Think big multi-object spectroscopy with extremely large telescopes by xiangpeng



Think big: multi-object
spectroscopy with extremely
large telescopes
Andreas Kelz, Martin M. Roth, Joss Bland-Hawthorn,
Roland Bacon, Harald Nicklas, and Roger Haynes

Deployable fiber bundles and advanced photonics technologies are the
backbone of an innovative, highly modular spectrograph concept.

Designing and building the next generation of extremely
large telescopes (ELTs) is arguably the greatest challenge ever
undertaken by astronomers. ELTs will address the major sci-
ence issues of the next two decades, enabled by huge gains
in sensitivity resulting from collecting areas that are more
than 25 times larger than those of the largest telescopes to-
day. Using current technologies, the size, complexity, and cost
of instrumentation increases with the square of a telescope’s
diameter.1 Building scaled-up versions of the current genera-         Figure 1. The 42m (diameter) European Extremely Large Telescope,
tion of instruments seems beyond reasonable limits of feasibil-       planned for completion in 2018 ( c European Southern Observatory).
ity for the planned 42m (diameter) European ELT (E-ELT: see
Figure 1). New and innovative approaches in instrument lay-
                                                                      an optical integral-field spectrograph for ESO’s 8m (diameter)
out, system engineering, and manufacturing strategies are re-
                                                                      Very Large Telescope (VLT). The instrument is scheduled for
                                                                      commissioning in 2012.
   In the European astronomical community, the highest priority
                                                                         Encouraged by the superb image quality and high throughput
for ground-based optical and near-IR instrumentation has been
                                                                      of the spectrograph optics, we propose a scalable configuration
identified as high-multiplex, multi-object spectroscopy (MOS).2
                                                                      of such modules that can be manufactured in a small industrial
For the E-ELT, the European Southern Observatory (ESO) has
                                                                      series and modified for use with fiber-optical mini-integral-field
awarded support for several concept studies,3 some of which
                                                                      units (IFUs) instead of image slicers. The fiber-based IFUs can be
address MOS approaches. In addition, as members of an in-
                                                                      deployed over the telescope’s full field of view and feature in-
ternational consortium, we are investigating an alternative that
                                                                      novative photonics devices, so-called hexabundles.6 These fused
offers various advantages, including significant science gains be-
                                                                      fiber bundles (see Figure 3) offer large filling factors compared to
cause of a high multiplex factor and flexible deployment, low
                                                                      classical bundles and a much simpler and more compact pack-
cost associated with small sizes of individual units, easy scaling
                                                                      age than microlens-array-fed fiber approaches. The system de-
because of a modular approach, and minimum risk using proven
                                                                      sign profits from the Anglo-Australian Observatory’s experience
                                                                      in developing robotic fiber positioners, such as the successful
   Our proposed MOS instrument concept, ERASMUS-F,4 builds
                                                                      OzPoz facility at the VLT.
on the consortium’s combined expertise. Technologically, it is
based on optical-fiber systems and the spectrograph subsystems
of the Multi-Unit Spectroscopic Explorer (MUSE: see Figure 2),5                                                 Continued on next page
                                                                                              10.1117/2.1201004.002901 Page 2/3

Figure 2. The first of 24 Multi-Unit Spectroscopic Explorer spec-
trographs during acceptance testing ( c Centre de Recherche As-
tronomique de Lyon).
                                                                   Figure 3. Fused hexabundle consisting of 61 fibers ( c University of
   An appealing feature of ERASMUS-F is the idea to deploy
a proof-of-concept E-ELT pathfinder instrument at the VLT,
                                                                   The participating partners in the ERASMUS-F study include the
which—at the same time—is fully justified as a highly compet-
                                                                   Astrophysikalisches Institut Potsdam (Germany), the Centre de
itive common-user facility. The primary goal is to extend the
                                                                   Recherche Astronomique de Lyon (France), the University of Syd-
science remit from integrated to resolved properties of a large
                                                                                                  ¨               o
                                                                   ney (Australia), the Institut fur Astrophysik G¨ ttingen (Germany),
sample of 100,000 galaxies. We presented a summary of the
                                                                   the Anglo-Australian Observatory (Australia), and the innoFSPEC-
science case for the proposed MOS instrument, dubbed ‘FIRE-
                                                                   Potsdam innovation center (Germany). The German partners
BALL,’ to the ESO community in 2009.7
                                                                   acknowledge funding from BMBF (Federal Ministry of Education and
   On behalf of the German Verbundforschung (‘collaborative re-
                                                                   Research) Verbundforschung.
search’), the participating institutes in Potsdam and Gottingen
have taken the lead, including the optomechanical design of the
pathfinder instrument and the manufacturing of a laboratory         Author Information
demonstrator. The Centre de Recherche Astronomique de Lyon
designed and tested8 the MUSE spectrograph module, whose           Andreas Kelz, and Martin M. Roth
overall performance and excellent image quality were recently      Astrophysikalisches Institut Potsdam (AIP)
validated.9 The hexabundles were developed and tested at the       Potsdam, Germany
University of Sydney (Australia) and will soon demonstrate
their scientific feasibility at the Anglo-Australian Telescope.     Andreas Kelz heads the 3D spectroscopy program. He works on
   In addition, our concept using deployable fiber IFUs and         the development and use of the IFU instrumentation projects
replicable spectrographs allows combining proven technolo-         MUSE (for ESO’s VLT), the Visible Integral-field Replicable
gies with novel developments in astrophotonics10 into a highly     Unit Spectrograph, VIRUS (for McDonald Observatory, Texas),
modular instrument layout that can be scaled from current tele-    and the Potsdam Multi-Aperture Spectrophotometer, PMAS (for
scopes to the new generation of ELTs with minimum technologi-      Calar Alto Observatory, Spain).
cal and financial risks. By 2011, we will present our ERASMUS-F
study, which addresses the priority identified to develop a high-   Martin Roth is director of the Innovative Fiber-Spectroscopy and
multiplex MOS for the E-ELT. In parallel, new photonics devices,   Sensing (innoFSPEC) center at AIP. He is the principal investiga-
such as fiber-Bragg and arrayed-waveguide gratings, are sub-        tor of both PMAS and the German ERASMUS-F study, and local
jects of research and development11 for possible implementation    MUSE project manager and science team member.

                                                                                                              Continued on next page
                                                                                                     10.1117/2.1201004.002901 Page 3/3

Joss Bland-Hawthorn                                               References
Institute of Astronomy                                            1. J. R. Allington-Smith, Strategies for spectroscopy on Extremely Large Telescopes. I.
                                                                  Image slicing, Mon. Not. R. Astron. Soc. 376, p. 1099, 2007.
The University of Sydney                                          2. ASTRONET infrastructure roadmap: a strategic
Sydney, Australia                                                 plan for European astronomy. Accessed 19 March 2010.
                                                                  3. index.html Euro-
                                                                  pean Southern Observatory: European Extremely Large Telescope instrumentation.
Joss Bland-Hawthorn holds a Federation Fellow Professorship.      Accessed 19 March 2010.
He was previously head of instrument science at the Anglo-        4. A. Kelz, M. Martin, M. M. Roth, H. Nicklas, R. Bacon, J. Bland-Hawthorn,
                                                                  J. C. Olaya, A. Fleischmann, and J. Kosmalski, ERASMUS-F: pathfinder for E-ELT
Australian Observatory. He is interested in near- and far-field    3D instrumentation, Proc. SPIE 7739. In press.
cosmology and astrophotonics.                                     5. R. Bacon et al., New science opportunities offered by MUSE, in A. Moorwood ed.,
                                                                  Science with the VLT in the ELT era, p. 331, 2009. Astrophys. Space Sci. Proc.
                                                                  6. J. Bland-Hawthorn et al., Hexabundles: imaging fibre arrays for low-light astronomical
Roland Bacon                                                      applications, Proc. SPIE 7735. In press.
Observatoire de Lyon
                                                                  BlandHawthorn.pdf The FIREBALL project: 3D spectroscopic survey of 10,000
Centre de Recherche Astronomique de Lyon                          galaxies at z 0:2. Accessed 19 March 2010.
Lyon, France                                                      8. F. Laurent et al., MUSE integral field unit: test results on the first out of 24, Proc.
                                                                  SPIE 7739. In press.
                                                                  9. R. Bacon, L. Pasquini, and H. Boffin.
Roland Bacon is the principal investigator of the MUSE and        announcements/ann1012/index.html ESO announcement ann1012. Accessed 19
                                                                  March 2010.
Spectroscopic Areal Unit for Research on Optical Nebulae          10. J. Bland Hawthorn and P. Kern, Astrophotonics: a new era for astronomical instru-
(SAURON) instrument projects. He is interested in galaxy dy-      ments, Opt. Express 17 (3), p. 1880, 2009.
                                                                  11. M. M. Roth, H.-G. Loehmannsroeben, A. Kelz, and M. Kumke, innoFSPEC:
namics and evolution.
                                                                  fiber optical spectroscopy and sensing, Proc. SPIE 7018, p. 70184X, 2008.
Harald Nicklas
Institute for Astrophysics Gottingen (IAG)
Georg August University
Gottingen, Germany

Harald Nicklas is the IAG manager involved in the optome-
chanical design and integration of ESO’s focal reducer and low-
dispersion spectrograph (FORS), OmegaCAM, and MUSE.

Roger Haynes
MultiChannel Spectroscopy
Potsdam, Germany

Roger Haynes moved from head of instrumentation and instru-
ment science at the Anglo-Australian Observatory (Australia) to
become head of the multichannel-spectroscopy group. He is an
expert on optical fibers and fiber-based instrumentation.

                                                                                                       c 2010 SPIE

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