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

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 nm Sampling: 4 px per geometrical SE (3.3 real) Environmental control Drift measurement via simultaneous thorium

The Doppler measurement cross-correlation mask

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”: Activity

Contaminants: Atmosphere

Photon “noise” Is NOT only SNR !!!! Spectral resolution Spectral type Stellar rotation

Contaminants: Close-by objects

Flux Photon “noise”: Spectral information

Photon “noise”: Spectral resolution

Photon “noise”: Stellar rotation

Instrumental errors External ✴ Illumination of the spectrograph Internal ✴ “Motion” of the spectrum on the detector

Limitations: Telescope centering and guiding Slit spectrograph Δ RV 1 arcsec Stored guiding image for QC

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

ΔRV = 1 m/s Δ  = A 15 nm 1/1000 pixel ΔRV =1 m/s ΔT = 0.01 K Δp = 0.01 mBar Vacuum operation Temperature control Instrumental stability

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

Line (and Instrumental) stability Absolute position on the CCD of a Th line over one month

Object ThAr Simultaneous reference

Object fiber RV 0 ThAr reference Object spectrumThAr spectrum RV 0 Wavelength calibration

Object fiber RV 0 ThAr referenc e Object spectrum ThAr spectrum RV 0 Measurement RV (object) =- RV (measured) RV(drift)

Simultaneous reference

The wavelength calibration px

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 Isolated lines are very rare! Fit neighbouring lines simultaneously with multiple Gaussians

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 New calibration (and sim. reference) source Perfect guiding and/or scrambling, good IQ needed Improve detector stability (mounting, thermal control)

Subsystem break-down Isolation box Services Fiber run Detector Spectrograph room Adapter LCUs WS CfA OG ESO/OG Spectrograph Vacuum system

Subsystem: Opto-mechanics

Subsystem: Detector

Subsystem: Exposure meter

Exposure meter

Subsystem: Vacuum System

Subsystem: Fiber run

Subsystems: Front end, HW, SW Calibration fibers (0.3mm dia.) CfA

Interfaces CfA - OG I. Detector - Spectrograph II. Fiber run - Front end III. Vacuum System - HARPS Room/Enclosure IV. Electronic components

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-hole position(s) ✓ Mirror position and tilt ✓ Mirror shape (possibly flat !) -> ICD between FR and FE

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 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

3-level concept Spectrograph room: K Isolation Box: K Spectrograph: K 15°C 17°C

Spectrograph room Model : YORK YEB 3S Serial Nr. : DN003

Room thermal control

Temperature control ✓ Lakeshore 331S T-controller + diode sensors + heaters ✓ 80 mm polysterene panels ✓ Thermal load on Room: 10 W/K

Performances, but...

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 2008: Procurement of components 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: Integration and tests OG