Object of the Week, September 20, 2020 -- Hickson Compact Group (HCG) 99

Hickson Compact Group 99

Members: 5
Total diameter: 2.3'
Magnitude: V ~ 13.7 to 16.6
Distance: 400 million l.y.
RA: 00h 00m 43.7s
Dec: +28° 23' 20"
Constellation: Pegasus

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Hickson Compact Groups (HCG) have always been among my favorite deep sky targets. The catalogue contains 100 compact groups, published by Paul Hickson in 1982 based on the POSS1. All groups contain at least 4 members (though many have a "member" in the foreground or background) and satisfying criteria for compactness and isolation. Always fascinating to see several galaxies packed into a tiny space. And HCGs provide a seemingly endless number of challenges -- there's always a dim member or two (maybe more!) that eludes me, but that's the fun. You can always hope with better conditions (or perhaps a bit more aperture) you'll snag that elusive member.

Several of the more famous groups have been chosen as OOTW: Stephan's Quintet (HCG 92), Seyfert's Sextet (HCG 79), Copeland's Septet (HCG 57), and HCG 68.

HCG 99 lies within the great square of Pegasus, just 1.8° WSW of Alpheratz (Alpha Andromedae) and 11' west of 6.8-magnitude HD 224895. The 5 members probably form a physical group at 300 million light years, although the redshifts vary by about 10%. The easiest member due to it high surface brightness is HCG 99B (UGC 12899), with a V magnitude of 13.7 and should be visible in 8". HCG 99C (CGCG 499-33) is attached at the west end, only 0.6' between centers, making a striking close pair.

I wrote an article that just came out in the November issue of Sky & Tel on the unknown discoveries of E.E. Barnard while he was observing with a 12-inch refractor at Lick Observatory. Guess what? Barnard discovered HCG 99B and 99C visually in January 1889. As his primary interest was searching for comets, he never measured an accurate position or published the discovery -- otherwise, these two galaxies would have IC designations (the NGC had just been published). But along with other members of the group, they weren't known until the galaxy surveys in the 1960's based on the POSS1.

Interestingly, Barnard missed HCG 99A, which is the largest member of the quintet but is masked by an 11th magnitude star at its south end. In my 18", I described it as a "very faint, phantom streak extending north of a mag 11 star. Not noticed initially (picked up HCG 99B first), but once detected was fairly easy to view, although the brighter attached star detracted from viewing."

Tiny HCG 99D and 99E are much smaller and more challenging. At 16th magnitude, HCG 99D is a nice challenge for an 18" scopes under dark skies. In my 24", I called it "extremely faint and small, round, ~10" diameter." At V = 16.6, HCG 99E is the smallest and faintest member of the quintet and would only pop in my 24" as a barely non-stellar speck.

If you take a look at HCG 99, also check out 14th magnitude CGCG 499-026 about 13' SW. It shares the same redshift with HCG 99, so is probably a member of the same group. An uncatalogued unequal double star is off its east end (6" separation) and 3' east of CGCG 499-026 is 15th magnitude LEDA 1831453, a low surface brightness spiral.

As always,

"Give it a go and let us know!
Good luck and great viewing!"

I have a soft spot for Hickson groups as well. My notes with my 20" from SQM 21.0 skies in Spain on November 8, 2015, read (with the Hickson letters added for this comment)

"After a star hop I see a faint glow at 83x. At 320x I see three galaxies. At 545x I see UGC 12897 (99A) next to a bright star. UGC 12899 (99B) is the easiest of all. MCG +05-01-021 (99C) lies next to UGC 12899 along its major axis on the side of UGC 12897 and is the hardest of these three galaxies. To the south east lies a triangle of two brighter and one fainter star which I can see well. In the circle formed by the three galaxies and the triangle I occasionally see a faint glow. When I move the telescope, this glow moves along so that's PGC 60 (99D). I think I see PGC 57 (99E) as a single glow combined with a very faint star as well. Again visible as a faint glow that moves along when I move the telescope."

I didn't look for other galaxies in this field.

I observed HCG 99 with my 18" f/4.5 Obsession on Sunday night from a location called "Laguna Mountain", about 2 hours south of San Jose, California. The skies were so-so and the seeing was poor. There could have been some haze in the sky. An observer observing about 15--20 miles away reported an SQM reading of 21.38. I note (a) as appearing brighter than (b) for some reason.

HCG 99: The field immediately shows two clumps (b) and (c). (a) is not seen at first because of the proximity to the star. (a) appears the brightest, and its elongation is clearly seen. (b) is only slightly elongated, and the second brightest. Both (a) and (b) can be held continuously with averted vision. (c) is faint, but not too hard. It can be held about 50% averted. (d) is very difficult, and I got 7--10 distinct pops of it. (d) is impossible to hold steady, I may have longest held it for about 2 seconds on one occasion. (e) was not seen, maybe something was felt there 2--3 times, but too weak to conclude.

I looked through my scattered logs (I have been terrible about keeping logs) trying to see if I had other notes but couldn't find any (Steve mentions he may have shared views at a Calstar star party, but I couldn't find logs from Calstar).

Update: The eyepiece used was a 6mm Delos, which gives 343x on my telescope.

I seem to have only one observation of Hickson 99, and it's from the early 2000's with my old 20-inch. My notes are sprinkled with the magnitudes of the individual galaxies, which are from an old Astronomical League observing book I don't have handy right now. My notes and quick sketch:

"Wow! Galaxy "E" is the faintest object I know I've seen: 17.3. Galaxy "D" is 16.7, and it's relatively easy to see - the sky is clear, dark and steady! Next to galaxy "E" is a star that's about the same brightness making this a very faint double. Galaxy "A" looks a bit dimmer then "B", perhaps because it's so close to a relatively bright star. 500x."

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Hopefully I can take another look - and make a more detailed sketch - if next month is relatively smoke free.

Hi All,

Here is how I saw the group with a 10" and a 25" scope.
All details at:
http://www.deepsky-drawings.com/hcg-99-t254/dsdlang/en

Clear sky
Bertrand

Attachment 4005

Nice OOTW!

I observed this group several times. However, the most recent time was at the 2011 OSP under NELM 7.0+ skies. That was the year I decided to borrow, at the time new, TeleVue 6mm Delos eyepiece. I compared it with my 6mm Ethos and 6mm ZAO-II with my 22" f/4 reflector.


Here are some brief observing notes (all with my 22")

With the 6mm ZAO-II at 383x (copied/edited from my website)
All five members seen. I’ll focus on component D and E as the first three are blazing.
Component D - Very faint, very small round glow held 100% of the time with averted vision. Component E – Very faint, very small round glow held almost 100% of the time with averted vision.

6mm Delos
I could hold component E about 75% of the time and still could hold component D 100% of the time.

6mm Ethos
I could hold component E about 50% of the time and component D less than 100%, about 90% of the time.


Interesting observation and at two other observers confirmed my observations. One is very experienced (Daniel Mounsey) and Gregg Blandin of Crossbow Platforms was the other observer.

Cool find. Did you search the scanned original observing notes of Barnard?

I found two entries within my Hickson-project.
With 16-inch I could catch the three brightest members. With a 36-inch I could catch d and e with direct vision. Interestingly c shows details as a bar and I estimated the ring structure. Unfortunately only a sketch with 16-inch here.

sketch: 16", 225x, NELM 6m5+
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home

Barnard generally only made very rough diagrams to indicate the position of nebulae, but here's his diagram, along with a similarly rotated DSS1 image (MegaStar) to show his 3 stars (indicated as mag 9.5 but much fainter) and the close pair he discovered (HCG 99B and 99C). The mag 9.5 star at the top of his diagram is attached to HCG 99A (missing).

Steve

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In my 12" New Moon dob under SQM 21.2 -21.3 (sub par for this site but the best night from a run of three) I barely detected a faint elongated glow for HCG99 at 188x, slight variation in brightness which was probably 99B/C on one end with 99A+star on the other. Better conditions or higher power might have at least separated the seemingly connected glow.