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Extracting a SN spectrum from EMMI

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?.

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Extracting a SN spectrum from EMMI

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

  2. 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.”

  3. What was the problem? • Determine the mean density of the universe ΩM • Measure the expansion rate in the distant universe • Classification of distant SNeIa • Spectroscopy of distant SNeIa • “only” 4m telescopes available, except Keck

  4. Distant SN searches in 1995 • Two teams • SN Cosmology Project • High-z SN Search Team • HzTeam • 3 months searching with CTIO 4m MosaicCamera • Last night 30 March • First NTT night 2 AprilEMMI/RILD

  5. Observing SN 1995K 3 April 1995 • EMMI image • only SNcandidate forthe night • plenty of time for the integration Slit position2h integration Slit position2.5h integration

  6. 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

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

  8. 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!

  9. It worked! • SN Ia @ z=0.478

  10. ESO’s contribution to the first set of distant SNeIa

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

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

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

  14. 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 250000 SNe Ia per year?

  15. 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

  16. A great team!

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