HARPS-N

HARPS-N
Name	HARPS-N
Caption	High Accuracy Radial velocity Planet Searcher for the Northern hemisphere
Operator	European Southern Observatory; Istituto Nazionale di Astrofisica; Harvard–Smithsonian Center for Astrophysics
Location	Roque de los Muchachos Observatory, La Palma
Wavelength	Optical
Type	Echelle spectrograph
Resolution	115,000
First light	2012
Status	Operational

HARPS-N is a high-precision, fiber-fed echelle spectrograph installed at the Roque de los Muchachos Observatory on La Palma, designed to measure stellar radial velocities with meter-per-second precision. Developed as a northern-hemisphere counterpart to an instrument at La Silla Observatory, it serves exoplanet searches, stellar astrophysics, and asteroseismology programs involving institutions such as Istituto Nazionale di Astrofisica, Centro de Astrobiología, and the Harvard–Smithsonian Center for Astrophysics. The instrument has been central to follow-up campaigns from space missions like Kepler and TESS, and to ground-based surveys coordinated with facilities including Subaru Telescope and W. M. Keck Observatory.

Overview

HARPS-N arose from a collaboration between European and American institutes to extend high-precision radial-velocity capability to the northern sky. Its development involved teams from Observatoire de Genève, Max Planck Institute for Astronomy, and the Instituto de Astrofísica de Canarias, with funding and technical contributions from agencies such as the Italian Space Agency and the European Research Council. Installed on the 3.58 m Telescopio Nazionale Galileo, the instrument complements northern photometric missions by providing velocity confirmation for candidates from Kepler and K2 and later TESS, while participating in follow-up of targets from surveys like SuperWASP and HATNet.

Instrument Design and Specifications

The spectrograph is a cross-dispersed echelle operating in the visible band, designed around a temperature- and pressure-stabilized vacuum enclosure to deliver long-term stability comparable to the southern instrument. The optical layout employs an R4 echelle grating, a white-pupil design, and two fiber inputs: one for target light and one for simultaneous reference or sky. Its spectral resolving power of ~115,000 covers roughly 383–693 nm across 69 orders, enabling precise measurement of Doppler shifts. The detector system uses a large-format CCD optimized for low read noise and high charge-transfer efficiency; the instrument control system integrates with the Telescopio Nazionale Galileo observatory software and adheres to calibration procedures standardized by teams at Observatoire de Genève and European Southern Observatory.

Key hardware features include a simultaneous thorium-argon or Fabry–Pérot calibration source, a double-scrambler fiber link to reduce modal noise, and active environmental control using cryogenic and thermal regulation subsystems developed in collaboration with groups at INAF and Harvard–Smithsonian Center for Astrophysics. The mechanical design emphasizes vibration isolation and minimal flexure to preserve line-spread function stability required for sub-1 m/s radial-velocity precision sought by programs from NASA and the European Space Agency.

Operation and Data Reduction

Observing operations follow queue-scheduled and service modes coordinated by the Telescopio Nazionale Galileo staff and science teams from partner institutions. Standard calibration sequences include nightly bias, flat-fielding, wavelength calibration with thorium-argon lamps or a Fabry–Pérot etalon, and periodic characterization using iodine-cell references established by studies at Carnegie Institution for Science. Raw frames are processed by a dedicated pipeline developed from heritage software at Observatoire de Genève and adapted by software teams at INAF and Queen Mary University of London.

The pipeline performs order extraction, blaze correction, cosmic-ray rejection, and wavelength solution derivation, producing 1D spectra and cross-correlation functions against numerical masks tailored for spectral types derived from catalogs such as Hipparcos and Gaia. Post-processing tools implement activity indicators (e.g., bisector span, chromospheric emission indices) to disentangle stellar activity from Keplerian signals, techniques refined in collaborations with groups at University of Geneva, University of California, Berkeley, and University of Cambridge. Time-series analyses utilize periodograms and Markov Chain Monte Carlo frameworks developed in parallel by researchers at University of Exeter and University of St Andrews.

Scientific Results and Discoveries

HARPS-N has confirmed and characterized numerous exoplanets, including low-mass super-Earths and Neptune-class planets, often in multi-planet systems identified by Kepler and TESS. Notable contributions include precise mass determinations that constrained internal compositions for transiting planets discovered by teams at MIT, Caltech, and University of Hawaii. The instrument enabled studies of planetary system architectures connected to host-star properties cataloged by Sloan Digital Sky Survey and APOGEE, and facilitated measurements of spin–orbit alignment when combined with transit photometry from Spitzer and ground-based facilities like Gran Telescopio Canarias.

Beyond exoplanets, HARPS-N advanced asteroseismology by detecting stellar oscillation modes in bright dwarfs and subgiants, complementing seismic analyses from Kepler and linking to stellar-evolution modeling performed by groups at Max Planck Institute for Solar System Research and University of Birmingham. It has also contributed to studies of stellar activity cycles, chromospheric variability surveys, and precise radial-velocity characterization of young stellar objects observed by teams at European Southern Observatory and Instituto de Astrofísica de Canarias.

Collaborations and Surveys

HARPS-N operates within international consortia and survey programs, collaborating with projects such as the Gaia-ESO Survey, radial-velocity follow-up networks supporting TESS and CHEOPS, and coordinated efforts with southern facilities to provide all-sky coverage. Institutional partners include INAF, Observatoire de Genève, Harvard–Smithsonian Center for Astrophysics, Queen Mary University of London, and the Istituto Nazionale di Astrofisica. Long-term programs like the Global Architecture of Planetary Systems (GAPS) consortium leverage HARPS-N for large observing campaigns, integrating expertise from investigators at University of Padua, University of Rome Tor Vergata, and University of Trento.

Category:Spectrographs Category:Exoplanet search projects