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 SNcandidate 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• 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 Ia @ 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)

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

A great team!