at2017iji /ASASSN-17pk - Urgent request for spectra

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Robin Leadbeater
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at2017iji /ASASSN-17pk - Urgent request for spectra

Post by Robin Leadbeater »

I have had an urgent request from the ASAS-SN team for a spectrum of this bright (mag 15) transient ASASSN-17pk in ngc4174
https://wis-tns.weizmann.ac.il/object/2017iji
SDSS finder chart here
http://skyserver.sdss.org/dr14/en/tools ... ale=0.1981
It may possibly be a rare Tidal Disruption Event. It is a potential target for ALPY/LISA but I will be clouded out for the next days here. Would anyone else like to try? (It is in the galaxy core but probably bright enough to dominate the galaxy spectrum)

Thanks
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
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Re: at2017iji /ASASSN-17pk - Urgent request for spectra

Post by Robin Leadbeater »

Now confirmed as a type Ia Supernova

Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Forrest Sims
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Re: at2017iji /ASASSN-17pk - Urgent request for spectra

Post by Forrest Sims »

Here is my attempt trying to get spectrum data on ASASSN-17pk. This is a tough target! Besides standing up at 04:15 to get the target at about 45 deg altitude, I could not get acceptable guiding on the target on the slit. So I resorted to guiding on a nearby star in the guider field. The two big spikes in the spectrum at about 4357A and 5460A are puzzling. I inspected each raw image in both ISIS and in MaximDL and found no hot or even warm pixels within the binning zone at these X axis locations. However they do coincide very closely with HG1 lines from local light pollution. Any ideas?

Thanks!

Woody
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Francois Teyssier
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Re: at2017iji /ASASSN-17pk - Urgent request for spectra

Post by Francois Teyssier »

Nice spectrum of a difficult target Woody!
Difficult to remove bad pixels during the reduction with a very low SNR
I suggest:
fine tuning of LISA in order to get orthogonal spectrum and slit
then rotate the science camera in order to get vertical slit even if the spectrum is not perfectly horizontal (better to get sky lines perfectly vertical)
See : http://spectro-aras.com/forum/viewtopic.php?f=8&t=1912
Hg hypothesis: get a spectrum of light pollution and compare
All the best,
François
Robin Leadbeater
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Re: at2017iji /ASASSN-17pk - Urgent request for spectra

Post by Robin Leadbeater »

Hi Woody,

Yes definitely good enough to classify it. I generally prefer the program SNID for classification now but a simple way is to sign up to GELATO and upload it there to see what that gives
https://gelato.tng.iac.es/gelato/

Sharp w shaped defects like this are typical of sky line subtraction with a small error in the slant or smile correction. (rerunning the reduction with sky subtraction switched off will show their location) The averaged lines in the background regions become smeared slightly making them broader and shallower than in the spectrum so giving a mismatch when subtracted. (The problem is even greater with the ALPY where the lines are curved so cannot be corrected by adjusting the spectrograph as Francois suggests). You might be able to improve your defects by manually fine tuning the slant slightly and rerunning the reduction. (Also, as well as the spectrum profile, look at the background regions in the processed image that ISIS produces. If the subtraction is perfect there should be no signs of the sky lines in these regions, particularly close in around the spectrum)


Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
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Re: at2017iji /ASASSN-17pk - Urgent request for spectra

Post by Robin Leadbeater »

Also this object is embedded in the galaxy core so there is likely to be some contamination from the host galaxy spectrum which is difficult to subtract without a spectrum of the galaxy without the supernova. If you look at the professional spectrum on TNS
https://wis-tns.weizmann.ac.il/object/2017iji
you can see several narrow absorption lines, possibly from the host galaxy. Using the tool there, you can see for example that some of them line up with H Balmer wavelengths after correction for the host redshift

Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Christian Buil
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Re: at2017iji /ASASSN-17pk - Urgent request for spectra

Post by Christian Buil »

A tip for difficult situations (fine and intense pollution lines) and nearly undersampled spectral: select the linear interpolation method from the Setup tab, the spline can produce some time artifacts in these situations. Test the possibility.

Christian
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