Wow! What a night of observing after long...

Hi folks

I managed to go to my usual observing site in the Texas Hill country on Monday night. Here are some of the less chased targets that might be of interest to this great forum:

Hodge globulars in the Fornax dwarf galaxy:

I started out with these 5 globular clusters that seemed within reach. I didn't even bother trying for the other 6th one not listed in Hodge -- maybe I should? Has anyone seen it with an 18" or similar aperture?

NGC 1049:
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Had seen this before with 17.5" from south India. But here's from this session: At 66x, it looked stellar, virtually no diffusenss. At 103x, it started appearing somewhat non-stellar. At 205x, it was distinctly non-stellar. Easiest of the 5 Hodge GCs. High surface brightness and quite condensed.

Hodge GC 4:
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This was the second easiest of the five. It was detected just by bringing it into the FOV, but without knowing precisely where to look at all. Distinctly non stellar at 205x. Just about as condensed as NGC 1049, if not just a bit more condensed. High surface brightness.

Hodge GC 5:
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This was somewhat similar to GC 4, except I would rate it a bit more fainter. Similar condensation to GC 4.

Hodge GC 2:
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This was somewhat substantially fainter than the rest, but still not quite difficult. This one required me to know where to look. It was a much more diffuse, almost uniform glow; felt somewhat larger than NGC 1049. It took me about 10 seconds to realize that it was in the field.

Hodge GC 1:
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This was at the very edge of visibility. Extremely faint. By far the hardest of the 5 globulars. Sensed a repeated number of times using "Jimi's trick" (of rocking the focus) after knowing the precise position. The ultra-precise position was predicted from observation and validated against DSS, thereby confirming the observation. The best view was with a 14mm Pentax XS at 147x (Thank you, Jimi!! It's a wonderful eyepiece). Next best view was with a 16mm Abbe ortho from University Optics at 128x. Only sensed at moments, "flashing" in and out.

Abell 31:
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I picked this of "Adventures in Deep Space", probably from a report by Steve. Looked very faint on the DSS, but the OIII made it easy as it is with planetaries. The DSS was very misleading, as that was definitely not where I observed the nebulosity in the eyepiece. This post from CN has a blinking H-alpha / OIII image, and the OIII certainly matches what I have in my logs!! -- http://www.cloudynights.com/topic/31...11-in-ha-oiii/
It was faint, but definitely visible in my 18" at 20mm Pentax XW + OIII filter.

Arp 142:
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Again picked off of one of the Arp samplers on "Adventures in Deep Space". I could not see the faint edge-on that looks like a comet because of the foreground star on it (I couldn't find a desgination for this one...). But NGC 2936 and NGC 2937 were easy. With some care, I could see the tidally distorted form of NGC 2936 "engulfing" NGC 2937. Observed with a 10mm Delos (205x).

Holmberg I
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With a 26mm UO HD ortho...

With an observing hood, I centered the region without knowing the exact position (only roughly where to look).
Repeatedly observed a patch "above" (NE in this context) a pair of stars and to the right (W) of another star.
Then went back to the DSS and validated the position! Very hard to repeat, extremely faint. Appeared as a somewhat elliptical glow encased on the longer edge of an obtuse angled triangle of three stars.

Changed the eyepiece to 20mm Pentax XW. It was much easier than in the 26mm. Felt like some of those very faint Palomar globulars.

Palomar 1:
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Reached the object after a somewhat elaborate star-hop. Seen with averted vision in 10mm (205x). "Jimi's trick" enhanced the view. Observation confirmed by validating the precise position as determined by observation against DSS image. View was best in 10mm followed by 14mm (147x). Very faint, but confirmed repeatedly; Easier than Fornax Hodge GC 1, though (although they look similar on the DSS, this might be because of airmass. Besides, I was almost an hour and a half past transit for GC 1, whereas I was almost saw Pal 1 on transit.)

Palomar 3:
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Very indistinct glow to one side of a star. Very very faint, harder than Pal 1. Sensed repeatedly at 20mm, 14mm. More difficult than Holmberg I. I must repeat this observation to be absolutely sure, but I am quite convinced. I consistently saw the brightness extend a little more southward than what DSS image (blue plate) suggests -- does anyone corroborate this? (maybe Steve? I hope we end up with one more of those amazing corroborations again :D!)

ACO 1337 a.k.a. "Ursa Major I":
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This is a rather faint Abell cluster within 10 arcminutes of a bright 5.4 mag naked eye star! I learned about this object at TSP 2014 from an astrophotographer.

I observed this object with 10mm Delos (205x). Moving the bright, naked-eye star out of the FOV did help, but was not a must to see one of the brighter galaxies. This galaxy, at RA = 11:47:21 Dec = 55:43:49 (hope I typed that in right), was held continuously with averted vision.

However, most other galaxies popped in and out, giving the feel of a mottled background, much like the case with Abell 2065 (Corona Borealis cluster) through an 18". The galaxies, when they popped into view, however, were more well-defined and stayed for a bit longer, though; i.e. better holding than Abell 2065. This was reminiscent of the fainter galaxies of Abell 2065 through Jimi's telescope, except nowhere as bright. The star needs to be out of the FOV for the fainter members over the western side to pop in and out. It didn't help that I am right-eyed and the star was to the right of the cluster, so I didn't have enough peripheral vision to the right. I missed seeing the BCG (Brightest Cluster Galaxy), as it was too far away and I was unaware that it might be a cluster member.

Clear skies and warm regards,
Akarsh

Very nice. Good targets.

Akarsh,

Great report! Thanks for sharing.

Were these observations made with your 18"?

Great observing report!

Hi Akarsh,

Nice report, great choice of objects. I've viewed all of these at one time or another, but this report has inspired me to revisit them again.

One small observation; I'm pretty sure you were viewing ACO 1377 rather than ACO 1337, which is in Virgo... and 1377 is a LOT better than 1337!

Akarsh, the Fornax Dwarf is nearly overhead Nov-Dec at my lat of 33°S. I've spotted 1049 and Fx 2, 4, & 5 with a Mak MN61 at 174x and Santel 180/1800 at 163-200x. Fx 6 is not a GC but small asterism with a distant galaxy cluster behind it. The GCs are a good test of the night's sky conditions. The dwarf itself is as bright as NGC 6822 in northern skies. See http://www.iceinspace.com.au/63-703-0-0-1-0.html =Dana in SA

Thanks, Preston, Ivan, Dragan, Paul!

Dragan, yes, these observations were with my 18".

Paul, I'm honored that I was able to inspire you. It's almost always the other way around! You are indeed right -- I meant ACO 1377. That was a bad typo (Maybe I was thinking of leetspeak!?).

Dana, thank you for the pointers on Fx 6. So are these the only 5 known / existent globulars in Fornax dwarf? I'm surprised to hear that the Fornax Dwarf is about as bright as NGC 6822 from the south! Amazing. Now all I need is a trip to the south.
Speaking of seeing the dwarf galaxy itself, has anyone seen it from Texas, maybe from Texas Star Party?

Clear Skies!

Regards,
Akarsh

The Fornax GCs are considered as strong evidence for DM. Their orbitals are too distant and high-velocity for the galaxy's visible mass; the DM is thought to be 11 times more massive than the galaxy and to occupy a region 3x the diameter. The Fornax 4 GC's age 4 Gyr younger than the other GCs and peculiarities in Fx4s age-metallicity properties, it is thought to be a capture rather like Ruprecht 106 is thought to be a MW capture. Captured from where is an unsolved question. There was not enough gas or an interaction disturbance to initiate a GC collapse so late in the dwarf's history (about z = 1.5). I hope someday you are able to visit S Africa or Namibia. The skies at my 33° S latitude are dwarf galaxy happy hunting ground. In Oct-Nov one can log Barnard's Gx, IC 5152 Indus, WLM, Sculptor, Fornax, Phoenix, IC 1613, Carina, & the Pegasus Dwarf in a couple of hours. PS: When I said "the Fornax Dwarf is about as bright as NGC 6822" I meant Fornax in a 7" Mak versus 6822 in a 4" refractor.

I really enjoyed your report, Akarsh. As far as Palomar 3, I've only logged it in Jimi's scope and wasn't too precise in described the exact size ---

48" (4/1/11): at 375x, a large, low surface brightness glow was immediately noticed and verified on a Megastar chart, ~2' diameter with an ill-defined periphery. A brighter mag 13.5-14 star is near the southwest end. The glow is very diffuse with just a very weak concentration. With extended viewing, a couple of mottled clumps were visible and a few extremely faint stars were resolved.

Dana, do you have a reference on Fornax 6 being reclassified as a small asterism superimposed on a distant gx cluster? I've looked for it (unsuccessfully) a couple of times, so I was just curious.

Thank you, Steve! I guess your report says that you saw the star on the southwest of the glow. Re-reading my report and looking at the DSS image, I seems to say that I saw the star a little less south-ward than the position of the brightest region on DSS would have led me to think. So it is quite possible that I could be mistaken about this. In any case, I would like to repeat observation of Palomar 3 just to be absolutely sure. Hopefully, I'll get a chance some time soon.

Clear Skies
Akarsh

Quote:

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Originally Posted by Steve Gottlieb

Dana, do you have a reference on Fornax 6 being reclassified as a small asterism superimposed on a distant gx cluster? I've looked for it (unsuccessfully) a couple of times, so I was just curious.

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Hi Steve, pardon the delay, my observing site has no wireless or cell access. I can’t recall the exact paper that mentioned the cluster Fornax 6 is actually an aggregate of field and Fornax dSph red giants with a small remote galaxy group behind it. I believe it’s Buonnono 1998. I have that paper and will look to find the exact phrasing and reference data. It is mentioned under on this NED link. Drop to the “Essential note for Hodge 6” where it reads, “Noted as a compact group of galaxies in 1998PASP..110..533S.”

SIMBAD seems to contradict this, and its data is more recent. If we check Simbad for 02 40 10, -34 26.0 <http://simbad.u-strasbg.fr/simbad/sim-coo?Coord=02+40+10-34+26.0&CooFrame=ICRS&CooEqui=2000.0&CooEpoch=J200 0&Radius=10.0&Radius.unit=arcmin&submit=get+the+li st+of+objects>, within a 10 arcmin radius there are scads of RG, AGB, C, RR and other variables, and plain old * stars, but no galaxies. The red giants listed in Simbad and also in Kirby et al 2010 <1.0 are local field stars, while the Dwarf’s RGs are [Fe/H] -1.71 to -1.35. The SIMBAD AladinLite 8 arcmin viewer for 02 40 07 -34 25 12.6 shows a flat surface brightness profile across the 10 arcmin region, while the DSS and other visual images show what looks like a small compact star cluster. The cluster images are too stellar to match a remote galaxy’s surface profile, which argues against a galaxy cluster any brighter than 23.5. This may be because the AladinLite viewer does not segregate by B–V or R–I the way most photometry equipment does. The SIMBAD entry “Name cluster 6 in Fornax” refers 6 reference papers, all of them pretty old. The Buononno 1998 paper is a pretty good read, galaxy cluster or not.

Attachment 1523
http://ned.ipac.caltech.edu/dss/HODGE_6.gif
NED image for 2’ field at Hodge 6 position.

Thanks for the infomration, Dana. Here's the relevant paragraphs in the 1998 PASP paper referenced in NED --

In his early discussion of the globular clusters in Fornax, Shapley (1939) identified a faint object lying some 7' north of globular cluster 4 as a possible additional cluster belonging to the galaxy. Hodge (1961a) described it as a group of five stars of approximately 21st magnitude; the implication was that he regarded its reality as a cluster to be dubious. As recently as 1994, Demers et al. considered the existence of the cluster as still worthy of debate, but stated that in their opinion the region contained "too few stars to be called a cluster."

The asterism known as cluster 6 was contained within nine of our frame pairs, and the depth and dynamic range of our stacked image allows us to contribute a new (as far as we can tell) observation to the discussion: nearly half of the “stars” in cluster 6 appear to us to be nonstellar and seem to constitute a very faint compact group of galaxies. In particular, utilizing the numbering scheme of Verner et al. (1981), objects 13, 19, 25, 39, 40, and 41 appear to be distinctly nonstellar in form. Several of the other, unnumbered objects in the area also appear to be nonstellar, such as an object 2" to the east of “star” 39, another 3" to the northeast of 39 (the western object of a 1" pair), an object 4" to the west of star 44, and a pair of objects 2" north‐northeast of 13. The degree of resolution of these objects is very slight, and it takes some playing with the brightness and contrast controls of the image display to convince oneself that their surface brightness is somewhat too low for their integrated fluxes, in comparison to nearby stars of similar apparent magnitude. There appear to be some other faint objects that cluster in this region, but they are so near the detection limit that we cannot judge which might be stars and which galaxies. We therefore conclude that at least part of "cluster 6" might still be worthy of further investigation, but as a very distant compact group of galaxies rather than as a star cluster.

Wow. The "asterism superposed on a distant galaxy cluster" thing is mindblowing! I wish it was within amateur reach. Thanks for this discussion Dana, Steve.

BTW, I compiled a report on the Fornax GCs for the Austin Astro. Soc. newsletter, because I found that it was harder than usual for me to find amateur reports on the internet on this set of objects (Steve, did you ever have a report on Adventures in Deep Space on this set? I see you mention it in the extragalactic GCs page). Here is an unrefined, but internet-searchable version: http://bas.org.in/~akarsh/Fornax_Hodge_GCs_report.html
It is written with the flavor of reaching out to beginning visual observers as well, hence the introductory discussion on other extragalactic GCs. I would welcome everyone's comments on this article, particularly since it is my first.

With your permissions, Dana and Steve, I would like to include in this article, excerpts of the story on "cluster 6" and also, a link to Dana's very detailed article on CN (which I am yet to read), so that anyone stumbling upon the article knows some details on where to look for more information.

Thank you.

Regards
Akarsh