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\def\teff{$T\rm_{eff }$}
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\title{
T-REX OU4 HIRES: the high resolution spectrograph for the E-ELT
}

   \subtitle{}

\author{
E. Oliva\inst{1} 
  \and
C. Baffa\inst{1} \and
L. Busoni\inst{1} \and % nella lista proposta
L. Carbonaro\inst{1} \and
G. Cresci\inst{1} \and
C. Del Vecchio\inst{1} \and
S. Esposito\inst{1} \and % nella lista proposta
D. Ferruzzi\inst{1} \and
E. Giani\inst{1} \and
M. Iuzzolino\inst{1} \and
F. Massi\inst{1} \and
L. Miglietta\inst{1} \and
E. Pinna\inst{1} \and % nella lista proposta
A. Riccardi\inst{1} \and % nella lista proposta
N. Sanna\inst{1} \and
M. Sozzi\inst{1} \and
A. Tozzi\inst{1} \and
% UNIFI
M. Curti\inst{2} \and
S. Faggi\inst{2} \and
A. Marconi\inst{2} \and
% Bologna
A. Bragaglia\inst{3} \and
P. Montegriffo\inst{3} \and % nella lista proposta
L. Origlia\inst{3} \and
% Catania
P. Bruno\inst{4} \and
M. Munari\inst{4} \and
S. Scuderi\inst{4} \and
% UniCT
F. Leone\inst{5} \and
%  Milano
M. Genoni\inst{6} \and
M. Landoni\inst{6} \and % nella lista proposta
E. Poretti\inst{6} \and % nella lista proposta
M. Riva\inst{6} \and
F. Zerbi\inst{6} \and
% Padova
I. Carleo\inst{7} \and
R. Gratton\inst{7} \and
% Roma
S. Antoniucci\inst{8} \and
%F. D'Alessio\inst{8} \and % nella lista proposta
%T. Giannini\inst{8} \and % nella lista proposta
G. Li Causi\inst{8} \and
B. Nisini\inst{8} \and
F. Vitali\inst{8} \and
% Trieste
R. Cirami\inst{9} \and % nella lista proposta
I. Coretti\inst{9} \and % nella lista proposta
S. Cristiani\inst{9} \and
G. Cupani\inst{9} \and
V. D'Odorico\inst{9} \and
P. Di Marcantonio\inst{9} \and
P. Molaro\inst{9} \and
M. Viel\inst{9} %\and % nella lista proposta
      }

  \offprints{E. Oliva}
 

\institute{
INAF - Osservatorio di Arcetri, largo E. Fermi 5, I-50125 Firenze, Italy
\email{oliva@arcetri.inaf.it}
  \and
Universit\`a di Firenze Dip. Fisica e Astronomia,
Via G. Sansone 1, I-50019 Sesto Fiorentino, Italy
  \and
INAF - Osservatorio di Bologna, via Ranzani 1, I-40127 Bologna, Italy
  \and 
INAF -  Osservatorio di Catania, via S.Sofia 78, I-95123 Catania, Italy
  \and
Universit\`a di Catania Dip. Fisica e Astronomia,
   via S.Sofia 78, I-95123 Catania, Italy
  \and
INAF - Osservatorio di Brera, via Brera 28, I-20121 Milano, Italy
  \and
INAF -  Osservatorio di Padova, Vicolo dell'Osservatorio 5, 
     I-35122 Padova, Italy
  \and
INAF -  Osservatorio di Roma, Via di Frascati 33, 
   I-00040 Monteporzio Catone, Italy
 \and
INAF -  Osservatorio di Trieste, Via G.B. Tiepolo 11, I-34143 Trieste, Italy
 }

\authorrunning{E. Oliva }


\titlerunning{T-REX OU4 HIRES}


\abstract{
The goal of this unit was to consolidate the 
project for the construction of the high resolution spectrometer of the 
E-ELT (HIRES).
The task included the development of scientific cases and tools to 
predict  the instrumental performances. From the technical point of
view it included several R\&D activities in collaboration with highly
specialized Italian companies; it
culminated with the detailed design of a highly modular instrument
based on well established technologies.
From the management point of view it lead to the consolidation of a large
international consortium that spans over 12 countries and includes most of the 
European and ESO-related institutes interested in high resolution 
spectroscopy. This consortium
is led by INAF; its formal creation is awaiting the official call by ESO
for the phase-A study for the HIRES instrument of the E-ELT.

\keywords{Instrumentation: spectrographs -- Techniques: high resolution 
spectroscopy -- Telescopes: Extremely Large Telescopes}
}
\maketitle{}

\section{Introduction}
The Italian astronomical community has always demonstrated great
interest in high-resolution spectroscopy both from the scientific and 
technical points of view. Different groups of INAF astronomers played
crucial roles in the projects for the construction of spectrometers for 
the TNG (SARG, GIANO) and for ESO-VLT (UVES-FLAMES, XSHOOTER, ESPRESSO, 
CRIRES). 
INAF was deeply involved in the early (2007-2010)
phase-A studies for the high resolution spectrographs for E-ELT. 
INAF led the international consortium that presented the 
infrared high-resolution spectrograph (SIMPLE), and was a
major contributor to the consortium that studied CODEX, 
the visual high-resolution spectrometer.
%
Within the re-organization of the E-ELT project, ESO 
published in 2011 a detailed proposal for the construction of the
telescope and instruments.
%\footnote{\footnotesize The document is 
%available on the ESO web-site http://www.eso.org/sci/facilities/eelt/}.
In this document ESO identified two first-light instruments
(ELT-CAM/MAORY and ELT-IFU) and other three instruments 
with equal scientific priority, namely ELT-MIR 
(a middle-infrared camera and spectrometer), ELT-MOS
(a multi-objects spectrograph) and ELT-HIRES (a HR spectrograph 
covering the optical and infrared $\lambda$-ranges).
The ESO road-map originally foresaw a call for proposals for ELT-MOS and
ELT-HIRES in 2013; this date was later on shifted forward in time. 
Given the widespread interest of the Italian scientific community towards
spectroscopy, a dedicated operative unit (OU4) for the study of 
ELT-HIRES was included in the TREX project.
%This paper summarizes the results activities of OU4.


\section{Science cases and requirements}

HIRES is conceived to be a versatile instrument capable of 
pursuing a range of key science cases most of which can only be 
achieved through high spectral resolution with the photon collecting 
area provided by the E-ELT. In the following we give a very concise 
summary of the main science cases and requirements, extracted from the HIRES 
white paper \cite{white_paper}.  
The characterization of exoplanets is 
one of the outstanding key science cases for HIRES. The focus will be on 
characterizing exoplanet atmospheres over a wide range of masses, from 
Neptune-like down to Earth-like including those in the habitable zones.
The ultimate goal is the detection of signatures of life. 
The key requirements for are a spectral resolution R$\sim$10$^5$ (primarily to 
disentangle the exoplanet atmospheric features from the telluric 
absorption lines of our atmosphere) a wide wavelength range 
(0.37-2.5~$\mu$m), high stability of the PSF on the detector during 
planetary transits and high flat-fielding accuracy. 
A polarimetric mode would further enhance the exoplanet diagnostic 
capabilities of HIRES, especially for the detection of bio-signatures. 
HIRES will also provide the unique capability 
of revealing the dynamics, chemistry and physical conditions of the 
inner regions of the accretion disks and protoplanetary disks of young 
stellar objects, hence providing unprecedented constraints on the 
physics of star and planets formation. To achieve these goals
 the instrument’s high spectral resolution should be 
accompanied with spatially resolved information  (IFU mode)
at the diffraction limit of the E-ELT. This science case would 
also benefit from a polarimetric mode for the measurement of
magnetic fields in the accretion disk. 
In the field of stellar abundances HIRES with broad spectral coverage
and R$\sim$10$^5$ will reveal the origin and the formation history of ancient
stars belonging to different Galactic components, by studying 
chemical enrichment pattern of solar-type and cooler dwarf stars out to 
distances of several kpc (i.e. sampling most of the Galactic disk 
and bulge) or sub-giants and red giants in the outer Galactic Halo and 
in neighbouring dwarf galaxies. 
In the context of galaxy formation and cosmology, one of the 
exciting prospects is the detection of elements synthesized by 
the first stars in the early Universe. HIRES will probably be the first 
facility that will detect the fingerprint of PopIII stars by measuring 
the chemical enrichment typical of this population in the Inter-Galactic 
(IGM) and Inter-Stellar Medium (ISM) in the foreground of Quasars, GRBs 
and Super-Luminous Supernovae at high red-shift, probing in this way the 
epoch of re-ionization. 
%These observations will reveal the nature and 
%physical properties of the first stars that populated the Universe and
%to trace the history of the re-ionization process of the Universe.
With some MOS capabilities (i.e. simultaneous spectroscopy of 5-10 objects
at R~$\sim$20,000) HIRES will also be able to 
obtain a three-dimensional map of the cosmic web and of the distribution
of metals in the IGM at high 
red-shift, by probing absorption systems towards multiple lines of sight 
on scales of a few arc-minutes.
The same MOS capabilities 
are also required to investigate the processes driving the evolution of 
massive early type galaxies, during the epochs of their formation and 
assembly (z$\sim$1-3).
HIRES with an IFU sampling the ELT 
diffraction limit will be the only instrument able to measure the 
low mass end of 
super-massive black hole in galactic nuclei, which bears signature of 
primordial black hole seeds. 
%%%
\input{figure1_v02}
%%%
Perhaps most exciting, HIRES will be an 
instrument capable of addressing issues that go beyond the limited field 
of Astronomy, breaking into the domain of "fundamental physics". In 
particular, HIRES will provide the most accurate constraints on a 
possible variation of the fundamental constants of nature, and in 
particular of the fine structure constant $\alpha$ and of the 
proton-to-electron mass ratio $\mu$.
By measuring the red-shift drift-rate 
$dz/dt$ of absorption features in distant QSOs, HIRES will be the only 
instrument capable of obtaining a direct and completely 
model-independent measurement of the Universe’s expansion history.
% (the "Sandage test"). 
This should be regarded as the beginning of a legacy 
experiment lasting several decades. 
%However, in addition to high- 
%spectral resolution, this measurement requires a very 
%accurate absolute wavelength calibration and stability of about 2 cm/s.
%that can be 
%achieved with laser comb technology and high fiber scrambling 
%efficiency.


\section{Instrument design}
\input{figure2_v02}
\input{table1_v02}
Designing a high resolution spectrograph with wide spectral coverage for the 
E-ELT represents a challenge for two main reasons. The immense 
A$\Omega$ of a 40-meters class telescope operated in seeing-limited mode 
requires some 
level of A$\Omega$ splitting in order to contain the design in 
sizes for which the optics can be 
manufactured. In addition, operating the instrument from the blue to the 
K band requires different detector and opto-mechanical technologies,
e.g. a cryogenic environment for the IR optics. A modular fiber-fed 
cross-dispersed echelle spectrograph is considered as a viable baseline 
solution. The overall concept is summarized in Figure~\ref{fig1}. 
The light from 
the telescope is split, via dichroics, into four wavelength channels. Each 
wavelength channel includes several telescope optical interfaces that 
feed, through groups of fibers, a dedicated spectrograph module. Each 
telescope-interface and fiber-bundle corresponds to an observing mode. 
Our study indicates that the instrument can be most conveniently divided
in four spectrograph modules as 
shown in Figure~\ref{fig1}.  
The splitting in wavelengths approximately matches  
the photometric bands, i.e. B, VRI, YJH and K. The shortest wavelength 
is 0.37~$\mu$m but could be extended to the ultraviolet by adding a U
(0.33-0.37~$\mu$m) channel to the B module. 
The split in $\lambda$'s among the modules is influenced, among 
all other parameters by the optical transparency of the different types 
of fibers available on the market. Therefore, the different modules can 
be positioned at different distances from the telescope focal plane. All 
spectrometer modules have a fixed configuration, i.e. no moving parts. 
They include a series of parallel entrance slits, each generated from a 
separate set of fibers that, in turn, determines the observing mode
(see Figure\~ref{fig2}).
Observing modes are selected at the level of the telescope interface. 
The three basic observing modes (HR, MR, HR$^2$-IFU) are shown in 
Figure~\ref{fig2}; their 
parameters are listed in Table~\ref{table1}. A fourth mode, 
namely UHR, can be added in order to provide even higher resolution
i.e. R$\sim$150,000.
With such a modular approach one could also 
increase the number of observing modes by adding other sets of fibers 
and telescope interfaces.
% and
%distribute in time the
%development and delivery of the different spectrographs.

\section{Conclusions}
The study demonstrated that a high-resolution spectrometer (R$\sim$10$^5$) 
for E-ELT covering a wide $\lambda$-range (0.37 to 2.5$\mu$m) 
can reach unprecedented scientific goals 
and can be built with currently available technology.
The widespread interest in this project led to the creation of a
large international collaboration that started as "HIRES initiative"
(\cite{zerbi2014}). 
%and that is waiting for the ESO call for phase-A
%study to formally set-up the HIRES-consortium.

The modularity 
of the HIRES concept can guarantee the best use of time and resources. 
The project can be developed with different time-lines 
for the various sub-systems, depending on the available funds. 
It is 
reasonable to consider an early delivery of one or two spectrograph 
modules, with a limited front end. The other spectral modules and full 
interface capabilities (polarimetry, MR and HR$^2$-IFU modes) can be added 
later on.  
Being a fiber-fed instrument designed for seeing limited 
observations, the main performances of HIRES will not depend on external
adaptive optics nor variations of pupil illumination (e.g. 
missing segments from primary mirror). 



 
%\begin{acknowledgements}
%\end{acknowledgements}

\bibliographystyle{aa}
\begin{thebibliography}{}

%\bibitem[Iuzzolino et al. 2014]{iuzzolino2014}
%Iuzzolino, M. et al., 2014, SPIE 9147E, 66I

\bibitem[Maiolino et. al. (2013)]{white_paper}  
Maiolino, R. et al., 2013, arXiv:1310.3163

%\bibitem[Sanna et al. 2014]{sanna2014}
%Sanna, N. et al., 2014, SPIE 9147E, 90S

%\bibitem[Udry et al. 2014]{udry2014}
%Udry, S. et al., 2014, arXiv:1412.1048

\bibitem[Zerbi et al. 2014]{zerbi2014}
Zerbi, F. el al., 2014, SPIE 9147E, 23Z


\end{thebibliography}


\end{document}

