Wednesday, September 4, 2013

Colliding Galaxies and Exploding Stars

While the summer weather along the Gulf Coast is usually bad for observing deep sky objects, last week conditions improved enough to make it worthwhile to drive to a darker site than my driveway. Before that a rare occurrence became visible to the unaided eye, a classical nova in the constellation Delphinus bright enough to be seen from a suburban area from the northern hemisphere. Two supernovae in nearby galaxies are also now visible to amateurs with modest telescopes from a reasonably dark site. And while Saturn edges ever nearer to the Sun, Venus, Jupiter and Mars are moving away from it into a good position to be observed from Earth. Uranus and Neptune are already well placed for observation as Comet C/2012S1 ISON continues it's approach towards the Sun ahead of perihelion in November of this year.
Nova Delphini 2013 burst onto the scene over two weeks ago, reaching fourth magnitude in less than two days. The system where the nova outburst originated normally is at 17th magnitude at best, giving this nova outburst a luminosity of at least 100,000 Suns from it's location some 10,000 light years away. It's rapid rise to peak brightness at first seemed to indicate this is a "fast nova," one that reaches maximum brightness rapidly then fades rapidly from view, but it is apparent that is not what this nova is. It is still at 7th magnitude and is fading relatively slowly, reddening as it dims. Located near the planetary nebula NGC-6905, my 10-inch showed both the nova and the nebula easily through my 10-inch with a 24mm ES 82 degree eyepiece. Through the 15-inch and the same eyepiece, both will still fit in the same field of view because the nova and nebula are about 45 arc-minutes apart. It appears to be a slow nova, which often fade, then brighten a second or even a third time before they finally begin returning to their normal state as a faint, very dense white hot star. Because there has been no outbursts from this star recorded previously, this is a classical nova that will not erupt again possibly for thousands or tens of thousands of years. Due to it's immense distance from the Sun, we are seeing an explosion that occurred some10,000 years ago. Click on the link below for more information on this nova. At any rate, this is an opportunity for amateurs to follow a bright nova as it returns to normal. When I first sighted it, the nova was a yellowish white in color, but by the time this drawing was made the yellow tint deepened. As it fades, it color will become more reddish due to strong emissions from ionized hydrogen.

Nova Delphini 2013 is not the only exploding star visible to amateur astronomers at the same time. In nearby Lacerta is the galaxy NGC-7250 where a former nova destroyed itself as a type 1A supernova designated as SN2013dy. Unlike Nova Delphini, this white dwarf accumulated so much matter from another star it could no longer support itself against its own gravity. It collapsed and a thermonuclear runaway started, consuming the entire star in seconds and blowing it apart. Normally NGC-7250 is of little interest, it is very small and clearly irregular through the 15-inch, but the supernova was obvious at one end of this elongated galaxy. I would say right now it has an apparent magnitude of about 14, it took verification with a higher power eyepiece and a finder chart to see that yes indeed I had found SN2013dy. It can be seen with an 10 or 12-inch telescope under a reasonably dark sky, even and 8-inch might reveal it. Unfortunately, cloudy weather prevented me from seeing it at peak brightness, I was only able to catch this one well into it's decline. Also visible is another type 1A supernova in the Pisces galaxy M-74, but I was not able to find the galaxy before the moon drowned it out. The supernova will however remain visible for quite some time because the galaxy is close to ours, giving amatuers more time to find it. Currently it's at mangitude 12.6, visible to a small telescope in the outskirts of M-74.
Draco hosts a large number of galaxies, most of them faint or very faint. NGC-5908 is not a particularly bright object, but it does have a high surface brightness and shows up readily in less than perfect skies. Shining at magnitude 11.9 and with an apparent size of 3 arc-minutes, this object shows a spindle like outline and a rapid brightening towards the center. This galaxy is oriented nearly north-south and is a spiral of type Sb, similar to Andromeda. It also makes a pair with the 12th magnitude barred spiral galaxy NGC-5905, which I did not see that night. Sky conditions were quite poor, it was possible I was looking right at it and missed it. This pair will be the subject of a repeat visit, and the bright galaxies M-102 and NGC-5907 lie nearby. In all, this region of sky offers one face-on barred spiral, two edge on spiral galaxies and a lenticular galaxy.
Also in Draco is the galaxy duo NGC-5963 and 5965, the brightest two members of a quartet of galaxies. Unfortunately I did not find the other two members NGC-5971 and 5969, both of which are near 15th magnitude. The sky conditions were simply too bright and milky for them to be visible, but I am sure they can be seen from a very dark area when the skies are clear and moonless. In contrast to the very small apparent size and extreme faintness of the other pair, NGG-5963 and 5965 are brighter and easy to see. They hardly need a 15-inch, indeed an 8-inch under good conditions will show them well from a good site. NGC-5963 is a 12th magnitude Sc spiral galaxy that is inclined, giving it an oval shape with a brighter center that is 3.3 arc-minutes long. NGC-5965 is an edge on Sb spiral galaxy with a bright nuclear bulge and hints of it's spiral structure evident at 227X. One edge of the nuclear bulge was sharp and straight, hinting at the dust lane most spiral galaxies have. It was subtly patchy and so was NGC-5963. NGC-5965 has a total magnitude of 12.6 and an apparent size of .7 X 5.2 arc-minutes, making it a flat galaxy.
Yet another rich hunting ground for galaxies is the constellation Serpens Caput. One of the better finds for modest telescopes under good skies are the merging galaxies NGC-5953 and 5954. While NGC-5953 is an oval SAp galaxy, NGC-5954 is a severely distorted star burst galaxy that resembles a seedpod in shape. NGC-5953 apparent size is 1.3 X 1.6 arc-minutes with a strong brightening towards the center. Overall the galaxy shines with a magnitude of 12. NGC-5954 has an apparent size of 1.3 by .6 arc-minutes and is pointing nearly due north-south on the sky, with an total magnitude of 11.6. Intense bursts of star formation are underway in this SAB peculiar galaxy with an evident bridge between the two visible in photos. The nuclear region is clearly displaced towards one end of NGG-5954. Visually I saw that the halos of one galaxy merged into the other's. Eventually these colliding galaxies will merge into a larger elliptical galaxy. Located nearby and visible in a low power eyepiece is the edge on galaxy NGC-5951. It is a very flat, faint galaxy I failed to find under the rather poor skies that night, but under good conditions it will appear with the other two galaxies through an 8 or 10-inch telescope. At 13th magnitude with an length of 3.5 arc-minutes, this galaxy is very ghostly due to a low surface brightness.That is why NGC-5951 is evidently quite inconspicuous, and worthy of another visit to the region when Serpens is in a favorable position for observation again. At present twilight will soon engulf Serpens, making observations of it's galaxies impossible until winter before dawn.
NGC-5962 is a rather faint oval galaxy with a weak central brightening. Shining at magnitude 11.7 and spanning 3 X 2.1 arc-minutes of sky, this Sc spiral does not show a prominent central core but does look slightly patchy in keeping with it's classification as a loose spiral galaxy. It did however stand up to high magnification well, a 6.7mm eyepiece yielded 298X which offered a nice view of this galaxy.
NGC-5970 is another Serpens galaxy visible in modest telescopes, indeed I have bagged this one with a 6-inch from the same site where I sketched it with my 15-inch. Like NGC-6962, this galaxy is also a spiral system but it is a barred spiral galaxy of type SBc with it's long axis aligned almost exactly due east to west. A little brighter at magnitude 11.4 and spanning 2.9 X 1.9 arc-minutes this oval galaxy also has a stronger central brightening than NGC-5962, and it too is also patchy. In photos it's outer spiral arms resemble those of M-63, the Sunflower Galaxy.
These drawings were made over two consecutive nights, but the objects shown here are not the only ones I paid a visit to. Other objects I visited are the globular clusters M-5, M-9, M-22, M-13, M-15, M-57, NGC-6723, and NCG-7006. I spent time examining the open clusters M-11, NGC-6520 and it's dark nebula Barnard 86, and NGC-6939. Other galaxies I observed but did not sketch were the Andromeda and Triangulum galaxies as well as Local Group members NGC-147, NGC-185, M-32 and M-110. The Cassiopeia galaxy NGC-278 and the Cepheus galaxy NGC-6946 were also observed. Other galaxies observed were Stephan's Quintet, NGC-7331 and NGC-7769 and 7771 in Pegasus. Finally I stopped to explore all three main sections of the Veil Nebula, which looked like a bridal veil through the 24mm Explore Scientific 82 degree eyepiece and an O-III filter. The North American nebula showed streaks and patches of dark and bright nebulosity, and I traced the full outline of NGC-6888, the Crescent Nebula and NGC-281, the Pac Man nebula. I also gazed upon the Lagoon, Triffid, Eagle and Omega nebulae. I also observed scores of planetary nebulae, including NGC-6905, 6826, NGC-40, and M-57 and M-27. I was happy to be able to observe from a spot darker than my driveway, and to see objects that are impossible to see at home, even with a 15-inch.