Sunday, April 6, 2014

Winter and spring deep sky objects

Winter has finally drawn to a close and with the departure of the cold comes hordes of galaxies as soon as it becomes completely dark. Nevertheless, some winter objects remain in view and therefore I observed a few of them before they are lost in the glare of the Sun. Along with the arrival of warmer temperatures nights are getting shorter and all of the major planets are visible now at some point during the night. It is still stormy and murky most of the time, but a few good nights have come along, good enough to make taking the 15-inch to a darker skies worth the effort. The drawings shown here were made over a two week period last month. 
The Ursa Major galaxy M-82 is one of my favorite galaxies, but recently a bright Type 1A supernova has appeared there. I have been following it ever since I learned of it's eruption. Reaching a peak brightness of about magnitude 10, it was unmistakably visible even at home despite the heavy light pollution. Here in this drawing the supernova was shining at about magnitude 11.7 as it fades towards invisibility. The last time I examined M-82 the supernova was still visible, but now it's too faint to still see from my house at a magnitude of 12.9. If you wish to see this supernova, look for it now because soon it will be out of range of all but very large professional telescopes and those equipped with ultra-sensitive cameras. It is quite a thrill to witness an event that actually happened 12 million years ago.
 The southerly constellation Columba the Dove is poorly seen if not invisible from the U.S. and Europe, but contains both Milky Way and extra-galactic objects within it's confines. The brightest and best of these objects is the bright, small and concentrated globular cluster NGC-1851. It can be seen in small telescopes as a small, round, fairly bright object that resembles a comet with an intense inner core. It's hindered by the low elevation in my local skies, but through my 15-inch it breaks up into stars, resembling a southern version of the Pegasus globular cluster, M-15.
Auriga has many, many open clusters, nebulae and even a globular cluster in it's borders. One such object I have always been interested in is the open cluster NGC-1893 and the emission nebula that surrounds it, IC-410. The sky conditions at the time were quite poor, but when I put a narrow band nebula filter on the eyepiece regions of faint nebulosity appeared. The most prominent was a ring like patch with a darker center and spangled with stars.
While Orion is well known for the Messier objects M-42, M-42 and M-78, it has dozens of less well known objects that are worthy of study. One object I wanted to make the acquaintance of was the ninth magnitude open cluster NGC-2112. Fairly small and perhaps consisting of two dozen stars, it is an inconspicuous object amid the dense star fields and hordes of brighter nebulae and star clusters. It spans 11 arc-minutes and required 227X to distinguish from the surrounding star field.
The bright, rich and large open cluster M-35 is undeniably one of the finest object in the winter sky, and I have observed it many times over the years. It does however share the field of view with a much more massive and distant open cluster that is six times farther away from us than M-35. That star cluster lies some 2,800 light years away. It's some 100 million years old, and had a total population of at least 500 stars across an area about 25 light years across. NGC-2158 normally appears as a small fuzzy comet like spot some 15 arc-minutes away from the center of M-35 and lies at the enormous distance of at least 16,000 light years. To my amazement, it showed partial resolution into stars at my house on a good night, and resolved into a swarm of very faint stars at the club's darker sky site. This star cluster has an age of some 800 million years, the brightest Main Sequence stars having a spectral type of F0. Shining at magnitude 8.6 and an apparent size of 5 arc-minutes, NGC-2158 is worthy of close scrutiny for those with larger telescopes, and makes a nice showing together with M-35 in smaller instruments.
NGC-2420 is another ancient open cluster in Gemini, with a total population of at least 1,000 stars and an age of 1.7 billion years. It is also 3,000 light years from the plane of the Milky Way's disk and is 30 light years across. It's right now some 33,000 light years from the center of the Milky Way, placing it some 8,000 light years away from Earth. Shining at magnitude 8.3 and spanning 10 arc-minutes of sky, this massive and aged open cluster curiously has the same chemical composition of our Sun and Solar System. It readily resolved into stars through the 15-inch despite the rather bad skies that night, and doubtlessly would reveal it's nature to users of 8 and 10-inch telescopes under good skies at dark sites. Most open clusters disintegrate under the relentless gravitational forces of the Milky Way's disk, but NGC-2420's orbit around the galactic center and it's high mass enabled it to hold onto at least 1,000 of it's original compliment of stars. Many red-giant and helium burning stars exist in the star cluster, along with white dwarfs.
As winter gives way to spring, Ursa Major and it's swarms of galaxies near and far rise high into the sky as night falls. The entire constellation is riddled with every type and size of galaxy imaginable, so I opted to concentrate on the brighter ones in Ursa Major's head. NGC-2742 is fairly faint and large, with an obvious nuclear region and a slightly wooly halo at 181X. It is a spiral galaxy of type SC shining at magnitude 11.7 with an apparent size of 3 X 1.5 arc-minutes. It's oval outline is oriented almost exactly east to west. Overall, a nice example of a type-Sc spiral galaxy whose inclination is between face and edge-on. The galaxy NGC-2768 lies 40 arc-minutes away to the southeast.
NGC-2768 is another fairly bright Ursa Major galaxy I have observed before with smaller telescopes. This tenth magnitude object is 8. X 4.3 arc-minutes long and has a bright central core. Unlike NGC-2742 which is forming stars, this galaxy is a lenticular or disk shaped system dominated by old yellow and red stars. It is lacking in interstellar dust and gas from which new stars form, as a consequence it appears more featureless than it's neighbor through the telescope. It also has nearly the same orientation in the sky as NGC-2742.
NGC-2787 is a barred spiral galaxy shining at magnitude 10.9 and has an apparent size of 3 X 2 arc-minutes. This SB-O galaxy was small, oval and had a bright core, though I did not plainly see the central bar at 227X. I had a difficult time determining which way the galaxy was oriented as I made this sketch, perhaps because the bar is nearly at right angles to the rest of NGC-2787's featureless disk.
NGC-2810 is a small elliptical galaxy with a bright center but otherwise it appears as a featureless, circular glow. Shining at magnitude 12.3 and being only two arc-minutes across, this galaxy is one of the less impressive systems in Ursa Major at 227X. I had thought I glimpsed a star like nucleus in this galaxy, but its faintness and small apparent size is due to small size and or lying at an immense distance from Earth.
NGC-2880 is brighter than NGC-2810, shining at magnitude 11.6 and spanning 2 X 1.2 arc-minutes of sky. Like NGC-2768 however, this is a lenticular galaxy of Hubble classification SB-O. It shows it's oval outline and a brighter center, but is otherwise featureless due to the absence of spiral arms or star formation. It does however respond well to higher magnifications and stands out better against the sky due to the much higher surface brightness than NGC-2810.
NGC-2950 is an eleventh magnitude object that spans three arc-minutes in length. It lies next to a convenient guide star for those who star hop to objects. It is either a lenticular or a transitional system between a barred spiral and a lenticular galaxy. What appeared in the 15-inch at 227X was a fairly bright, oval object with a very bright central core. The halo around it was much fainter and the object's small apparent size enabled it to show up well through the worsening skies. Soon after observing this galaxy, it was clear the skies were about to give out. So I observed a few more objects, then took down and packed away the telescope for the trip home.

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