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Extracting a SN spectrum from EMMI Thank you Sandro (and Hans, Jean-Louis, Gianni and the EMMI team)
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Transcript of Extracting a SN spectrum from EMMI Thank you Sandro (and Hans, Jean-Louis, Gianni and the EMMI team)
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 ΩM
• 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 MosaicCamera
– Last night 30 March– First NTT night 2 April
EMMI/RILD
Observing SN 1995K
• EMMI image– only SN
candidate forthe night
– plenty of time for the integration
3 April 1995
Slit position2h integration
Slit position2.5h 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
• 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!
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)
tobs [days]
Blondin et al. (2008)
35 spectra of13 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 250000 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