Reflected-light spectroscopy of nearby exoplanets with RISTRETTO at the VLT - Christophe Lovis University of Geneva - Zenodo
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The Very Large Telescope in 2030, ESO Garching, 17-20 June 2019
Reflected-light spectroscopy of nearby exoplanets
with RISTRETTO at the VLT
Christophe Lovis
University of Geneva
High-Contrast High-Resolution Spectroscopy in Reflected Light
Characterization of exoplanets around the nearest stars
Combining high-contrast
coronagraphy to high-resolution
spectroscopy in the visible/near-IR
directly detects the planet
reflected light and measures:
• True mass
• Albedo estimate
• Atmospheric composition
• Cloud properties
• Planet rotation
• Surface properties
• Atmospheric circulation
• Weather patterns
• Biosignatures
Lovis et al. 2017
High-Contrast High-Resolution Spectroscopy in Reflected Light
Characterization of exoplanets around the nearest stars
Combining high-contrast
coronagraphy to high-resolution
spectroscopy in the visible/near-IR
directly detects the planet
reflected light and measures:
• True mass
Proxima b (d = 1.3 pc) • Albedo estimate
Temperate rocky planet • Atmospheric composition
• Cloud properties
• Planet rotation
• Surface properties
• Atmospheric circulation
• Weather patterns
• Biosignatures
Lovis et al. 2017
High-Contrast High-Resolution Spectroscopy in Reflected Light
Characterization of exoplanets around the nearest stars
GJ 876 b (d = 4.7 pc)
Cool gas giant
Easiest HCHR target
Combining high-contrast
coronagraphy to high-resolution
spectroscopy in the visible/near-IR
directly detects the planet
reflected light and measures:
• True mass
Proxima b (d = 1.3 pc) • Albedo estimate
Temperate rocky planet • Atmospheric composition
• Cloud properties
• Planet rotation
• Surface properties
• Atmospheric circulation
• Weather patterns
• Biosignatures
Lovis et al. 2017
High-Contrast High-Resolution Spectroscopy in Reflected Light
Characterization of exoplanets around the nearest stars
GJ 876 b (d = 4.7 pc)
Cool gas giant
Easiest HCHR target
More nearby planets to be Combining high-contrast
found by the ESPRESSO, coronagraphy to high-resolution
SPiROU, NIRPS, spectroscopy in the visible/near-IR
CARMENES RV surveys directly detects the planet
reflected light and measures:
• True mass
Proxima b (d = 1.3 pc) • Albedo estimate
Temperate rocky planet • Atmospheric composition
• Cloud properties
• Planet rotation
• Surface properties
• Atmospheric circulation
• Weather patterns
• Biosignatures
Lovis et al. 2017
High-Contrast High-Resolution Spectroscopy in Reflected Light
Characterization of exoplanets around the nearest stars
High-Contrast High-Resolution Spectroscopy in Reflected Light
Characterization of exoplanets around the nearest stars
ELT-HIRES Science Priorities
Priority 1: Exoplanet atmospheres via transmission spectroscopy (potential detection of bio-
signatures)
TLR 1: R > 100,000, 0.5-1.8 μm, et alia; drive the HIRES baseline design
Enables: reionization of Universe; characterization of Cool stars
Doable: detection and investigation of near pristine gas; 3D reconstruction of the CGM; Extragalactic transients
Priority 2: Variation of the fundamental constants of Physics
TLR 2: blue extension to 0.37 μm
Enables: Cosmic variation of the CMB temperature, Determination of the deuterium abundance; investigation and
characterization of primitive stars
Priority 3: Exoplanet atmospheres via reflection spectroscopy (potential detection of bio-
signatures)
TLR 3: SCAO+IFU
Enables: Planet formation in protoplanetary disks; characterization of stellar atmospheres; Search of low mass Black
Holes
Doable: characterization of the physics of protoplanetary disks
Priority 4: Redshift drift (Sandage test)
TLR 4: ! accuracy 2 cm/s, stability 2 cm/s
Enables: Mass determination of exoplanets (Earth-like objects)
Doable: Radial velocity search for exoplanets around M-dwarf stars
17
Courtesy A. Marconi
ELT-HIRES Science Priorities
Priority 1: Exoplanet atmospheres via transmission spectroscopy (potential detection of bio-
signatures)
TLR 1: R > 100,000, 0.5-1.8 μm, et alia; drive the HIRES baseline design
Enables: reionization of Universe; characterization of Cool stars
Doable: detection and investigation of near pristine gas; 3D reconstruction of the CGM; Extragalactic transients
Priority 2: Variation of the fundamental constants of Physics
TLR 2: blue extension to 0.37 μm
Enables: Cosmic variation of the CMB temperature, Determination of the deuterium abundance; investigation and
characterization of primitive stars
Priority 3: Exoplanet atmospheres via reflection spectroscopy (potential detection of bio-
signatures)
TLR 3: SCAO+IFU
Enables: Planet formation in protoplanetary disks; characterization of stellar atmospheres; Search of low mass Black
Holes
Doable: characterization of the physics of protoplanetary disks
Priority 4: Redshift drift (Sandage test)
TLR 4: ! accuracy 2 cm/s, stability 2 cm/s
Enables: Mass determination of exoplanets (Earth-like objects)
Doable: Radial velocity search for exoplanets around M-dwarf stars
17
Courtesy A. Marconi
The RISTRETTO Project
high-Resolution Integral-field Spectrograph for the Tomography of
Resolved Exoplanets Through Timely Observations
Integral-field unit
VLT-AOF/SPHERE Ultra-fast 2nd-stage High-resolution
feeding
1st-stage AO correction AO correction spectrograph
monomode fibers
-> Pathfinder for ELT-HIRES: inform design of SCAO-IFU modePDS 70: circumstellar disk + planet with SPHERE (Keppler et al. 2018)
Sebastiaan Haffert et al. Nature Astronomy 2019
MUSE IFU (VLT) – R = 3000, moderate AO
Courtesy I. SnellenSecond planet!
Courtesy I. SnellenScience Cases for RISTRETTO • One high-risk high-gain objective: the detection of biosignatures on Proxima b • One « easy » target: studying the temperate giant planet GJ 876 b and demonstrating reflected-light exoplanet spectroscopy for the first time • Detailed studies of accretion processes onto forming proto-planets (spatially, dynamically, temporally) through H-alpha line emission • Solar System studies: spatially-resolved high-resolution spectroscopy of the surface of planets, icy moons (e.g. geysers), comets and minor bodies
RISTRETTO at the VLT: Technical Requirements
Top-level requirements
• Proxima b is the sizing science case
• Contrast requirement: 2x10-4 at 2.0
lambda/D at 700 nm (post-coronagraph)
• Strehl ratio > 50% at 700 nm
• Integral-field unit with multiplexing >= 7
covering the annulus at 2.0 lambda/D
• Wavelength range: 600-800 nm
• Spectral resolution > 150,000
XAO 2nd stage & fiber injection
• Pyramid wavefront sensor
• Ultra-fast AO loop (~3.5 kHz)
• Moderate number of actuators (~400)
• Optimized pupil-plane coronagraph
• Lenslet array + fiber injection module
AO simulations by M. Kasper (ESO)
High-resolution spectrograph
• Multiplexing >= 7
• Spectral sampling > 2.5 pixels FWHM
• Thermal & mechanical stability
• PSF stabilitySimulating Proxima b Observations: the Reflected Spectrum
Lovis et al. 2017Simulating Proxima b Observations: the Reflected Spectrum
How much time are you willing to invest to characterize a rocky planet in
the habitable zone around our closest neighbour?
1 ELT night?
2 ELT nights?
3 ELT nights?Simulating Proxima b Observations: the Reflected Spectrum
How much time are you willing to invest to characterize a rocky planet in
the habitable zone around our closest neighbour?
1 ELT night?
2 ELT nights?
3 ELT nights?
Well, that’s… 23 VLT nights
46 VLT nights
69 VLT nights!Detectability of the Reflected Spectrum
Detectability of the Reflected Spectrum Integration time for GJ 876 b: less than a night
RISTRETTO Optical Design
Work by B. Chazelas & S. Bovay (UniGE)
Main characteristics:
‣Wavelength range 620-840 nm
‣R >= 150,000
‣7 fibers IFU
‣4Kx4K 15 micron detector
‣Custom grating at ~20.36 l/mm and 70°
‣ Partnership with Canada (R. Doyon)
‣ Canada to procure, assemble and test the
spectrograph
‣ Hardware costs ~700-800 k€RISTRETTO at the Swiss 1.2m Telescope in La Silla • Being a diffraction-limited instrument, RISTRETTO can be adapted to any telescope with a good AO correction in the visible • Euler-AO is an independent project (PI: J. Hagelberg) with the goal of installing a simplified version of Robo-AO (PI: C. Baranec) on the Swiss telescope • Excellent opportunity to test RISTRETTO on- sky and demonstrate performances before going to the VLT • Euler-AO to be installed end of 2019
Robo-AO at the Palomar 1.5m Telescope
Courtesy J. HagelbergEuler-AO
Expected AO performance
No AO RoboAO@Kitt Peak
Simulations at 750nm
and 0.7” seeing
(U.Conod)
Jensen-Clem+ (2018)
18
Courtesy J. HagelbergRISTRETTO at the VLT: SPHERE or AOF ?
SPHERE pathway AOF pathway
Pros Pros
• Well-working instrument • Proposed as a visitor instrument on AOF
• Significant expertise and return of experience • Fast 2nd-stage AO system built from scratch
• « The » XAO instrument at the VLT with few external constraints (e.g. RTC)
• Faster development / less expensive?
• More freedom to explore new techniques and
Cons risky options
• ESO instrument in operation
• Not originally designed for allowing an AO Cons
upgrade, nor a visible fiber link port
• Proposed SPHERE+ upgrade only for IR arm • Needs a free slot on UT4 Nasmyth focus
• Difficult to change SAXO
• Needs another 2nd-stage AO system for the
visible arm (high complexity, limited space)RISTRETTO as a Visitor Instrument on UT4
Nasmyth A
Currently:
HAWK-I
From 2025 (?):
MAVIS
Window of opportunity: 2023-2025 (early de-commissioning of HAWK-I)RISTRETTO: Implementation Plan Setup at the VLT • Use of standard AOF infrastructure for 1st-stage AO correction (DSM, WFS, RTC), on-axis correction with natural guide star (LGS interesting?) • Re-use/copy of GRAAL/ERIS components? • Development of an independent 2nd-stage AO system based on commercially-available components wherever possible (e.g. Boston DM, OCAM2K camera) Timeline • 2019-2022: Design and construction phase (spectrograph, fiber link, IFU, coronagraph, 2nd-stage AO system) • 2020-2021: Proposal to ESO and its committees • 2022: Installation on the Swiss 1.2m telescope in La Silla, on-sky demonstration, performance validation • 2023: Installation on UT4 as a visitor instrument (early de-commissioning of HAWK-I)
Summary • RISTRETTO is a proposed visitor instrument at the VLT for pioneering reflected-light spectroscopy of exoplanets • The potential of this technique with ELT-HIRES is huge and may be the first to provide a detection of biosignatures • Additional science cases include accreting proto-planets and surface features of Solar System objects • Use VLT-RISTRETTO as a pathfinder for ELT-HIRES (and do interesting science with it!) • RISTRETTO to be first tested on the Swiss 1.2m telescope in La Silla • RISTRETTO to be installed at the Nasmyth A focus of UT4 in ~2023 • Visible XAO is a high-profile niche for the VLT and will likely remain so for a long time
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