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2020leu - Supernova in NGC 5363

PostPosted: Sat May 30, 2020 4:30 am
by Peter Velez
Managed to image 2 supernovae last night.

2020leu was reported on 27 May 2020 and observed on 24 May. It appears to be in NGC 5363 which has a reported redshift of 0.0037. No spectra are available as yet and it hasn't been classified either.

Here is a spectrum taken from 21 x 300 s images binned x2 through a LISA using a 23 micron slit (again, likely undersampled - one of the joys of imaging remotely is its not so easy to change the slit or tweak the focus). Taken with an ATIK 460EX mounted on a PW CDK 12.5 from the iTelescope facility at Siding Springs Observatory.

Gelato suggests this is a Type II SN but its an unreliable classification - given how noisy the spectrum is, that is not surprising. This target is reasonably well positioned for me to devote several hours to it so, weather permitting, I'll have another go this evening.

Pete

Re: 2020leu - Supernova in NGC 5363

PostPosted: Sat May 30, 2020 12:27 pm
by Robin Leadbeater
Hi Peter,

That looks like the galaxy spectrum to me. Try overlaying a typical mid K type spectrum over it

Cheers
Robin

Re: 2020leu - Supernova in NGC 5363

PostPosted: Sat May 30, 2020 12:35 pm
by Robin Leadbeater
I see in TNS the coordinates are wrong but from the description given, Stan Howerton in his note added 20200527 believes it corresponds to a known foreground star.
https://wis-tns.weizmann.ac.il/object/2020leu
Assuming you were on the star and not the galaxy background, your spectrum confirms it is a foreground K type star and not a supernova. You could do an approximate classification of the star

Cheers
Robin

Re: 2020leu - Supernova in NGC 5363

PostPosted: Sat May 30, 2020 12:37 pm
by Peter Velez
Robin Leadbeater wrote:Hi Peter,

That looks like the galaxy spectrum to me. Try overlaying a typical mid K type spectrum over it

Cheers
Robin


I fear you may be correct Robin

I'm plugging away on it again this evening - will process it in the am and see what I get.

Pete

Re: 2020leu - Supernova in NGC 5363

PostPosted: Sat May 30, 2020 1:07 pm
by Robin Leadbeater
Hi Peter,

Were you definitely on the star and did you subtract the background close to the target to eliminate contamination from the galaxy?

Cheers
Robin

Re: 2020leu - Supernova in NGC 5363

PostPosted: Sat May 30, 2020 1:10 pm
by Peter Velez
Robin Leadbeater wrote:Hi Peter,

Were you definitely on the star and did you subtract the background close to the target to eliminate contamination from the galaxy?

Cheers
Robin


Definitely on the star - might have been contaminated. The data from this evening looks better - will get to the bottom of this soon enough

Pete

Re: 2020leu - Supernova in NGC 5363

PostPosted: Sat May 30, 2020 11:28 pm
by Vincent Lecocq
hello,

just acquired now in NGC5363, what is this ? :)

Re: 2020leu - Supernova in NGC 5363

PostPosted: Sun May 31, 2020 2:20 am
by Peter Velez
Vincent

I fear I may have led you astray - it may be misreporting or perhaps its a simple misunderstanding on my part.

The discovery report seems to be internally inconsistent. The report suggest the SN candidate is in NGC5363. It also states that it is just over 6 arcseconds from the core of the galaxy. I identified a bright object on the fringe of the galaxy and imaged that.

However, the reported co-ordinates for this potential SN are about 15 arcminutes away from the galaxy. This is quite some distance from where I was imaging.

I took another 2 sets of spectra of the target last night - because clouds came and went I only managed one set early in the evening when the target was quite low and another near the meridian. The later images weren't particularly clear so I have presented the spectrum from early on 30 May and another spectrum from the previous day.

Robin suggested a comparison with a standard K star which was a reasonable match. Adjusting for the reported RV of NGC 5363, I was able to match up quite a few lines with a K3I Pickles spectrum. He also suggested that I might have imaged the galaxy itself rather than the SN target.

I believe elliptical galaxies are characterised by a reasonably flat continuum with a steep drop off at around 4000 A. Prominent absorption lines are often Ca II, the Ca G band, Mg at 5157, Fe II at 5169 and Na I at 5896. Here are the 2 spectra with these lines identified. The spectra have been adjusted for the galaxy's reported RV of 1,129 km/s.

To my untrained eye, this looks like a reasonable match. It may be that there is also a foreground star that I have captured and so the spectrum is the combination of the star and galaxy. I've added the K3I spectrum in a separate plot.

Does this make sense? Comments are welcome - I am still finding my way with both processing and analysing my results.

Pete

Re: 2020leu - Supernova in NGC 5363

PostPosted: Tue Jun 02, 2020 10:47 am
by Robin Leadbeater
Hi Peter,

Stellar populations in elliptical galaxies are generally old so the integrated spectrum tends to look like a K star. The galaxy redshift is small but should be detectable in your spectrum so we can use this to distinguish between the galaxy and a foreground star. The Na D line appears to be at the galaxy redshift in your comparison with the redshifted K star but Na can also come from interstellar dust so may not be reliable. A better comparison is the Mg triplet at ~5175A which should be redshifted by ~20A if the target is in the galaxy.

There is a rather poor non response corrected spectrum of NGC5363 in NED
https://ned.ipac.caltech.edu/results?so ... NGC_5363_2
Here it is overplotted with Pickles K3v. The redshift in the Mg triplet is clear compared with the rest K3 spectrum.

ngc5363_NED_K3v.png
ngc5363_NED_K3v.png (12.95 KiB) Viewed 1191 times



Cheers
Robin

Re: 2020leu - Supernova in NGC 5363

PostPosted: Tue Jun 02, 2020 11:27 am
by Robin Leadbeater
Robin Leadbeater wrote:
There is a rather poor non response corrected spectrum of NGC5363 in NED


Here is a roughly rectified VSpec etc compatible dat file version if you want to compare it with your spectrum. (note it is of the galaxy core so shows some H alpha emission)