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Comet PanStarrs, 3 (4?) SN and a globular in M33

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#1 timokarhula


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Posted 13 September 2013 - 04:29 AM

The other night, I observed with my local astronomy club's, VARF, brand new 16-inch Orion Optics Optimized Dall-Kirkham telescope on a 10 Micron GM2000 HPS mount. I used almost exclusively 300x magnification (9mm Nagler). The seeing was crummy in the beginning of the session when I looked at Uranus. The planet was flickering and only the moon Titania was seen occasionally. The visual magnitudes below are from APASS, if not otherwise noted.

Comet C/2011 L4 (PanStarrs), which was a naked eye object half a year ago, was still visible telescopically. It was located in Bootes and seemed fainter than 14th magnitude and about 0'.7 in diameter.

NGC2748 in Camelopardalis is a very elongated galaxy. Here I glimpsed the supernova SN2013ff. I estimated it as magnitude 15.6. Noted several stars not plotted on my MegaStar chart. The dimmest of them, a star near the galaxy's northern tip, proved to be of V=16.03.

I had seen SN2013dy in NGC7250 (Lacerta) a month ago. The supernova had faded to magnitude 15.1. I happened to note a field star of V-magnitude 16.15 not plotted on my chart.

The supernova SN2013ej in M74 had also dimmed during the last month. Estimated SN2013ej as magnitude 13.3. Very easy to see.

UGC5609 is a faint galaxy in Draco. The supernova SN2013eu is situated just 3" W and 9" S of the galaxy's centre. I occasionally glimpsed a stellar object here. It was fainter than a 15.7 magnitude star, but I don't know whether this was SN2013eu or just the nucleus of UGC5609. I observed three, or maybe four, supernovae in just more than one hour!

The field was interesting with the neighbour, UGC5600, just 1'.3 NW of it. They were similar, had a low surface brightness but UGC5600 contained a brighter stellar centre. The magnitude 15.9 galaxy MCG+13-8-18 was nearby. A fourth galaxy, 7ZW 319 (PGC30266), was indeed also visible. Its magnitude is 16.3 according to NED and the size is 0'.6x0'.4. I could discern its non-stellar character. It must have been the first time I observed an anonymous galaxy in the 7ZW-catalog! These are compact galaxies catalogued by Fritz Zwicky.

When I analyzed my observations, I noted that one of my field stars that I had ringed in was not actually a star but an anonymous galaxy, 2MASX J10203816+7841014! The B-magnitude is 15.9 according to NED but it does not give the size. On the Digitized Sky Survey it looks somewhat bigger than 7ZW 319. The reason why these galaxies can be seen with only 16-inch aperture are their small size and high surface brightness. There were more galaxies in the field of view.

The last object for the night was M33, the Triangulum galaxy. I star-hopped from the large emission nebula NGC604 towards south (here I saw some mottling in the cloud, have to return to it!). Here would the galaxy's brightest globular cluster, C39, reside. After some concentration, I could glimpse the V-magnitude 15.9 globular above my city Västerås' light dome. The cluster was stellar, difficult but definitive. C39 is the most remote globular that I have seen, distance about 3 million light-years. It's half a million light-years more distant than the easier globular clusters in the Andromeda galaxy.

I measured the darkness of the sky with my SQM-L device. From here, 7 km north of Västerås centre (population 140,000), it was 20.6 magnitudes per square arc-second. Towards the north, it was a little bit darker, 20.9. I could glimpse a V-magnitude 16.6 star near the Ring nebula last week with the 16-inch from here. It is still a much brighter sky than my regular observing site 40 km from here. It was a joy using the new ODK-telescope.

/Timo Karhula

#2 IVM



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Posted 13 September 2013 - 07:37 AM

Fine observation of C39. I attempted it with my 12" SCT once.

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