by Steve Gottlieb
Here are my results from cruising around the sky looking the HCG's on just the last two nights (8/3 and 8/4) with my 18-inch Starmaster. Although these were all reobservations (Paul Hickson catalogued an even 100 groups), I always find it an enjoyable challenge to see how many members in each group are visible. As the cluster members generally check in at 14th-16th magnitude, relatively small increases in aperture, transparency, seeing conditions and tenacity can often pull in a new member, so you never know exactly what you will find on a given night. If you keep your old S&T magazines (or use the magazine archive at their web site), see the March '99 issue for more on these compact groups.
| HCG 73 | |||
|---|---|---|---|
| NGC 5829, the brightest member in HCG 73, was discovered by Eduoard Stephan, director of the Marseilles Observatory and well-known as the discoverer of another Hickson compact group — Stephan's Quintet. At 225x, HCG 73A appeared faint, small, slightly elongated 4:3, ~0.6'x0.45', low surface brightness with very little concentration. It's located 1.2' E of a mag 12 star and a mag 14 star lies a similar distance east. Although Stephan was using a 31-inch silvered-glass reflector he missed HCG 73B = IC 4526 just 1.3' NW. This second member was much tougher and appeared extremely faint and small, round, 10" diameter. It forms the northern vertex of an equilateral triangle with sides of 1' with NGC 5829 and a mag 12 star. Once this difficult galaxy was noticed, it was visible most of the time using averted vision and concentration at 225x. | |||
| HCG 74 | |||
| William Herschel was the first to observe HCG 74A (first listed as II 400 but now known as NGC 5910) using his 20-foot telescope with an 18.5-inch speculum-metal mirror. At first glace, NGC 5910 = HCG 74A appeared to be a fairly faint, fairly small glow, elongated 2:1 SSW-NNE, 0.6'x0.3', with a knotty appearance and brighter on the north end. With careful viewing at 225x, this glow was resolved into two nearly tangent knots. The larger and much brighter glow at the north end was HCG 74A and appeared fairly faint, small, round, 25" diameter. Barely off the SSW end was a nearly stellar knot, HCG 74B. A close pair of mag 14-14.5 stars that are collinear with the galaxy lie just 1.3' west and two mag 11 stars to the north are also collinear with this duo. Our next target, HCG 75, lies just 35' NE, in the same low power field! | |||
| HCG 75 | |||
| HCG 75A was missed by the great visual observers of the 19th century and first picked up from the Palomar Observatory Sky Survey plates in the early 1960's. CGCG 135-050 appeared faint, small, roundish though with an irregular outline, 20" diameter. Occasionally, a very faint stellar nucleus was visible with direct vision. Located 1' SW of a mag 12 star. This is a double system (with HCG 75B), although the companion was not seen with confidence. HCG 75C, situated 2' SE, appeared as a mag 15.5 star with no detectable size (only the stellar nucleus seen). It required averted to see this member clearly but the observation was easily repeatable. HCG 75D is a mere 26" NW and was only intermittently glimpsed as an extremely difficult, virutally stellar knot on line with 75C and the mag 12 star close north of the group. | |||
| HCG 76 | |||
| There are 4 galaxies here, but just three NGC designations — NGC 5941, 5942 and 5944, and this has caused a great deal of confusion in modern galaxy catalogues. Nearby NGC 5940 is unrelated to HCG 76. The three members were discovered by Lewis Swift on April 19, 1887 using a 16-inch Clark refractor that was purchased for him after the fame he received as a comet discoverer. Unfortunately, Swift's positions are often imprecise and in a compact group this can cause identification woes. The brightest member is HCG 76B = NGC 5941. At 225x it appeared as a faint, small, oval 4:3 SW-NE, 0.5'x0.35', containing a very small brighter core. NGC 5941 forms the northern vertex of a rectangular quartet with NGC 5942, NGC 5944 and MCG +01-40-002. Although visually the brightest, this galaxy did not receive a NGC designation in any modern catalogue, so amateur sky-plotting software may not make the correct identification.
At 257x, HCG 76A = NGC 5944 appeared faint to very faint, small, elongated 2:1 WNW-ESE although it took some effort to make out the elongation, 0.5'x0.25', low fairly even surface brightness. This galaxy is the second brightest in the quartet and forms the eastern vertex of this small rectangular group. HCG 76C = NGC 5942, the third brightest in the tight quartet, appeared very faint, very small, round, 20" diameter, with a very small slightly brighter core. A mag 14 star is close NW. Beware this galaxy is misidentified as N5941 in most modern catalogues. Finally HCG 76D = PGC 55316 was missed by both Lewis Swift (16-inch refractor), although it is misidentified as NGC 5942 in modern catalogues. At 257x it appeared extremely faint and small, round, just 12" diameter. | |||
| HCG 77 | |||
| At 257x, HCG 77A and 77B appeared as a soft elongated patch, extended N-S, ~20"x10". With concentration the glow appeared clumpy and at moments A or B would resolve into two 10" knots, although it was very difficult to view both simultaneously. The brighter southern knot was HCG 77A and the tiny northern knot was 77B. | |||
| HCG 78 | |||
| At 225x HCG 78A appeared faint, small, very elongated 3:1 E-W, 0.6'x0.2', with a low even surface brightness. Located 2.5' NW of a mag 13 star. Forms a close pair wth HCG 78B = MCG +11-19-016 just 1.2' SW. This faint member of HCG 78 appeared extremely small and round at first glance. In fact, all that I noticed initially was the fairly bright substellar nucleus, ~6" in diameter but with averted vision, small thin extensions were occasionally visible extending the size to 0.6'x0.2'. Although both galaxies are edge-ons, 78A has a low even surface brightness while 78B is sharply concentrated with extremely faint arms. | |||
| HCG 79 | |||
| Seyfert's Sextet is arguably the quintessential Hickson group. Five or six galaxies crammed into a couple of arc minutes. I've returned to this object many times over the past 20 years and always resolve the three brightest components (a 4th component was barely visible in a 30-inch Starmaster last summer). HCG 79B is the brightest component of Seyfert's Sextet and at 257x appeared faint, very small, slightly elongated ~E-W, 15"x10", containing a faint stellar nucleus with direct vision. A mag 14.5 star lies 1' ESE and two additional mag 14.5 stars lie close SE. HCG 79C lies just 22" west of center and is the faintest in the resolved clump of three. It appeared extremely faint, round, 8"-10" diameter. Close south of this pair is HCG 79A, another small knot that appeared very faint, slightly elongated, 15"x10".
To give credit where it's due, Seyfert's Sextet was actually discovered by Edouard Stephan in 1882. Carl Seyfert's name was later attached after a paper he authored in 1951 revealed this knot contained five or six galaxies crammed into a space smaller than our Milky Way. Although Stephan recorded this ultra-compact group as only a single object, his description "eF, vF* inv, 2 vF st nr" implies to me that he probably resolved three members though he mistook two of the nearly stellar galaxies for stars. | |||
| HCG 80 | |||
| HCG 80A = CGCG 319-038 is the brightest in a tight trio. At 223x, it appeared faint, small, very elongated 3:1 WSW-ENE, 0.6'x0.2', with a low even surface brightness. Collinear with a 30" pair of mag 14 stars about 2' S. HCG 80C is found 1.2' to the west and appeared extremely faint and small, round, just 6" diameter. The "C" component was noticed before "B" which required more effort to view. HCG 80B, a mere 30" to the south of HCG 80A was only glimpsed on several occasions as an extremely faint, extremely small knot, ~6" diameter. Back in '96, I could could almost hold this galaxy steadily with averted vision. Must by gettin' old. | |||
| HCG 81 | UGC 10319 = HCG 81 | 16 18 14.3 +12 47 43 | Size 1.1x0.4 |
| At 257x an extremely faint, small, low surface brightness glow was intermittently visible perhaps 1/3 of the time. Forms the southern vertex of an equilateral triangle with two mag 12.5 to the ENE and NNW. Only a single member or the combined glow of two or more members was seen. A few years back HCG 81 appeared elongated or possibly double, although I still was not able to resolve the glow clearly into separate components | |||
| HCG 82 | |||
| Once again, we come to a Hickson group discovered by Eduoard Stephan with the 31-inch reflector at Marseilles built by Jean Foucault. HCG 82A = NGC 6162 is the brightest member of this quartet and appeared fairly faint, small, slightly elongated SSW-NNE, 0.4'x0.3'. Contains a very small slightly brighter core with direct vision. Forms a very close pair with NGC 6163 = HCG 82B just 1.2' E and a right triangle with NGC 6161 = HCG 82C 2' S. The second brightest member, HCG 82B, is faint, small, slightly elongated N-S, 0.4'x0.3'. Overall this galaxy appears pretty similar to HCG 82A but it slightly fainter with a less concentrated core. The third brightest member of HCG 82, NGC 6161, appeared very faint, very small, slightly elongated N-S, just 0.3'x0.2'. It forms the SW vertex of a small right triangle with NGC 6162 and NGC6163. The difficult 4th member, PGC 58231, is just 48" west and is easily the faintest of the quartet in HCG 82. At 225x it appeared extremely faint and small, round, 6" diameter (just nonstellar). Visible roughly 25% of the time with averted vision. | |||
| HCG 85 | |||
| HCG 85A = CGCG 341-010 is the northwestern component of a double system with HCG 85B (40" between centers). Both galaxies appeared very faint, very small, round, 15"-20" in diameter. An extremely faint mag 16 star was intermittently visible just off the SW end. A 40" pair of mag 13.5-14 stars lies 2' north. | |||
| HCG 86 | |||
| At 225x, HCG 86A = ESO 461-007 appeared fairly faint, small, elongated 5:3 SW-NE, 0.5'x0.3', small brighter core. A mag 14.5-15 star is off the SW end. This galaxy forms the NE vertex of a triangle with HCG 86B 2' WNW and HCG 86C 3' SW. HCG 86B appeared faint, very small, round, 20" diameter, very slightly brighter core with direct vision. A mag 14.5 star is off the west side. The "B" component forms the NW vertex of a triangle with HCG 86A 2' ESE and HCG 86C 1.4' S. This latter galaxy was very faint, very small, slightly elongated, 0.4'x0.3', with a very low even surface brightness. The 4th member of the group, HCG 86D, lies 1.6' W of 86A and midway between this 86A and a 26" pair of mag 12/14 stars. This small galaxy and faintest in the HCG 86 quartet. At 225x it appeared extremely faint and small, round, just 6" diameter — essentially a fuzzy mag 15 star. The surface brightness was moderate but because the galaxy is so small it was not seen initially as I took not es on the main trio. Once noticed, though, this galaxy was not too difficult to see with averted vision. | |||
| HCG 87 | |||
| At 225x, HCG 87A = ESO 597-036 appeared very faint, small, elongated 2:1 SW-NE, 0.6'x0.3', very low even surface brightness. Located 1' SE of a mag 14/15 double star at 13" separation. HCG 87B forms a very close pair, just 1' SW of center off the SW end (collinear with the major axis). This galaxy was very faint, very small, round, 12" diameter. Although tiny, the surface brightness was reasonably high and I thought this galaxy was roughly equivalent in terms of ease of visibility as HCG 87A. | |||
| HCG 88 | |||
| This compact group was discovered by Albert Marth, who observed from Malta using a William Lassell's 48-inch equatorial reflector. This was my 4th observation of this interesting group. HCG 88A = NGC 6978 is fairly faint, fairly small, elongated 5:2 NW-SE, 1.0'x0.4', broad concentration to a small brighter core and an occasional very faint stellar nucleus with direct vision. A very faint star lies midway between HCG 88B = NGC 6977 and HCG 88A. This galaxy is the brightest in HCG 88 and furthest NE in a string of three and can be located 14' SE of mag 5.5 HD 198667 and 18' ESE of mag 6 4 Aquarii.
HCG 88B = NGC 6977 is located 1.8' NE of NGC 6978 and appears fairly faint, fairly small, slightly elongated, 0.7'x0.5', broad concentration with a slightly brighter core, occasional a very faint stellar nucleus can be seen with direct vision. HCG 88C = NGC 6976 is very faint, very small, round, 15" diameter, very low surface brightness, no concentration. This member is furthest SW in a string with brighter NGC 6977 and NGC 6978. HCG 88d was searched for at the end of the night and the best I can say is that it was suspected a couple of times, but I couldn't verify it with any certainty. This galaxy is midentified as N6975 in all modern catalogues. Last summer from the Sierra Buttes this dim galaxy was recorded as "marginal" as an extremely faint glow was glimpsed a few times with concentration and averted though I did sketch the elongation in the correct orientation (WSW-ENE) which confirmed the sighting. | |||
| HCG 89 | |||
| HCG 89A is a pretty tough object, appearing extremely faint and small, round, 10" diameter. At times it appeared larger and probably elongated as the spiral arms were glimpsed. Located close NW of a 1' pair of mag 14/15 stars. | |||
Posted on sf-bay-tac Aug 10, 2005 10:54:13 PT
Converted by report.pm 1.2 Mar 07, 2006 19:10:42 PT