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High Precision Spectroscopy 2006 - LP
Why a new window now
High wavelength calibration accuracy…
Very accurate Doppler shift measurements…
Measurement of isotopic ratios…
High Precision Spectroscopy requires
very high S/N ratios
 photon starved
 Very and Extremely Large Telescopes
High Precision Spectroscopy 2006 - LP
ESO is operating the VLT…
Four 8 Meter telescopes
11 Instruments at Cass
or Nasmyth Foci +
Combined coherent
focus+VLTI +
Combined Incoherent
Focus (16m equivalent)
High Precision Spectroscopy 2006 - LP
And ESO is planning the E-ELT!
42 Meter
‘adaptive’
Telescope
First light
2015
High Precision Spectroscopy 2006 - LP
CODEX @ ELT
ESO:
G. Avila, B. Delabre, H. Dekker, S. D’Odorico,
J. Liske, L. Pasquini, P. Shaver
Observatoire Geneve :
M. Dessauges-Zavadsky, M. Fleury, C. Lovis, M. Mayor, F. Pepe,
D. Queloz, S. Udry
INAF-Trieste:
P. Bonifacio, S. Cristiani, V. D’Odorico, P. Molaro, M. Nonino, E. Vanzella
Institute of Astronomy Cambridge:
M. Haehnelt, M. Murphy, M. Viel
Instituto de Astrofisica Canarias:
R. Garcia-Lopez, R. Rebolo, M. Zapatero
Others:
F. Bouchy (Marseille), S. Borgani (Daut-Ts), A. Grazian (Roma), S. Levshakov
(St-Petersburg), L. Moscardini (OABo-INAF), S. Zucker (Tel Aviv),
High Precision Spectroscopy 2006 - LP
T. Wilklind (ESA)
Four Outstanding Cases
- Direct measurement of the dynamics of the Universe
- Cosmological variation of the Fine-Structure Constant:
CODEX will aim at an accuracy of ∆/ ~5x 10-9
- Terrestrial
planets in extra-solar systems: RV of
earth mass planets, spectroscopy of transits
- Primordial nucleosynthesis:
probing SBB
nucleosynthesis: primordial Li7, Li6/Li7
Many additional applications (as from this conference....):
Asteroseismology,Abundances in Stars, Variability of µ,
Temperature evolution of CMB, Chemical evolution of IGM..
High Precision Spectroscopy 2006 - LP
Dynamics of the Universe
Directly measure the expansion of the
Universe by observing the change of redshift
with a time interval of a few (10-20) years
”It should be possible to choose between various
models of the expanding universe if the deceleration of
a given galaxy could be measured. Precise
predictions of the expected change in z=dl/l0 for
reasonable observing times (say 100 years) is
exceedingly small. Nevertheless, the predictions are
interesting, since they form part of the available theory
for the evolution of the universe” Sandage 1962 ApJ
136,319
High Precision Spectroscopy 2006 - LP
Cosmic Signal
t0=actual epoch
In a homogeneous, isotropic
Universe a FRW metric
te=emission epoch
z
z
dz  dt0  dte
t0
te
dz z z dte a (t0 ) a (te ) a (t 0 ) 1
z   


dt0 t0 te dt0 a (te ) a (te ) a (te ) 1  z
z  (1  z ) H 0  H (te ).
H  H0 M (1  z)  R (1  z)    (1 tot )(1  z)
3
4
where tot  M  R     1

1
2
2
High Precision Spectroscopy 2006 - LP
Direct measurement !
• Bias-free determination of cosmological
parameters
• Different redshift (CMB, SNIa); measure
dynamics and not geometry
• Not dependent from evolutionary effects
of sources
• Legacy Mission to future astronomers
(First epoch measurements)
High Precision Spectroscopy 2006 - LP
High Redshift Supernovae..
SNae: observe magnitudes at different Redshifts
Assume SNae are standard candles at all z
Require non-trivial K corrections
Require determination of Reddening…
High Precision Spectroscopy 2006 - LP
The measurement concept …..
But this is for 107 years… Having much less time at
our disposal the shift is much smaller….
High Precision Spectroscopy 2006 - LP
The expected
acceleration
Is SMALL!
Note: the standard
model was not
always standard..
The change in sign is the signature of the non zero
cosmological constant
High Precision Spectroscopy 2006 - LP
Results of Simulation (..)
Simulating the dependence on Z
Information
“saturates”:
a) Too many lines
b) High Redshift
makes them
broader.
High Precision Spectroscopy 2006 - LP
Results of simulations (…)
Many simulations have been carried out independently by 3
groups; using observed and fully simulated spectra. A very
good agreement is found, and we can produce a simple
scaling law:
v = 1.4*(2350/(S/N))(30/NQSO)0.5 (5/(1+Z))1.8 cm/sec
Where v is the total uncertainty (difference between 2
epochs) while the other parameters refers to the
characteristics of one epoch observation; Pixel size
considered: 0.0125. About half of the signal is coming from
the metal lines associated to the Ly
High Precision Spectroscopy 2006 - LP
Result of simulations (……)
The full experiment
NQSO = 30
randomly distributed in the range 2 < zQSO <4.5
S/N = 3000 per 0.0125 Å pixel/epoch (no metal lines used)
t = 20 years
Green points: 0.1 z bins
Blue: 0.5 z bins
Red line: Model with
H0=70 Km/s/Mpc
Ωm=0.3 Ω=0.7
The cosmic signal is
Detected at >99%
significance(!)
High Precision Spectroscopy 2006 - LP
Scaling with telescope diameter
20 yrs baseline
With a telescope in the
range of the 30-40m
the experiment will be
possible:
1) With a timeline of 20
yrs the accuracy scales
to 2 cm/sec
2) Use the full spectral
range, including the
Ly region
VLT and Keck have devoted already > 1000 h each to QSOs..
High Precision Spectroscopy 2006 - LP
CODEX design parameters
Location
Telescope diameter
Feed
Overall DQE
Entrance aperture
Wavelength range
Spectral Resolution
Number of Spectrographs
Main disperser
Crossdisperser
Camera
CCD
Underground in nested stabilized environment
42 m
Coude’ + Fibre or Fibre only
20% Coude’ + Fibre , 13% Fibre only
1 arcsec
380 – 680 nm
150 000
3 (for 1 arcsec aperture at 42 m)
3 x R4 echelle 42 l/mm 160 x 20 cm
6 x VPHG 1500 l/mm 20 x 10 cm
6 x F/1.4-2.8
6 x 8K x 8K (15 um pixels)
High Precision Spectroscopy 2006 - LP
How to improve accuracy and stability
•
•
•
•
•
•
•
•
•
•
Scramblers to reduce effect of guiding errors
Image dissector, multiple instruments
Simultaneous wavelength calibration
Use of wavelength calibration based on “laser comb”
Fully passive instrument, ultra-high temperature stability
Instrument in vacuum tank
High precision control of detector temperature
Underground facility, zero human access
Blaze Correction and Flat Fielding
System PRECURSOR @ VLT
High Precision Spectroscopy 2006 - LP
CODEX laboratory floor plan
Underground hall 20 x 30 m; height 8 m
1K
Instrument room 10 x 20 m; height 5 m
0.1 K
Instrument tanks, dia. ~ 2.5 x 4 m,
0.01 K
Optical bench and detector
0.001 K
Control room and aux. equipment (laser)
1K
High Precision Spectroscopy 2006 - LP
Telescope Link: Transmission
The case was studied for the combined focus of the
4 VLT telescopes: Coude’ train is the most efficient
solution and the only one which preserves the BLUE
70
60
Total efficiency
50
40
30
20
Full fibre
Fibre-Optics
10
Full optics
Optics-Fibre
0
360
410
460
510
560
610
660
Wavelength (nm)
High Precision Spectroscopy 2006 - LP
CODEX Unit Spectrograph
Light from fibres
enters here
B. Delabre ESO
High Precision Spectroscopy 2006 - LP
Calibration System: Laser Frequency Comb
Metrology labs recently revolutionized by introduction
of femtosecond-pulsed, self-referenced lasers driven by
atomic clock standards
I(1)
n
Cesium atomic clock
(or even GPS signal!)
n
2n
2n
Result is a reproducible, stable “comb” of evenly spaced
lines who’s frequencies are known a priori to better than 1
in 1015
High Precision Spectroscopy 2006 - LP
Comb: spectra simulations R=100k, n=15GHz,
l=5000Å
Total velocity precision better than 1cms-1 in
a single shot for SNR ~ 1000 (4500-6500Å)
Running study with MPQ (Nobel Prize 2005)
High Precision Spectroscopy 2006 - LP
Precision Spectroscopy @ ELT
Extremely Large Telescopes will provide for the first time
enough photons to guarantee a quantum jump in high
resolution spectroscopy
To open these new windows, High Resolution must be coupled
to extremely high accuracy and stability
We have developed a design for such an instrument, and we will
propose ESPRESSO, the CODEX precursor @ the VLT
High Precision Spectroscopy 2006 - LP
Laser Comb: Advantages and Challenges
Advantages:
 Absolute calibration
 Long term frequency stability
 Evenly spaced and highly precise frequencies allow
mapping of distortions, drifts and intra-pixel sensitivity
variations of CCD
Naturally fibre feed system. HARPS prototype possible.
Challenges:
Line-spacing currently limited to ~1GHz. We need ~10–15
GHz...
Large spectral range required (380-680 nm): Existing
technology can possibly be extended.
High Precision Spectroscopy 2006 - LP
Peculiar motions at the Earth
Parameter
Induced error on the
correction [cm s-1]
Comment
Earth orbital velocity
- Solar system ephemerides
< 0.1
JPL DE405
Earth rotation
- Geoid shape
- Observatory coordinates
- Observatory altitude
- Precession/nutation corrections
~ 0.5
< 0.1
< 0.1
< 0.1
Any location in atm. along
photon path may be chosen
Target coordinates
- RA and DEC
- Proper motion
- Parallax
?
~0
~0
70 mas  1 cm s-1
negligible
negligible
Relativistic corrections
- Local gravitational potential
< 0.1
Timing
- Flux-weighted date of observation
?
0.6 s  1 cm s-1
The solar acceleration in the Galaxy will be measured with an
accuracy of ~ 0.5 mm/sec/yr by GAIA High Precision Spectroscopy 2006 - LP
Why measure dynamics?
All the results so far obtained in the ‘concordance model’ assumes
that GR in the FRW formulation is the correct theory.
l~0.7 : but we do not know what l is and how it evolves.
If GR holds, geometry and dynamics are related, matter and
energy content of the Universe determine both.
Dynamics has, however, never been measured.
All other experiments, extremely successful such as
High Z SNae search and WMAP
measure geometry: dimming of magnitudes and scattering at the
recombination surface.
High Precision Spectroscopy 2006 - LP
Challenges & Feedback
Calibration source, stable, reproducible, equally spaced..
LASER COMB
CCD control (thermal… )
High throughput of the spectrograph and injection system:
EFFICIENT COUDE’ FOCUS
Light scrambling capabilities (1 cm/sec  0.0000003
arcsec centering accuracy on a slit…)
TELESCOPE POINTING AND CENTERING ~0.02 arcsec
System aspects (from pointing to calibration to data reduction)
ALL aspects strongly suggest extensive prototyping
High Precision Spectroscopy 2006 - LP
BASIC SPECTROGRAPH REQUIREMENTS
Once QSOs are established targets, through basic
knowledge and simulations we determine the
spectrograph parameters.
Spectral range: QSO in the range Z~1.5 - 5. At higher Z too many
absorbers wipe out information, Ly is visible from earth at Z>1.8
For lower Z, metal lines only can be used. But to span a large Z range is
important also to link it to lower Z experiments: ideal range 300-680
nm. UV: trade-off (less sensitivity, few Ly absorbers..)
Resolving Power: Ly line have a typical width of 20-30 Km/sec
and R=50000 would suffice. Higher spectral resolution is required by
metallic lines (b<~3 Km/sec) and by calibration accuracy requirement;
R~150000
Such a resolution is challenging for any seeing limited ELT: the final
number will be a trade off between size, sky aperture, detector noise…
High Precision Spectroscopy 2006 - LP
CODEX Image and Pupil Evolution
Several new features :
Equivalent fiber 480 x 120
Fiber 120 x 120 _m
_m
Anamorphic
collimator
Anamorphic
collimator
F/2.4
Pupil 40 x 160 mm
START
Pupil slicer
Pupil Slicer
Camera
fiber 1680 x 210 _m
Pupil 200 x 400 mm
(on echelle grating)
Anamorphic
VPH
Ratio 2.25
Equivalent fiber 740 x 210
_m
Pupil 154 x 131 mm
F/2.2 x 2.5
Anamorphic
Crossidsperser
(Slanted VPH)
Fiber image
212 x 60 _m
CODEX
DETECTOR
High Precision Spectroscopy 2006 - LP
Standard Cosmological Model
With the assumptions of homogeneity and
isotropy, the concordance model finds a FRW
metric with a non zero cosmological constant
High Precision Spectroscopy 2006 - LP
How to Measure this signal?
Masers : in principle very good candidates: lines are very narrow
and measurements accurate: however they sit at the center of huge
potential wells: large peculiar motions, larger than the Cosmic
Signal are expected
Radio Galaxies with ALMA : The CODEX aim has been independently
studied for ALMA: as for Masers, local motions of the emitters are
real killers. Few radio galaxies so far observed show variability at a
level much higher than the signal we should detect
Ly forest: Absorption from the many intervening lines in front of high Z
QSOs are the most promising candidates. Simulations, observations and
analysis all concur in indicating that Ly forest and associated metal
lines are produced by systems sitting in a warm IGM following
beautifully the Hubble flow !
High Precision Spectroscopy 2006 - LP
Results of simulations (1)
Simulating the dependence on resolution
( Ly forest only)
Above a R~50000 there
is no more gain for the
Ly Forest. Higher
Resolution is required
by metal lines and
Calibration accuracy.
High Precision Spectroscopy 2006 - LP
Results of simulation (2): real spectrum
Dependence on cumulative S/N/pixel (0.015 A)
High Precision Spectroscopy 2006 - LP
Can we do it ?
Telescope + Instrument
Efficiency required to
complete the experiment
under the following
assumptions:
•V=16.5 QSO
• 36 QSO each S/N 2000
(0.015 pixel), for a total of
• 2000 obs. hs/epoch
( 1cm/sec/yr)
Red line: VLT+UVES
peak efficiency
In 1st approx. precision
scales as D for a given
efficiency.
High Precision Spectroscopy 2006 - LP
PECULIAR MOTIONS
Ly = vacc~100 Km/sec Tacc~109 yr.. negligible
Metal systems associated to damped Ly:vacc~3-400
Km/sec Tacc~108 BUT hundreds systems-statistically level
out
Different from the maser and radio-galaxy case… Calls for
many line of sight
High Precision Spectroscopy 2006 - LP
PECULIAR MOTIONS: Simulations
Detailed, state of
the art
hydrodynamical
simulations confirm
that the effects are
negligible
High Precision Spectroscopy 2006 - LP
What’s new
• VLT-UVES & Keck HIRES observed hundreds
of QSOs at High Res (R>40000), z between 2 and
5, V=16-18. Ly clouds have been extensively
simulated: their hot gas belongs to the IGM and
they trace the Hubble flow
• Exoplanets (HARPS) long term accuracy 1m/s,
short term (hours) 0.1m/s (and largely
understood)
• ELT !! LOT OF PHOTONS (we need them!!)
High Precision Spectroscopy 2006 - LP
Verification of targets and reference mission
QSO have been selected
from existing catalogues and
compilations (Veron, SDSS )
Selection criteria: magnitude
and z
Magnitudes: redwards of Ly,
selected band depends on z
In this Figure only the 5
brightest QSOs of each 0.25 z
bin are shown. Hypothesis:
e.g. 2000 h observations with
an 80 m telescope and 14%
efficiency; all QSO brighter or
around the iso-accuracy lines
are suitable.
High Precision Spectroscopy 2006 - LP
Fiber feed + Pre-slit
Entrance aperture 1” on 60 m or 0.65” on 100 m
37 Fibres array, 8 fibres/spectrograph
OWL
Lightpipe: forming an
homogeneously illuminated
Slit & scrambling
High Precision Spectroscopy 2006 - LP
CODEX @ ELT
More info & discussion at the
Aveiro Conference on
Precision Spectroscopy
in Astrophysics
11-15 September 2006,
Aveiro, Portugal
http://www.oal.ul.pt/psa2006
High Precision Spectroscopy 2006 - LP
Results of simulations (….)
The full experiment
DT=10 yrs
1500 Hours
Metals
V=16.5
Eff. 15%
High Precision Spectroscopy 2006 - LP
QSO absorption lines
Quasar
To Earth
Lyman limit
Ly
Ly
Lyem
SiII CII
SiII CIV
SiIV
Lyem
NVem
CIVem
SiIVem
High Precision Spectroscopy 2006 - LP