Roaming the Deep Sky #13
NGC4449
By Don Clouse
One of the neat things about doing an observing list is encountering the unexpected. Over the past few months, I’ve been concentrating on galaxies that are on the Herschel 400 observing list. This state of affairs has arisen quite naturally since the earth’s nighttime skies in the spring direct our gaze out of the plane of the Milky Way and into intergalactic space. Of course, the fact that a majority of the objects on the list are galaxies is a big factor too. Now, I’ve come to expect that what I’ll usually see when I look at a "Herschel" galaxy in my 8" telescope is a fairly small and faint object with some amount of variation in detail from one object to the next, but really, basically unremarkable. (Not that I don’t enjoy finding and viewing them too. The hunt itself is rewarding.) Now and then, though, you get surprised. HCG44, described in last month’s article, was one such. Another very nice surprise occurred on the night of May 12, 2001 while observing at "the Farm" (Pat Peak’s brother’s place south of Shepherdsville) with LAA. Actually, there were three nice surprises on this particular observing run. However, since these articles are supposed to be about a single field of view, I’ll forego the temptation to expound upon all three and skip directly to the main attraction – NGC4449.
NGC4449 is located about 12 million light years away in the Canes Venatici galaxy group. This galaxy is a Magellanic dwarf. Its structure and size is quite similar to that of the Large Magellanic Cloud. The long central axis of the galaxy consists of a bar of young stars less than five million years old. The bright spots that are visible in an amateur telescope are giant H II regions where bursts of star formation have occurred. The radiation from the hot, massive newborn stars ionizes the surrounding gases (mostly hydrogen) which, in turn, reradiate the energy in the form of light. These knots of star formation are no doubt, quite similar to the Tarantula Nebula, or 30 Doradus, in the Large Magellanic Cloud.
I’m sure that seasoned observers are quite familiar with this galaxy. However, it was a total surprise to me. What I was struck by was how bright NGC4449 is and the amount of detail that could be seen in only an eight-inch telescope. Observing with my Celestron 8" SCT with a 30’ field of view at 135x (15mm Panoptic), it had a distinctly rectangular shape with two or three bright spots arrayed along the long axis. Larger aperture telescopes will show even more detail including further star forming regions, a dark lane or spot, and additional structure in the outer "envelope". I estimated its size at about 4’x2’. NGC4449’s size is catalogued at anywhere from 4.6’ x 3.2’ (MegaStar 4.0, E.L.B. Software, Willman-Bell, Inc., 1996) to 5.5’ x 4.1’ (The Night Sky Observer’s Guide, Kepple and Sanner, Willman-Bell, Inc., 1998, http://www.willbell.com/). Its magnitude is listed from 9.4 to 10.0. This galaxy’s location on the sky in Canes Venatici is shown in the chart. Beta Canum Venaticorum is shown in the lower left corner. NGC4449 is near the upper middle. Several additional galaxies, to 15th magnitude, are shown. The magnitude, without a decimal in tenths place, is appended to the galaxies’ names. Stars are shown to 11th magnitude. The chart spans 6.4 degrees by 4.0 degrees.
I find it fairly remarkable that our amateur telescopes will show us star forming regions in other galaxies. NGC4449 was quite an unexpected treat. It inspires me to tackle yet another "project", namely, trying to identify star forming regions in other nearby galaxies such as M31 (surprisingly with only one NGC nebula/"knot"), M101 (three NGC’s), and M33 (two NGC’s and 8 IC’s!). I wonder how many others there are? How many are visible in an 8" scope or a 16" scope? Canes Venatici and NGC4449 (declination +44 degrees) owing to their high declination are visible sometime during the night much of the year. However, NGC4449 is best placed from mid-winter through early summer. The next time you’re "arcing to Arcturus" stop at the end of the Big Dipper’s handle and take a left to NGC4449. Happy hunting.
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