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• 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!