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HARPS ... North. Francesco Pepe et al. Geneva Observatory, Switzerland. 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

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HARPS ... North

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Harps north

HARPS ... North

  • Francesco Pepe et al.

Geneva Observatory, Switzerland

What s harps

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

The doppler measurement

The Doppler measurement

cross-correlation mask

Error sources

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

Stellar noise p modes

Stellar “noise”: p-modes

Stellar noise p modes1

Stellar “noise”:p-modes

Stellar noise activity

Stellar “noise”: Activity

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Contaminants: Atmosphere

Photon noise

Photon “noise”

  • Is NOT only SNR !!!!

  • Spectral resolution

  • Spectral type

  • Stellar rotation

Contaminants close by objects

Contaminants: Close-by objects

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Photon “noise”:

Spectral information


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Photon “noise”:

Spectral resolution

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Photon “noise”:

Stellar rotation

Instrumental errors

Instrumental errors

  • External

    • Illumination of the spectrograph

  • Internal

    • “Motion” of the spectrum on the detector

Limitations telescope centering and guiding

Limitations:Telescope centering and guiding

Stored guiding image for QC

Slit spectrograph

1 arcsec


Limitations light feeding


Guiding error:

0.5’’ → 2-3 m/s

for a fiber-fed spectrograph

Fiber-fed spectrograph

Fiber entrance

Image scrambler

Fiber exit

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Instrumental stability

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

Design elements

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

Instrumental stability

Instrumental stability

Line and instrumental stability

Line (and Instrumental) stability

Absolute position on the CCD of a Th line over one month

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Simultaneous reference



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Object spectrum

ThAr spectrum

Wavelength calibration

Object fiber

ThAr reference

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RV (object) =

RV (measured)







RV (measured)


Object spectrum

ThAr spectrum


Object fiber

ThAr reference

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Simultaneous reference

The wavelength calibration

The wavelength calibration


Instrumental errors calibration

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

Calibration the problem of blends

Calibration: The problem of blends

Isolated lines are very rare!

Fit neighbouring lines simultaneously with multiple Gaussians

But harps n is also

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

Limiting factors and possible improvements

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)

Subsystem break down

Subsystem break-down






Spectrograph room

Isolation box

Fiber run




Vacuum system


Subsystem opto mechanics

Subsystem: Opto-mechanics

Subsystem detector

Subsystem: Detector

Subsystem exposure meter

Subsystem: Exposure meter

Exposure meter

Exposure meter

Subsystem vacuum system

Subsystem: Vacuum System

Subsystem fiber run

Subsystem: Fiber run

Subsystems front end hw sw

Subsystems: Front end, HW, SW


Calibration fibers (0.3mm dia.)

Interfaces cfa og

Interfaces CfA - OG

  • Detector - Spectrograph

  • Fiber run - Front end

  • Vacuum System - HARPS Room/Enclosure

  • Electronic components

Detector spectrograph

Detector - Spectrograph

  • Chip position and tilt

  • Field-lens tilt

  • Electrical connectors and cables

  • Front-amplifier size and location

  • -> ICD between SP and DU

Fiber run front end

Fiber run - Front end

  • Fiber-hole position(s)

  • Mirror position and tilt

  • Mirror shape (possibly flat !)

  • -> ICD between FR and FE

Vacuum system spectrograph room

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

Spectrograph electronics

Spectrograph electronics

  • Elements 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)

Best wishes to harps n

Best wishes to HARPS-N

3 level concept

3-level concept

Spectrograph room: +- 0.2 K



Isolation Box: +- 0.01 K

Spectrograph: +- 0.001 K

Spectrograph room

Spectrograph room

  • Model : YORK YEB 3S

  • Serial Nr. : 135.157.DN003

Room thermal control

Room thermal control

Temperature control

Temperature control

  • Lakeshore 331S T-controller + diode sensors + heaters

  • 80 mm polysterene panels

  • Thermal load on Room: 10 W/K

Performances but

Performances, but ...

Leassons learned

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

Project schedule og

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

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