harps... north geneva observatory, switzerland francesco pepe et al
TRANSCRIPT
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HARPS ... North
Geneva Observatory, Switzerland
Francesco Pepe et al.
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What’s HARPS?
Fiber fed, cross-disperser echelle spectrograph
Spectral resolution: geometrical 84’000, optical 115’000
Field: 1 arcsec on the sky (HARPS-N: 0.9 arcsec!)
Wavelength range: 383 nm - 690 nm
Sampling: 4 px per geometrical SE (3.3 real)
Environmental control
Drift measurement via simultaneous thorium
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The Doppler measurement
cross-correlation mask
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Error sources
Stellar noise (or any other object)
Contaminants (Earth’s atmosphere, moon, etc.)
Instrumental noise
✴Calibration accuracy (any technique)
✴Instrumental stability (from calibration to measurement)
Photon noise
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Stellar “noise”: p-modes
- 2 . 5
- 2
- 1 . 5
- 1
- 0 . 5
0
0 . 5
1
1 . 5
2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1
T i m e [ h r s ]
Dispersion = 0.52 m/s
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Stellar “noise”:p-modes
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Stellar “noise”: Activity
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Contaminants: Atmosphere
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Photon “noise”
Is NOT only SNR !!!!
Spectral resolution
Spectral type
Stellar rotation
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Contaminants: Close-by objects
Bad seeing Good seeing
R V
R V
Fiber entrance
R V
RV
Large contamination
by secondary spectrum
Small contamination
by secondary spectrum
Possible dispersion up to several 100 m/s
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Flux
Photon “noise”:Spectral information
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Photon “noise”:Spectral resolution
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Photon “noise”:Stellar rotation
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Instrumental errors
External
✴Illumination of the spectrograph
Internal
✴“Motion” of the spectrum on the detector
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Limitations:Telescope centering and guiding
Slit spectrograph
Δ RV
1 arcsec
Stored guiding image for QC
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Limitations:Light-feeding
Fiber-fed spectrograph
Fiber entrance
Fiber exit
Image scrambler
Guiding error:
0.5’’ → 2-3 m/s
for a fiber-fed spectrograph
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ΔRV = 1 m/s
Δλ= 0.00001 A
15 nm
1/1000 pixel
ΔRV =1 m/s
ΔT = 0.01 K
Δp = 0.01 mBar
Vacuum operation
Temperature control
Instrumental stability
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Design Elements
Fiber feed (mandatory for this techniques)
Stable enviroment (gravity, vibrations, etc.)
Image Scrambling
No moving or sensitive parts after fiber
SIMPLE and ROBUST optomechanics
“Best” (reasonably) achievable env. control
✴Vacuum operation
✴Thermal control
High spectral resolution
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Instrumental stability
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Line (and Instrumental) stability
Absolute position on the CCD of a Th line over one month
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Object
ThAr
Simultaneous reference
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Object fiber
RV0
ThAr reference
Object spectrum ThAr spectrum
RV0
Wavelength calibration
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Object fiber
RV0
ThAr referen
ce
Object spectrum
ThAr spectrum
RV0
Measurement
RV (object) = -RV (measured)
RV (measured)
RV(drift)
RV(drift)
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Simultaneous reference
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The wavelength calibration
px
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Instrumental errors: Calibration
pixel-position precision
✴photon noise
✴blends
✴ pixel inhomogeneities, block stitching errors
accuracy of the wavelength standard
✴systematic errors, Atlas, RSF
✴instabilities (time, physical conditions: T, p, I)
accuracy of the fit algorithm
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Calibration: The problem of blends
Isolated lines are very rare!
Fit neighbouring lines
simultaneously with multiple
Gaussians
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But HARPS-N is also ...
... a software concept delivering full precision observables:
Scheduling many observations efficiently
Full quality pipeline available at the telescope
Fully automatic, in “near” realtime, RV computation
Link to data analysis
Continuous improvements and follow-up
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Limiting factors and possible improvements
New calibration (and sim. reference) source
Perfect guiding and/or scrambling, good IQ needed
Improve detector stability (mounting, thermal control)
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Subsystem break-down
Isolation box
Services
Fiber run
Detector
Spectrograph room
Adapter
LCUs
WS
CfA
OG
ESO/OG
Spectrograph
Vacuum system
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Subsystem: Opto-mechanics
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Subsystem: Detector
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Subsystem: Exposure meter
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Exposure meter
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Subsystem: Vacuum System
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Subsystem: Fiber run
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Subsystems: Front end, HW, SW
Calibration fibers (0.3mm dia.)
CfA
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Interfaces CfA - OG
I. Detector - Spectrograph
II.Fiber run - Front end
III. Vacuum System - HARPS Room/Enclosure
IV.Electronic components
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Detector - Spectrograph
✓ Chip position and tilt✓ Field-lens tilt✓ Electrical connectors and cables✓ Front-amplifier size and location
-> ICD between SP and DU
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Fiber run - Front end
✓ Fiber-hole position(s)✓ Mirror position and tilt✓ Mirror shape (possibly flat !)
-> ICD between FR and FE
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Vacuum system - Spectrograph Room
✓ Heat load on spectrgraph room✓ Rail-fixation plate✓ Location of services✓ Feed-through window through SR wall✓ Hoist > 2500 kg
-> ICD between VS and SR
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Spectrograph electronicsElements to be integrated in
SW: ✓ F-200 Temperature controller (conf.,
read)✓ Agilent pulse counter (conf., read)✓ Pfeiffer Digiline P-sensors (read)✓ Uniblitz shutter controller
(read/write)✓ Lakeshore T-controller for CCD
(conf., read)✓ Lakeshore T-controller for Isolation
Box (conf., read)✓ I-Omega T-controllers for CFC ->
temperatures and alarms (read)✓ LN2-level gauge (read)
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Best wishes to HARPS-N
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3-level concept
Spectrograph room: +- 0.2 K
Isolation Box: +- 0.01 K
Spectrograph: +- 0.001 K
15°C
17°C
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Spectrograph room
Model : YORK YEB 3S
Serial Nr. : 135.157.DN003
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Room thermal control
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Temperature control
✓Lakeshore 331S T-controller + diode sensors + heaters
✓80 mm polysterene panels
✓Thermal load on Room: 10 W/K
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Performances, but ...
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Leassons learned
Concept works well and is simple
Changing thermal load through feet produces gradient and seasonal effects
➡ Thermal isolation of feet
➡ Heater below feet, Tref = vacuum vessel
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Project schedule OG
2008: Procurement of components
04/2008 - 04/2009: Manufacturing of mechanical parts for vacuum and optics
01/2009: Start assembly
03/2009: Delivery of FA, DU and Control HW and SW by CfA to OG
04/2009 - 07/2009: Integration and tests OG