Observing Report: The five globular clusters in the Fornax dwarf galaxy

Note: A version of this article appeared in the Austin Astronomical Society's monthly newsletter, the Sidereal Times in February 2015. Here is a link to the full newsletter. The beautiful typesetting is the work of our Newsletter Editor Joyce Lynch.

I was lucky to catch some photons during this January's new moon period! Fortunately for me, I had no obligations on the 19^th and 20^th of January, so I decided to go observing on the 19^th despite it being a Monday, after ensuring that multiple weather sources predicted a very clear night...

And a clear night it was! The sunset was at 6 PM, but it was about 6:40 by the time I pulled in under slowly darkening Bortle 2 skies near Pontotoc, TX. It was only by 8:30 PM that I had my Obsession 18” f/4.5 fully set up and ready to observe. The sky conditions were excellent. The milky way in Cassiopeia was shining surprisingly bright. Zodiacal light was extremely bright after sunset, and it was still lingering at 8:30 PM! I didn't look very carefully for the Gegenschein, but I noticed that the milky way near Orion had an unusual bulge, which was probably due to the Gegenschein. Sky conditions stayed great all night, so I got a lot of observing done.

There were a few personal highlights to the session, and very many interesting objects, but I shall not belabor on the details, and shall instead focus on an interesting set of targets that I pursued, which seem less popular than I feel they ought to be – and these are the five globular clusters in the Fornax dwarf galaxy.

Wait a minute, globulars in another galaxy? Yes. If you've finished the Messier catalog, you have already seen a globular cluster in another galaxy – and that is M 54. It's visible even with binoculars! This globular cluster is believed to belong to the Sagittarius Dwarf Elliptical Galaxy (SagDEG), a satellite galaxy of the Milky Way. With the large apertures available these days, objects in our more distant galactic neighbors are not uncommon targets for amateurs either. For example, the nebula NGC 604 in M33, and globular cluster Mayall II in M 31, are quite popular.

The Fornax dwarf galaxy is a satellite of the Milky Way, lying in the direction of the constellation of Fornax. Although the galaxy itself was first discovered by Harlow Shapley in 1938¹, the brightest of the five globular clusters in it, NGC 1049, was discovered much earlier in 1835 by Sir John Herschel². Shortly after the discovery of the dwarf, in 1939, Shapley identified two globular clusters superposed on it³. Thereafter, Paul Hodge⁴ identified two more globulars in the dwarf (1961).

Here in central Texas, the galaxy rises no more than a mere 25 degrees above the southern horizon. This makes the galaxy itself a difficult target, owing to its low surface brightness. The low southern declination might in fact be the cause of the low popularity of these targets – it is even more difficult for most of the USA and Canada. However, the tiny globulars are indeed quite tractable from Texas. While I may have detected hints of the galaxy's glow, I definitely cannot be certain about having seen the galaxy; the globulars, I did see, and I shall focus on them.

Paul Hodge's “An Atlas of Local Group Galaxies”, which I checked out from the UT Library, is a great reference for anyone hunting extragalactic objects. It lists the 5 globulars and also a planetary nebula in the Fornax dwarf. However, the book by itself is not readily usable on the field, so I prepared in advance by feeding the coordinates into the astronomy software KStars⁵, and subsequently downloading the imagery from the Digitized Sky Survey. This preparation helped me immensely on the field, as for the fainter globulars, precise positioning was essential.

NGC 1049 (GC 3 in Hodge's 1961 paper):

Although the Fornax system transited meridian at around 7:50 PM that night, owing to my late start, it was not until an hour later that I managed to grab NGC 1049. I had seen NGC 1049 earlier with a 17.5” from a dark sky site in the hills of south-western India, so this wasn't a daunting target. At 66x, the object appeared virtually like a star. At 103x, it started appearing non-stellar, but still, it wasn't distinctly non-stellar. I could tell it looked different from other stars because it had a bit more of a halo around it. Putting on a 10mm eyepiece (205x), it finally was distinctly non-stellar. This was the easiest and brightest of the 5 globulars.

Hodge's GC 4:

This was the second easiest of the five. It was quite clearly detected in my field of view when I moved towards the bright star near the globular. It felt just a tad more condensed than NGC 1049, if at all, but was otherwise similar. It appeared distinctly non-stellar at 205x.

Hodge's GC 2:

GC 2 was more diffuse than GC4 and NGC 1049. It appeared as a uniform glow at 205x. Was not at all as obvious as GC4 or NGC 1049. It took me about 10 seconds of staring to realize that it was present in the field of view. I would rate this as the 4^th easiest globular, after GC 5.

Hodge's GC 5:

GC 5 is quite reminiscent of GC 4, condensed and of nearly equal brightness. Detected with a 10mm eyepiece (205x). I would rank it 3^rd in ease of observing, after GC 2 and before GC4.

Hodge's GC 1:

This was the most difficult of the 5 globulars. Also, by this time, it was already 9:30 PM, so a bit more than an hour and a half after transit. The object was at the very edge of visibility! I sensed it a multiple number of times, with the object popping in and out of the sky background. A trick that I learned from Jimi Lowrey, of rocking the focus in and out to detect faint objects, really helped. I knew almost exactly where to look, but the even-more-precise position was noted by observation and then verified against images. The size of the very, very, faint glow was comparable, if not larger than GC 2. I had the best view using a Pentax 14mm XS (147x). A 16mm Orthoscopic (128x) costing $50 was also able to give a very good view.

For the reference of anyone who might be interested in trying these objects, I provide here the coordinates of these five globulars as obtained from the SIMBAD⁶ database:

Name	RA (J2000)	Dec (J2000)
GC 1	02:37:02.1	-34:11:00
GC 2	02:38:40.1	-34:48:05
NGC 1049 (GC 3)	02:39:48.3	-34:15:28
GC 4	02:40:07.7	-34:32:11
GC 5	02:42:21.1	-34:06:06
Fornax Dwarf Gxy	02:39:59.3	-34:26:57

Overall, I had a very productive and enjoyable observing session. I'd like to use this opportunity to thank AAS member Greg for permitting me to observe from his grounds, and also my family for supporting my astronomy interests – something that my student stipend cannot afford.

I would also like to thank Steve Gottlieb and others for Adventures in Deep Space, which is where I got to know of most of my targets from.