HARMONI: the ELT's First-Light Near-infrared and Visible Integral Field Spectrograph
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ELT Instrumentation DOI: 10.18727/0722-6691/5215
HARMONI: the ELT’s First-Light Near-infrared and Visible
Integral Field Spectrograph
Niranjan Thatte 1 performance and good sky coverage, widths), chemical abundances and
Matthias Tecza 1 respectively (AO) capability has recently composition (via emission and absorption
Hermine Schnetler 2 been added for exoplanet characterisa- line ratios) and the physical conditions
Benoit Neichel 3 tion. A large detector complement (temperature, density, presence of shocks)
Dave Melotte 2 of eight HAWAII-4RG arrays, four of the emitting region (via line diagnostics).
Thierry Fusco 3, 4 choices of spaxel scale, and 11 grating In addition, specialist capabilities such
Vanessa Ferraro-Wood 1 choices with resolving powers ranging as molecular mapping for high contrast
Fraser Clarke 1 from R ~ 3000 to R ~ 17 000 make observations, or the use of deconvolution
Ian Bryson 2 HARMONI a very versatile instrument with knowledge of the point spread func-
Kieran O’Brien 5 that can cater to a wide range of tion (PSF) from AO telemetry extend the
Mario Mateo 6 observing programmes. areas where HARMONI will make a huge
Begoña Garcia Lorenzo 7 impact. Some examples are showcased
Chris Evans 2 in the last section of this article.
Nicolas Bouché 8 About HARMONI
Santiago Arribas 9
and the HARMONI Consortium a HARMONI will provide the ELT’s work- Spatial and spectral grasp
horse spectroscopic capability at first
light. A visible and near-infrared integral Figure 1a shows the spatial layout of the
1
epartment of Physics, University
D field spectrograph (IFS), it provides a HARMONI field of view (FoV) at its four
of Oxford, UK “point-and-shoot” capability to simultane- different spaxel scales, one of which
2
United Kingdom Astronomy Technology ously obtain a spectrum of every spaxelb may be selected on the fly. At any spaxel
Centre (UKATC), Edinburgh, UK over a modest field of view. Several differ- scale, HARMONI simultaneously observes
3
L aboratoire d’Astrophysique ent flavours of adaptive optics ensure spectra of ~ 31 000 spaxels in a con
de Marseille (LAM), France (near) diffraction-limited spatial resolution tiguous rectangular field. The common
4
Département d’Optique et Techniques of ~ 10 milliarcseconds over most of the wavelength range in each data cube is
Avancées (DOTA), Office National sky. ELT+HARMONI will transform the ~ 3700 pixels long, after accounting for
d’Etudes et de Recherches Aérospatial landscape of observational astronomy the stagger between adjacent slitlets and
(ONERA), Paris, France by providing a big leap in sensitivity and slit curvature. The spaxel scales range
5
Physics Department, Durham resolution — a combination of the ELT’s from 0.06 × 0.03 arcseconds per spaxel,
University, UK huge collecting area, the exquisite spatial limited by the focal ratios achievable in
6
Department of Astronomy, University resolution provided by the AO, and large the spectrograph cameras, to 4 × 4 milli-
of Michigan, USA instantaneous wavelength coverage cou- arcseconds per spaxel, set to Nyquist
7
Instituto de Astrofísica de Canarias (IAC) pled with a range of spectral resolving sample the ELT’s diffraction limit in the
and Departamento de Astrofísica, powers (R ~ 3000 to 17 000). NIR H band. Two other intermediate
Universidad de La Laguna, Tenerife, scales of 10 × 10 milliarcseconds per
Spain Over the last couple of years, HARMONI spaxel and 20 × 20 milliarcseconds per
8
Centre de Recherche Astrophysique has added substantially to the core spaxel allow the user to optimise for sensi-
de Lyon (CRAL), France instrument. The LTAO capability is part tivity, spatial resolution or FoV, as required.
9
Centro de Astrobiología – Instituto of the baseline, as is a high-contrast AO A larger FoV is particularly desirable when
Nacional de Técnica Aeroespacial, (HCAO) mode that aims to enable direct using the “nod-on-IFU” technique to
Consejo Superior de Investigaciones spectroscopy of extra-solar planetary achieve accurate sky background sub-
Científicas (CAB-INTA/CSIC), Madrid, companions. The University of Michigan traction, as it involves positioning the
Spain has joined as a new partner, providing object alternately in each half of the FoV.
a much needed cash injection, while the
Institut de Planétologie et d’Astrophysique The versatility in choice of plate scale
The High Angular Resolution Monolithic de Grenoble (IPAG) is funding the hard- is complemented by a large choice of
Optical and Near-infrared Integral field ware for HCAO. wavelength ranges and spectral resolving
spectrograph (HARMONI) is the visible powers, as shown in Figure 1b. HARMONI
and near-infrared (NIR), adaptive-optics- HARMONI is equally suited to spatially uses Volume Phase Holographic (VPH)
assisted, integral field spectrograph for resolved spectroscopy of extended tar- gratings for high efficiency. Each grating
ESO’s Extremely Large Telescope (ELT). gets and of point sources, particularly if has a fixed wavelength range, so needs
It will have both a single-conjugate their positions are not precisely known to be physically exchanged to change
adaptive optics (SCAO) mode (using (for example, transients), or if they are observing band. One of eleven different
a single bright natural guide star) and located in crowded fields. The data cube gratings can be chosen, which between
a laser tomographic adaptive optics obtained from a single integral field expo- them provide three different resolving
(LTAO) mode (using multiple laser guide sure can yield information about the powers (R ~ 3000, 7000 and 17 000)
stars), providing near diffraction-limited source morphology (via broad- or narrow- spanning the various atmospheric win-
hyper-spectral imaging. A unique high- band images), spatially resolved kinemat- dows in the NIR (atmospheric transmis-
contrast adaptive optics with high ics and dynamics (via Doppler shifts and sion is shown in grey in Figure 1b).
The Messenger 182 | 2021 7
ELT Instrumentation Thatte N. et al., HARMONI
a) Spaxel c) 50
30 mas 20 mas 10 mas 4 mas
60 mas
Field-of-view
6.12 arcsec
0.3 40
4.08 arcsec
0.82 arcsec
2.04 arcsec
9.12 arcsec 3.04 arcsec 1.52 arcsec 0.61 arcsec
Declination + 2.17 (degrees)
For non-AO and visible For optimal sensitivity Best combination for Highest spatial
observations (faint targets) sensitivity and resolution
Strehl ratio (%)
spatial resolution (diffraction limited)
1 milliarcsecond (mas) = 0.001 arcsec 0.2
Grating resolutions
b) 32 000
Atmosphere
16 000 VIS 20
Resolving power
IzJ
HK 0.1
8000 Iz
J
H
K
4000 10
z-high
H-high
K-high1
2000 K-high2 0.0
0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 0.0 0.1
Wavelength (μm) Right ascension + 150.05 (degrees)
Figure 1. a) Spatial layout of the HARMONI science Adaptive optics flavours information from the six lines of sight to
field, showing the spaxel sizes and fields of view
reconstruct the wavefront aberration for
at the four different spaxel scales. b) Spectral cover-
age and resolving power ranges for each of the The ELT is an adaptive telescope, with the on-axis path, and commands M4 and
11 HARMONI grating choices. The atmospheric M4 (a deformable mirror with over 5000 M5 to the appropriate shapes to eliminate
transmission is shown in grey. c) Expected AO per- actuators) and M5 (a fast tip-tilt mirror) the effect of the turbulence, providing a
formance (Strehl ratio) for the COSMOS deep field,
providing active correction of atmos- near diffraction-limited corrected wave-
observed with HARMONI LTAO in good seeing con-
ditions (0.43 arcseconds), illustrating the sky cover- pheric turbulence. The sensing of the front to the IFS.
age achieved for a typical patch of sky. wavefront aberrations is done by the sci-
ence instruments — better rejection of It is not possible to measure the image
common-mode disturbances such as flex- motion with LGS, so a separate natural
A fixed-length spectrum implies a natural ure and vibrations is achieved by splitting guide star (NGS) is needed to sense tip-
compromise between instantaneous the wavefront sensing light as close to the tilt and focus. A single off-axis NGS is
wavelength coverage and resolving power. science focal plane as possible. The sensed by HARMONI’s NGS System
One grating provides coverage at visible scheme used for wavefront sensing leads (NGSS), with a probe arm that patrols a
wavelengths (V and R bands), requiring a to HARMONI’s four distinct operating 1-arcminute-radius field centred on the
different set of detectors (CCDs instead modes: LTAO, SCAO, HCAO, and noAO — IFS FoV. The NGS position and focus are
of the HgCdTe arrays used in the NIR). the last providing no adaptive optics cor- sensed at several hundred Hz in the H
However, as AO correction works well rection of atmospheric turbulence. and K bands, while a slow “Truth Sensor”
only at longer NIR wavelengths, the spatial uses the J-band light from the same star
resolution achieved at visible wavelengths In LTAO operation, six laser guide star to eliminate any low-order wavefront
is close to seeing-limited, making the (LGS) sensors, each with 78 × 78 sub- errors introduced by the LGS. The NGSS
large spaxel count somewhat superflu- apertures, measure the wavefront aberra- is able to operate with stars as faint as
ous. Consequently, only half the FoV is tions at 500 Hz from six sodium laser HAB = 19, so that HARMONI’s LTAO sys-
offered at visible wavelengths, at all stars. The laser stars are located in an tem can provide excellent sky coverage
spaxel scales. asterism with a diameter of ~ 1 arcminute, — 75% of the sky at the south Galactic
which provides the best compromise pole (SGP) with Strehl exceeding 30% in
between peak performance and robust- the K band under median conditions of
ness to changing atmospheric parame- atmospheric turbulence (see Figure 1c for
ters. HARMONI’s AO Control System an example of LTAO sky coverage).
(AOCS) stitches together the wavefront
8 The Messenger 182 | 2021
Even better performance may be combination of a pupil-plane apodiser at half maximum (FWHM) of the seeing.
obtained by using HARMONI’s SCAO and a focal-plane mask. Because of 2 × 1 and 4 × 1 binning along the spatial
system, provided a single, bright, natural uncorrected atmospheric differential axis can be used to reduce readout times
guide star is present within 15 arcseconds refraction (chromatic beam shift), it is not for the CCD detectors, creating effective
of the science target of interest. SCAO possible to use classical coronagraphs to spaxels of 0.06 × 0.06 arcseconds and
can also deal with extended objects improve contrast. The novel design by 0.06 × 0.12 arcseconds, respectively, that
as AO reference “stars”, with slightly Carlotti et al. (2018) achieves good rejec- are a better match to the seeing FWHM.
degraded performance, as long as the tion of starlight — the goal being (post-
reference is less than 2.5 arcseconds processed) contrasts of > 10 6 at separa-
in diameter. Unlike the LTAO system tions < 0.2 arcseconds — whilst enabling Instrument description
(which uses an off-axis NGS), SCAO inner working angles (IWA) of less than
uses a dichroic that sends light in the 100 milliarcseconds for IFS spectroscopy. Figure 2b shows an overview CAD model
700–1000 nm range to a pyramid wave- HCAO works only with an on-axis NGS. of the HARMONI instrument. The instru-
front sensor operating at 500 Hz, with It uses the pyramid wavefront sensor of ment is ~ 8 m tall, and has a footprint of
longer wavelengths (1000–2450 nm) the SCAO system for sensing wavefront 5 × 6 m and a total weight of approxi-
available for spectroscopy with the IFS. aberrations, with a second ZELDA wave- mately 36 tonnes. The opto-mechanics
Both on-axis and off-axis NGS may be front sensor (N’Diaye et al., 2016) for of the IFS consists of the pre-optics scale
used. Optimal performance is achieved improved sensitivity in the high-Strehl changer, the integral field unit (IFU) and
for stars down to V = 12, with a limiting regime. Angular Differential Imaging (ADI) four spectrograph units. The IFU re-
magnitude of V ~ 17. A second SCAO will also be employed to reduce the arranges the light from the field into four
dichroic is available, albeit with a reduced impact of quasi-static speckles. Conse- 500-mm pseudo long slits, which form
patrol field of 4 arcseconds in diameter, quently, the HCAO mode drives the IFS the input to the four spectrograph units.
with a cut-in wavelength of 800 nm for rotator to track the pupil, rather than field The IFS opto-mechanics resides in a
spectroscopy, allowing observations that tracking as employed in all other modes. large cryostat, about 3.26 m in diameter
use z-band stellar absorption features as and 4 m tall (a cutaway view is shown in
diagnostics. At wavelengths where AO correction is Figure 2a), at a constant operating tem-
expected to be poor, or when AO cannot perature of 130 K to minimise thermal
The HCAO mode adds a high-contrast be used owing to weather or technical background. The NIR detectors (eight
capability to HARMONI, using a constraints, HARMONI’s noAO mode can 4096 × 4096-pixel HAWAII 4RG arrays)
provide “seeing-limited” performance. are operated at the lower temperature of
Figure 2. a) Cutaway CAD model of the HARMONI The noAO mode utilises a faint (I < 23) 40 K. The instrument rotator and cable
cryostat (ICR), situated on the instrument rotator
and cable wrap (IRW). The view shows the main
natural star for slow (~ 0.1 Hz) secondary wrap (IRW) allow the entire cryostat to
opto-mechanical components of the integral field guiding, eliminating slow drifts of the rotate about a vertical axis to follow field
spectrograph (IFS), namely the IFS pre-optics (IPO), instrument focal plane and ensuring rotation at the ELT’s Nasmyth focus. The
the integral field unit (IFU), and the spectrographs accurate pointing. This mode is typically vertical rotation axis guarantees an invari-
(ISP). b) overall CAD assembly of HARMONI, with the
various systems comprising the instrument coloured
expected to be used with the visible grat- ant gravity vector, improving the instru-
differently. The LSS is the LGSS Support Structure. ing and the coarsest spaxel scale, as all ment’s stability by minimising flexure.
Other acronyms are explained in the text. scales heavily oversample the full width
a) b) LGSS
IPO
LSS
FPRS
ICR ICR cold structure CM
ISS top frame
IFU
NGSS
IFS
rotating ISP
electronics ISS
cabinets main
frame
ICR
IFS
electronics
cabinets
IRW
IRW
The Messenger 182 | 2021 9
ELT Instrumentation Thatte N. et al., HARMONI
1 × 10 7 Figure 3. a) Reconstructed images of Io, observed
a)
with HARMONI at a scale of 4 × 4 milliarcseconds,
without deconvolution. The bottom image shows
two volcanic hot spots that dominate the NIR emis-
8 × 10 8 sion, while the top image is in a quiescent state.
Simulated spectra of four hot-spots at different tem-
peratures ranging from 600 K to 1200 K are also
Flux (electrons)
6 × 10 8 shown. b) Reconstructed image and spectrum
of a simulated Type-Ia supernova in a z ~ 3 galaxy,
located 0.2 arcseconds from the galaxy nucleus.
c) z ~ 6 galaxy from the NEW HORIZON cosmologi-
4 × 10 8 cal simulation, and its mock observation with ELT+
HARMONI. The spectrum shows a clear detection of
the He II line from Pop III stars, in a 10-hr exposure.
2 × 10 8
b) 0
1.6 1.8 2.0 2.2 2.4
Wavelength (μm)
b) log(Flux) in electrons
10 2 101 10 0 10 –1 10 –2 10 –3 10 –4 Rest wavelength (Å) at z = 3.0000
4000 4500 5000 5500 6000
0
10 0.10
20
Fื (normalised)
0.05
Pixels
30
40
0.00
50
–0.05 sn_observed
60 SN 1981B max
0 10 20 30 40 50 60 1.6 × 104 1.8 × 104 2.0 × 104 2.2 × 104 2.4 × 104
Pixels Observed wavelength (Å)
Σgas (M pc –2) N He II 1640 (electrons)
c)
101 10 2 10 3 10 2 10 3
1.0 1.0
25 000
G5, z = 6
G5, z = 6 Post – HSIM
FWHM = 80.7 ± 0.4 km s –1 0.8
N (× 10 –5 electrons s –1)
0.5 20 000 Npeak /Ncont. = 15.49 ± .07
Transmission
Spaxel scale: 10 × 10
15 000 0.6
y (kpc)
0.0
10 000 0.4
–0.5
5000 0.2
50 mas
–1.0 0 0.0
–1.0 –0.5 0.0 0.5 1.0 –1.0 –0.5 0.0 0.5 1.0 1.149 1.150 1.151 1.152 1.153 1.154 1.155
x (kpc) λ (μm)
The NGSS is located on top of the IFS top of the cryostat and the NGSS. Both just past the instrument slow shutter,
cryostat and co-rotates with it. It houses the FPRS and NGSS are maintained in a close to where telescope light enters the
the natural guide star sensors for all four dry gas environment at a constant tem- instrument, at a beam height of 6 m
operating modes. As the telescope’s perature of –15 degrees C, reducing above the Nasmyth platform. The first
back focal distance is insufficient to thermal background for improved K-band element in the instrument light path is
relay the telescope light directly into the sensitivity and minimising thermal drifts. the LGS dichroic, which sends light at
upward-looking cryostat, a focal-plane 589 nm from the ELT’s six LGS to the
relay system (FPRS) re-images 2 arcmin- The LGS System (LGSS) and the LGSS. As the LGS asterism is projected
utes of the telescope focal plane to the Calibration Module (CM) are located from the periphery of the ELT primary
10 The Messenger 182 | 2021
mirror (M1), it co-rotates with the tele- non-destructive readout saved in the required exposure time or even the feasi-
scope pupil, and the LGSS needs its own archive. AO telemetry data, useful for bility of the planned observation. It also
de-rotator to compensate. The CM can reconstructing the PSF during the expo- allows the user to develop and test the
insert light from calibration lamps via fold sure, will also be archived. analysis tools required. The HSIM code is
mirrors into the beam path, mimicking publicly available2.
the telescope f-ratio and pupil location. It Science calibrations needed by the data
provides line and continuum sources for reduction pipeline, such as arc lamp HSIM predicts point source sensitivities
all science and technical calibrations. The exposures for wavelength calibration, (5σ, 5 hr, 2 × 2-spaxel extraction aper-
Instrument Static Structure (ISS) provides detector bias and dark frames, flat fields ture) of JAB = 25.6, HAB = 26.8, KAB = 25.9
a robust mechanical structure and and vertical line and pinhole masks, will in LTAO mode, with SCAO performance
access to all instrument systems. be carried out the morning after the of JAB = 26.2, HAB = 27.0, KAB = 26.0 at
observations, as is typical for VLT instru- R ~ 3000. The point source sensitivities
ments. ELT instruments are required to do not convey the full picture, so we have
Operation and calibration be light-tight, so calibrations can happen used HSIM to carry out detailed simula-
in parallel for all instruments. With four tions showcasing a few planned observa-
HARMONI is conceptually simple to oper- observing modes, 4 choices of spaxel tions with HARMONI. These range from
ate, as it provides a “point-and-shoot” scale, and 11 grating settings, the number objects in our own Solar System to the
capability. The user selects one of four of distinct configurations needing calibra- most distant galaxies at z ~ 6–10.
operating modes: noAO, SCAO, HCAO tion exceeds 100. Consequently, only the
or LTAO. In addition, the user must configurations used during the night will Jupiter’s moon Io is the most volcanically
choose a setting that specifies a choice be calibrated the following morning. Sci- active body in the Solar System. Groussin
of spaxel scale, grating and, optionally, ence calibrations and additional monitor- et al. (in preparation) have simulated ELT
other user-selectable items (for example, ing calibrations will be used for “health- observations of Io’s hotspots. They show
SCAO dichroic, or apodiser) and the checks” (to monitor trends in instrument that it is possible to distinguish between
instrument is configured accordingly. performance). Efforts will be made to mini- sulphurous and ultra-mafic composition
Accurate pointing is assured by specify- mise night-time calibrations (telluric or of the ejecta by measuring the ejecta’s
ing offsets of the science field centre flux standards) wherever possible. Meth- temperature (see Figure 3a) from their
from the natural guide star. As a conse- ods that use model-based calibrations NIR spectra, using HARMONI’s SCAO
quence, the default acquisition sequence instead are being actively investigated mode providing near diffraction-limited
does not require an acquisition exposure by a number of ESO working groups. spatial resolution.
with the IFS — once the guide star is
acquired and all control loops are closed, Bounissou et al. (2018) have shown that
the first science exposure can commence Performance HARMONI LTAO can provide direct spec-
straight away. Thanks to the unprece- troscopic classification of a supernova
dented spatial resolution of the ELT, the We have developed a python simulator, in a galaxy at z ~ 3 in a 3-hr observation,
accuracy of information needed for guide HSIM1, to provide prospective users with up to 2 months past maximum light (see
stars (proper motion, colour, etc.) is much the ability to quantitatively assess the effi- Figure 3b), using the Si II feature (at
higher than for the Very Large Telescope cacy of their proposed observing pro- 400 nm in the rest frame). Confirming
(VLT). With the faint guide stars which gramme. HSIM (Zieleniewski et al., 2015) type Ia supernovae spectroscopically for
can be used by HARMONI, catalogues is a “cube-in, cube-out” simulator that a small sub-sample will allow studies of
may not suffice and pre-imaging of the mimics the effects of atmosphere, tele- cosmic expansion rates to be pushed to
field might be needed in some cases. scope, instrument and detector, including substantially higher redshifts.
the strongly wavelength-dependent, non-
Observing templates will have a similar axisymmetric AO PSF. The user can ana- We have used the adaptive mesh refine-
look and feel to those of other VLT NIR lyse the output cube as if it were the out- ment cosmological simulations from the
IFS, and will include a variety of sky- put of the instrument pipeline for a real NEW HORIZON suite (Dubois et al., 2020)
subtraction strategies such as “offset observation, as it incorporates noise from to simulate studies of high-z galaxies with
to blank sky”, “nod-on-IFU” or “stare”, all sources, including shot noise from HARMONI in a spatially resolved manner.
together with small jitters to work around thermal background and night-sky emis- Using cosmological simulations that cre-
bad or hot pixels. Mosaicking will also be sion, detector readout noise and dark ate galaxies at high spatial resolution
supported in the usual way, as will non- current. Detector systematics and the commensurate with HARMONI’s observa-
sidereal tracking in LTAO and noAO impact of sky subtraction can also be tional capabilities (~ 100 pc at z ~ 2–10) is
modes (in SCAO and HCAO mode, the included if desired. Through detailed preferred because the objects have mor-
only non-sidereal observation possible analysis of the output cube, the astrono- phologies and kinematic and dynamical
is when the AO reference “star” is itself mer can derive uncertainties and confi- properties consistent with the observed
non-sidereal). NIR long exposures (typical dence levels for the derived physical ensemble population at high redshifts,
for spectroscopy of faint targets) will use parameters from the observation, rather and have well understood input physics
Sample-Up-The-Ramp (SUTR) readout than just the signal-to-noise ratio per consistent with known laws and cosmo-
to minimise readout noise, with every spaxel (or pixel), thus quantifying the logical evolution (Richardson et al., 2020).
The Messenger 182 | 2021 11
ELT Instrumentation Thatte N. et al., HARMONI
Grisdale et al. (2020) have used NEW from a substantial fraction of the mock Olivier Groussin (Io simulations) and Kearn Grisdale
(Pop III simulations). We are also grateful to James
HORIZON simulations, post-processed galaxies in a 10-hr exposure (Figure 3c).
Carruthers, Neil Campbell, and David Montgomery
using the CLOUDY radiative transfer However, to be certain that the line for CAD views. Miguel Pereira-Santaella is the
code (Ferland et al., 2017) to show indicates the presence of Pop III stars author of HSIM and we thank him for the sens i-
that HARMONI LTAO could detect the would require ancillary observations of tivity computations.
presence of the first stars (Pop III stars) in the H-alpha line from these objects to
galaxies at very high redshifts (z = 3–10). measure the He II to H-alpha ratio, prob- References
The existence of Pop III stars has not ably using the James Webb Space
been observationally confirmed up to Telescope, given the high redshifts Bounissou, S. et al. 2018, MNRAS, 478, 3189
Carlotti, A. et al. 2018, Proc. SPIE, 10702, 107029N
now, although several attempts have involved.
Dubois, Y. et al. 2020, arXiv:2009.10578
been made and some excellent candi- Ferland, G. J. et al. 2017, Revista Mexicana
dates have been identified. Given their de Astronomía y Astrofísica, 53, 385
primordial composition with no heavy Acknowledgements Grisdale, K. et al. 2021, MNRAS, 501, 5517
N’Diaye, M. et al. 2016, Proc. SPIE, 9909, 99096S
elements, Pop III stars are expected to HARMONI work in the UK is supported by the Richardson, M. et al. 2020, MNRAS, 498, 1891
be substantially more massive than their Science and Technology Facilities Council (STFC) Zieleniewski, S. et al. 2015, MNRAS, 453, 3754
metal-rich cousins. Consequently, they at the UK Astronomy Technology Centre (UKATC),
should burn much hotter, and have a Rutherford Appleton Laboratory (RAL), University of
Oxford (grants ST/N002717/1 and ST/S001409/1) Links
much higher ultraviolet flux, capable of and Durham University (grant ST/S001360/1), as part
ionising not only hydrogen but also helium of the UK ELT Programme. In France, the HARMONI 1
HSIM simulator: https://harmoni-elt.physics.ox.ac.
in the surrounding gas (H II region). The Project is supported by the CSAA-CNRS/INSU, uk/Hsim.html
strength of the He II 164 nm line is thus ONERA, A*MIDEX, LABEX LIO, and Université 2
HSIM code: https://github.com/HARMONI-ELT/HSIM
Grenoble Alpes. The IAC and CAB (CSIC-INTA)
a good observational diagnostic for the acknowledge support from the Spanish MCIU/AEI/
presence of Pop III stars. Despite the FEDER UE (grants AYA2105-68217-P, SEV-2015- Notes
large luminosity distance of these very 0548, AYA2017-85170-R, PID2019-107010GB-100,
high-redshift star forming regions, the CSIC-PIE201750E006, and PID2019-105423GA-I00) a
The full list of HARMONI Consortium members can
and from the Comunidad de Madrid (grant 2018-T1/ be found at https://harmoni-elt.physics.ox.ac.uk/
ELT’s huge collecting area, coupled with TIC-11035). consortium.html
the exquisite spatial resolution provided b
Spaxel stands for SPAtial piXEL, to distinguish it
by HARMONI LTAO, would detect the The authors would like to acknowledge contributions from a pixel of the spectrograph detector.
He II feature with good signal-to-noise from Sophie Bounissou (supernova simulations),
ESO/SPECULOOS Team/E. Jehin
If you had a brand new
state-of-the-art tele-
scope facility, what
would you look at first?
Researchers at the
SPECULOOS Southern
Observatory — which
comprises four small tel-
escopes, each with a
1-metre primary mirror
— chose to view the
Lagoon Nebula. This
magnificent picture is
the result, and is one of
the SPECULOOS’ first
ever observations.
12 The Messenger 182 | 2021
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