A supernova discovered (almost)

Each new moon weekend a group of amateur astronomers from the Sutherland Astronomical Society head to a dark site at Bargo outside Sydney to do some serious observing. Last Saturday (24 June) Les Dalrymple thought that he had discovered an exploding star or supernova. Here is his tale:

And then consternation struck with the next galaxy …

NGC 5612 Galaxy *
RA: 14h 34m 02.0s Dec: -78° 23′ 16″
Mag: 13.0 (B) S.B.: 11.9 B-V: +0.93
Size: 1.8’x0.9′ Class: SAab: P.A.: 58
Inclination: — R.V.: +2699

x185 27′ TF
x247 20′ TF

On the DSS this appears as a pretty unremarkable early type spiral or perhaps S type eg. Immediately with the 12mm type II it seems to have a second condensation or stellaring in the SW end of the halo, 1/2 way out in the halo just south of the axis. This is _not_ shown on real sky (but was later found to be shown clearly as a star in the POSS 2nd gen red plate). It is more nearly *ar with the 7mm at x317. Overall it would seem 1.25′ x 40″ in PA 45, with an oval/lens shaped outline with a slight, broad concentration to the centre without zones or nucleus. The star seems to be at about mag 15, but is difficult to estimate accurately as it is superimposed on the halo.

Initially of course when I saw that star in the SW end of the halo and more particularly when I saw it _wasn’t_ in the DSS image provided by realsky my heart was set pitter-pattering. Gary and the two Jeffs all confirmed the existence of the star and it’s position was carefully noted so I could investigate it the following morning. I even attempted to call Rob McNaught at Siding Spring to perhaps image it, but got no answer (it was his home number — not the number in the dome).

The next morning on the net I called up the POSS image (a 2nd gen UKS red image) on STScI:

POSS image of supernova NGC 5612

and surprisingly — there was the star — right where I had recorded it. Couldn’t believe it! Looked at it real sky again and lo and behold — not there. Hmmm … How can it be on the 2nd gen survey image and not on the first gen image. Couldn’t be a supernova it would have faded between the 2nd gen image and now. Hmmm … I did some digging around on SIMBAD and Aladdin which turned up almost nothing. There had been a relatively recent supernova in NGC5612 — 2004 CH but that was over the other side of the halo and not where my star was. Hmmm … Maybe it is a previously unknown variable; A RCB star?? So I figured I’d better ask an expert and posted it on AMASTRO where I knew someone with better investigative skills would hopefully be able to explain it.

Within a 1/2 hour Brian Skiff and Lowell observatory had done the research. Here is his extracted reply to my post:

The superposed star is reasonably well catalogued, including in UCAC2 at position: 14 33 56.78 -78 23 27.9 (J2000), with uncertainty well under 0″.1. The 2MASS J-K color (~0.6) is that of an ordinary K0 giant if correct. Could also be a mid-K dwarf, which is not unreasonable given the modest proper motion shown in UCAC2. (The motion, however, may result from some skewness in older positions caused by the galaxy.) Making the giant assumption, the DENIS I-band magnitude (~13.7) implies a V magnitude close to 15.0, perhaps a few tenths brighter. Again, there might be problems with being superposed on the galaxy.

In NED, there is a note about the star copied from the RC1 (1964). This would have resulted from examination of a Mount Stromlo 30-inch (Reynolds?) reflector plate taken in the 1950s when de Vaucouleurs was down there. This and the ordinary appearance on the various sky survey plates suggests there is nothing odd about the star. I observed the galaxy in 1990 on my first Chile trip with a 15cm refractor. I didn’t mention the star—probably just a bit too faint— but noted that the core region was narrow and extended, so perhaps the star added a bit to what might have been seen otherwise. Overall I described the galaxy as moderately faint but of moderately high surface brightness.

…Les also was worried about the problematic appearance on the ‘RealSky’ images. This is almost certainly from 100x compression of the data, and this is just the sort of thing where it matters. Since better data is available now on the Web, just ignore it.

Brian

So, it turns out to be just a plain old K type giant. Oh well.
Les Dalrymple

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