Extracting a SN spectrum from EMMI Thank you Sandro (and Hans, Jean-Louis, Gianni and the EMMI team)

ESO Press Release 95/11 “Beyond the Hubble Constant” “This demonstrates that SN 1995K is the most distant supernova (indeed, the most distant star!) ever observed.”

What was the problem? Determine the mean density of the universe Ω M Measure the expansion rate in the distant universe Classification of distant SNe Ia –Spectroscopy of distant SNe Ia –“only” 4m telescopes available, except Keck

Distant SN searches in 1995 Two teams –SN Cosmology Project –High-z SN Search Team HzTeam –3 months searching with CTIO 4m Mosaic Camera –Last night 30 March –First NTT night 2 April EMMI/RILD

Observing SN 1995K EMMI image –only SN candidate for the night –plenty of time for the integration 3 April 1995 Slit position 2h integration Slit position 2.5h integration

Data reductions Took over two months Tried everything in the book, but could not extract a good spectrum –2.5 hours without galaxy useless Galaxy contamination dominating –2-hour integration with galaxy at least gave me the SN location

Extracting the spectrum Thank you Sandro, Hans and Jean-Louis!

Extracting the spectrum Extracted a single row –Perfect alignment of the spectrum on the CCD Extracted spectrum still did not look like a supernova –Strong contamination by galaxy remained Arbitrarily subtracted fraction (1/10) of the galaxy spectrum and rebinned to lower resolution BINGO!

It worked! SN z=0.478

ESO’s contribution to the first set of distant SNe Ia

Time dilation SN 1995K clearly showed the time dilation due to cosmic expansion Leibundgut et al. 1996

Time dilation Observed Wavelength [Å] Spectroscopic clock in the distant universe Blondin et al. (2008) (z ~ 0.5)  t obs [days]

Blondin et al. (2008) 35 spectra of 13 distant SN Ia (0.28  z  0.62) 1.VLT [5] 2.ESSENCE [4] 3.Literature [3] 4.VLT SNLS [1]

Where are we? Already in hand –about 1000 SNe Ia for cosmology –constant ω determined to 5% –accuracy dominated by systematic effects reddening, correlations, local field, evolution Test for variable ω –required accuracy ~2% in individual distances –can SNe Ia provide this? can the systematics be reduced to this level? homogeneous photometry? handle SNe Ia per year?

ESO SN instrumentation Perfect fit with the focal reducers –At several telescopes EFOSC(1/2), EMMI, DFOSC, FORS –No complicated offsets required –Simple point and shoot –“if you cannot see it in the direct image don’t bother with the spectrum” (Jason Spyromilio) –Great advantage over other observatories Full set of spectrographs –UVES, X-shooter, ISAAC, SINFONI –Extremely important for SN 1987A

A great team!