NIRPS: Near Infra-Red Planet Searcher

NIRPS is an infrared extension of HARPS covering instantaneously the Y, J and H band (973.79 to 1808.53 nm). A K-Band extension is possible. NIRPS is a fibre-fed Echelle spectrograph with a spectral resolution of at least 80’000. NIRPS shall routinely deliver radial velocities with a precision of <1 m/s. Beyond this it can also be used as a general purpose spectrograph to observe objects as diverse as Comets or bright AGNs. The total efficiency at for blaze conditions (including atmosphere, telescope and slit losses for a 1 arcsec seeing in V band) shall be at least of 10%. It will be operated in parallel together with HARPS whereby the NIRPS arm will employ an adaptive optics system to maximize throughput while keeping the instrument size moderate. NIRPS will be deployed in two steps:

1.     retiring the old HARPS adaptor and replace it with the new one, including AO and new calibration unit

2.     erecting and commissioning of the NIRPS spectrograph in the 3.6m Coude-lab and commission it thereafter

The HARPS polarimetry will be maintained. NIRPS will come with a pipeline and all tools to provide science operations and data flow at the ESO/HARPS standard level. The NIRPS consortium will be reimbursed for building the instrument and operating it with ~50% of the available time. The rest, however, it is available to the ESO community for standard open time proposals.

nirps_overall

Organisation

PI-Institutes:

other participating institutions

The project team is composed of:

Principle Investigators:

Project Scientists:

  • Étienne Artigau, UdeM, Canada
  • C. Lovis, Observatoire de Genève, Switzerland
  • Xavier Delfosse, IPAG, France
  • Pedro Figueira, IA, Portugal
  • B. Canto, UFRN, Brazil
  • Jonay Hernandez, IAC, Spain

Project Management:

System Engineering:

  • François Wildi, Observatoire de Genève, Switzerland
  • Nicolas Blind (Front-End), Observatoire de Genève, Switzerland
  • Vlad Reshetov (Back-End), NRC, Canada

ESO represented by:

NIRPS optical layout
NIRPS optical layout

Schedule

Past milestones:

  • kick-off:             Jan. 2016
  • PDR:                Oct. 2016
  • FDR:                May 2017

Current status: under construction after FDR

Future milestones:

  • Front-End installation, La Silla    1st Q. 2019
  • Back-end integration, LaSilla      2nd Q 2019
  • First light                                 3rd Q 2019

 

Instrument Description

Calibration Unit:

The calibration system is a separate unit that contains all light sources necessary, controllers and injection optics. The unit is located at the Coude floor and calibration light is transmitted via optical fibers to the NIRPS Front End.
The will be two types of fibres (see below) for the two operations modes of NIRPS: This unit has its own control module for the various lamps and lasers, power supplies and motors. The whole calibration unit will be fitted into a standard rack and it comprises the following elements:

  • 2 fibre-coupled laser diodes at λ1 = 642 nm and λ2 = 1064 nm
  • 1 single mode fiber coupled laser diode λ3 = 642 nm
  • 2 Uranium-Neon lamps with two fiber outputs each
  • 1 Tungsten lamp with two fiber outputs each
  • External inputs to the unit so that a Laser Frequency Comb or a Fabry-Perot calibration source can be hooked up

The enclosed figure gives the schematic lay out of the unit.

cal_unit_block_diagram

Front End

The front-end comprises everything, which is mounted to the |Cassegrain focus of the 3.6m telescope. Three design principles have been followed:

  • HARPS related parts, especially HARPS POL shall in no way be compromised
  • the NIRPS spectrograph will be fed with fibres employing adaptive optics to improve the coupling efficiency; there will be two fibres which can freely be selected: a circular one (NA 0.125), feeding NIRPS in high dispersion mode (R~100000) and a octagonal one (320μm), feeding NIRPS in the high efficiency mode (R~80000) employing a pupil slicer to match the seeing limited input to the spectrometer;
  • there is an extra port to hook up an optional K-band spectrograph

The schematics of the front end can be seen in this figure:

Schematic of NIRPS optical beams and functionalities
Schematic of NIRPS optical beams and functionalities

To accommodate everything mechanically, the old HARPS adaptor and its interface will become history. They will be replaced by a completely new mechanical design.

NIRPS front end
NIRPS front end

Back End

The backend design is a high efficiency and high stability spectrograph illuminating eventually a 2kx2k HgCdTe detector. Detector mount and read-out system are a spin-off of a near-IR instrument of JWST (Fine Guidance Sensor/Near InfraRed Imager and Slitless Spectrograph (FGS/NIRISS),
https://jwst.nasa.gov/fgs.html ).

The spectrograph will have no movable parts.

The instrument packaged into the vacuum vessel:

Major structural elements inside vacuum vessel
Major structural elements inside vacuum vessel

The Echelle format shows, that the order numbers could be chosen such, that a high proportion of the detector area actually gets illuminated.

Order distribution on the detector
Order distribution on the detector

The image quality in the camera is excellent: compared to a pixel size of 18μm:  even in the extreme corners, image quality will be better than a fraction of one pixel while the spectrum will be slightly over-sampled (diameter of fibre corresponds to 3 pixel).

RMS spot radius (in micron) as a function of position on the detector
RMS spot radius (in micron) as a function of position on the detector

Scientific Objectives

Science case

The primary science case of NIRPS is, to extend the radio velocity searches from “normal” stars to red stars. The latter have two issues:

  1. they emit the maximum of their light in the near infrared spectral domain
  2. these stars are small, hence they are fully convective, which results in a lot of activity, i.e. the spectra are less stable.

For issue 1 it is obvious, that one wants to operate at a wavelength where the star emits most of its photons, Issue 2 is slightly more tricky, but also here we know, that the stellar spectra will be less perturbed by the stellar activity if one observes in the infrared, i.e. at wavelengths which ar not on the "blue" side of the Planck curve.

The quest for planet searches in the near IR stems from the fact, that, using the RV-method, it is much easier to detect Earth like planets in the habitable zone around these kind of stars then around Solar type stars. Moreover, our next door neighbours in the galaxy are mostly low-mass red stars.

Competing Instruments

Of course, given the promises, there is competition by at least the following instruments:

GIANO at the 3.5m TNG on LaPalma, in operation,

CARMENES at the 3.5m Telescope of Calar Alto, Spain, has just been commissioned

SPIROU at the 3.6m CFHT on Hawaii (to be commissioned later in 2017)

NIRPS, however, has two decisive advantages here: at first it is in the southern hemisphere with a higher abundance of candidate stars and secondly, due to the special arrangements to procure this instrument, NIRPS will get sufficient observing time, be it in GTO or in open time operations.