originally Posted by Paddy View Post
Green with envy!!! What a great account of stunning observations. Thanks for sharing them with us Steve. Oh, to see such things so clearly!
I appreciate the comments. For accuracy's sake, I mentioned that Arp 146 was a distance at 990 light years -- uh, that's off by a factor of 10^6. Make that 990 million light years.
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Old 07-12-2011, 02:49 PM
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kustard (Simon)
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I'm living vicariously through your eyes at the moment with these reports
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Old 07-12-2011, 03:49 PM
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Hi Steve,

Thanks for the detailed report. It is further testimony to what a fabulous instrument the
48" turned out to be.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
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Old 07-12-2011, 05:59 PM
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astroron (Ron)
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Thanks for the report Steve,I followed your report through my "Arp Atlas of Peculiar Galaxies" and images from Aladin.
Your reports surely give one a wish for more aperture.
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