Florian Lang-Bardl

The 4MOST instrument concept overview

The 4MOST[1] instrument is a concept for a wide-field, fibre-fed high multiplex spectroscopic instrument facility on the ESO VISTA telescope designed to perform a massive (initially >25x106 spectra in 5 years) combined all-sky public survey. The main science drivers are: Gaia follow up of chemo-dynamical structure of the Milky Way, stellar radial velocities, parameters and abundances, chemical tagging; eROSITA follow up of cosmology with x-ray clusters of galaxies, X-ray AGN/galaxy evolution to z~5, Galactic X-ray sources and resolving the Galactic edge; Euclid/LSST/SKA and other survey follow up of Dark Energy, Galaxy evolution and transients. The surveys will be undertaken simultaneously requiring: highly advanced targeting and scheduling software, also comprehensive data reduction and analysis tools to produce high-level data products. The instrument will allow simultaneous observations of ~1600 targets at R~5,000 from 390-900nm and ~800 targets at R<18,000 in three channels between ~395-675nm (channel bandwidth: 45nm blue, 57nm green and 69nm red) over a hexagonal field of view of ~ 4.1 degrees. The initial 5-year 4MOST survey is currently expect to start in 2020. We provide and overview of the 4MOST systems: optomechanical, control, data management and operations concepts; and initial performance estimates.

4MOST-4-metre Multi-Object Spectroscopic Telescope

4MOST is a wide-field, high-multiplex spectroscopic survey facility under development for the VISTA telescope of the European Southern Observatory (ESO). Its main science drivers are in the fields of galactic archeology, high-energy physics, galaxy evolution and cosmology. 4MOST will in particular provide the spectroscopic complements to the large area surveys coming from space missions like Gaia, eROSITA, Euclid, and PLATO and from ground-based facilities like VISTA, VST, DES, LSST and SKA. The 4MOST baseline concept features a 2.5 degree diameter field-of-view with ~2400 fibres in the focal surface that are configured by a fibre positioner based on the tilting spine principle. The fibres feed two types of spectrographs; ~1600 fibres go to two spectrographs with resolution R<5000 (λ~390-930 nm) and ~800 fibres to a spectrograph with R>18,000 (λ~392-437 nm and 515-572 nm and 605-675 nm). Both types of spectrographs are fixed-configuration, three-channel spectrographs. 4MOST will have an unique operations concept in which 5 year public surveys from both the consortium and the ESO community will be combined and observed in parallel during each exposure, resulting in more than 25 million spectra of targets spread over a large fraction of the southern sky. The 4MOST Facility Simulator (4FS) was developed to demonstrate the feasibility of this observing concept. 4MOST has been accepted for implementation by ESO with operations expected to start by the end of 2020. This paper provides a top-level overview of the 4MOST facility, while other papers in these proceedings provide more detailed descriptions of the instrument concept[1], the instrument requirements development[2], the systems engineering implementation[3], the instrument model[4], the fibre positioner concepts[5], the fibre feed[6], and the spectrographs[7].

MICADO: first light imager for the E-ELT

MICADO will equip the E-ELT with a first light capability for diffraction limited imaging at near-infrared wavelengths. The instrument’s observing modes focus on various flavours of imaging, including astrometric, high contrast, and time resolved. There is also a single object spectroscopic mode optimised for wavelength coverage at moderately high resolution. This contribution provides an overview of the key functionality of the instrument, outlining the scientific rationale for its observing modes. The interface between MICADO and the adaptive optics system MAORY that feeds it is summarised. The design of the instrument is discussed, focusing on the optics and mechanisms inside the cryostat, together with a brief overview of the other key sub-systems.MICADO will be the first-light wide-field imager for the European Extremely Large Telescope (E-ELT) and will provide difiraction limited imaging (7mas at 1.2mm) over a ~53 arcsecond field of view. In order to support various consortium activities we have developed a first version of SimCADO: an instrument simulator for MICADO. SimCADO uses the results of the detailed simulation efforts conducted for each of the separate consortium-internal work packages in order to generate a model of the optical path from source to detector readout. SimCADO is thus a tool to provide scientific context to both the science and instrument development teams who are ultimately responsible for the final design and future capabilities of the MICADO instrument. Here we present an overview of the inner workings of SimCADO and outline our plan for its further development.

The 64 Mpixel wide field imager for the Wendelstein 2m telescope: design and calibration

The Wendelstein Observatory of Ludwig Maximilians University of Munich has recently been upgraded with a modern 2m robotic telescope. One Nasmyth port of the telescope has been equipped with a wide-field corrector which preserves the excellent image quality (<0.8” median seeing) of the site (Hopp et al. 2008) over a field of view of 0.7 degrees diameter. The available field is imaged by an optical imager (WWFI, the Wendelstein Wide Field Imager) built around a customized 2×2 mosaic of 4k×4k 15 μm e2v CCDs from Spectral Instruments. This paper provides an overview of the design and the WWFI’s performance. We summarize the system mechanics (including a structural analysis), the electronics (and its electromagnetic interference (EMI) protection) and the control software. We discuss in detail detector system parameters, i.e. gain and readout noise, quantum efficiency as well as charge transfer efficiency (CTE) and persistent charges. First on sky tests yield overall good predictability of system throughput based on lab measurements.

First tests of the compact low scattered-light 2m-Wendelstein Fraunhofer Telescope

The integration of the 2m Fraunhofer telescope started in August 2011 at the Mt. Wendelstein observatory. The logistics of the project are a key problem of the integration as the observatory has no road access. All large or heavy components inlcuding the primary mirror were successfully delivered by helicopter. Meanwhile, they are integrated in the telescope. The special design features of this alt-az telescope are its compactness and the low-ghost wide field optics (0.7 deg. f.o.v. diameter). We will briefly report on tests of the building and of the telescope system before the telescope moved to the mountain. The integration at the observatory and the first astronomical performances tests of the telescopes are discussed, and a brief update on the status of its instruments is presented. We comment on the cleaning and recoating strategy for the primary mirror based on sample tests.

Pressure and temperature stabilization of an existing Echelle spectrograph

The Echelle spectrograph FOCES1 is currently located at the laboratories of Munich University Observatories under pressure and temperature stabilized conditions. It is being used as a test bed for a number of different stability issues related to high precision radial velocity spectroscopy. We utilize FOCES to study spectrograph stability, illumination stability and fiber transport stability. With this work we continue the series of papers that present our efforts to obtain temperature and pressure stabilization in the spectrograph environment. In particular we present first optical measurement results and compare them to simulations previously published. We show the movement of the image on the CCD with changes of pressure and temperature and the stability of the spot positions in the stabilized system using measurements done by a ThAr gas discharge source.

A testbed for simultaneous measurement of fiber near and far-field for the evaluation of fiber scrambling properties

To improve our understanding of fiber scrambling properties a test bed where fiber near-field and far-field can be measured simultaneously is described. A variety of measurements has been conducted with a selection of fibers from different vendors, including state-of-the-art octagonal and hexagonal fibers. After characterization of the test bench with respect to stability and resolution, scrambling measurements have been conducted using LEDs with central wavelengths ranging between 465-635 nm. The dependence on wavelength regarding to photometrical scrambling has been initially demonstrated. Moreover, two mechanical combined fiber cables have been analyzed that were made from octagonal-circular and hexagonal-octagonal fiber sections. In this context an apparatus for focal ratio degradation (FRD) measurements was assembled to compare different shaped fibers and fiber combinations. Finally, all these preliminary investigations will help in choosing a fiber with good radial scrambling performance for the next generation fiber-link of the fiber optic coupled Cassegrain echelle spectrograph FOCES intended to be operated at the 2.0m Fraunhofer Telescope at the Wendelstein Observatory.

Stability of the FOCES spectrograph using an astro-frequency comb as calibrator

We present the results of a series of measurements conducted using the upgraded Fiber Optic Cassegrain Echelle Spectrograph (FOCES)1 intended to be operated at the 2.0 m Fraunhofer Telescope at the Wendelstein Observatory (Germany) in combination with a laser frequency comb as calibrator. Details about the laboratory set-up of the system integrated with FOCES are shown. Different analysis techniques are applied to investigate the calibration precision and the medium-long term stability of the system in term of changes in stellar radial velocity.

New Fraunhofer Telescope Wendelstein: assembly, installation, and current status

Due to the exposed location of the Wendelstein observatory on the steep summit of mount Wendelstein no road exists to transport telescope components and heavy equipment to the observatory in order to install the new 2m Fraunhofer Telescope Wendelstein (FTW) in its new dome. A two step installation concept was therefore followed to mitigate any risks that essential hardware would not work once installed on the mountain. This paper reports on the telescope factory assembly and tests, including on-sky tests, which were performed in early summer 2011 at the factory site to make sure, that the telescope and all essential subsystems are working properly before the telescope would be installed on the mountain. The telescope was disassembled again to be transported to the mountain in summer. Lifting of all structural subsystems and the optics up to the mountain observatory with the help of a heavy lift helicopter will be presented in detail, also looking at specific design drivers, logistic aspects and special tools for installation of the telescope and its mirrors in its new dome. Handling and transport concept for the M1 mirror installation, which also will have to be used when the mirror is disassembled for recoating, are presented. Up to end of 2011 the telescope installation and pre-alignment could be completed including first on-sky tests. The system will undergo a detailed performance test campaign in the first halve of 2012. Current performance results of these commissioning activities will be reported.

A wide field corrector concept including an atmospheric dispersion corrector for the ESO-NTT

An optical design for a wide field corrector (WFC) turning the ESO New Technology Telescope (NTT) into a powerful fiber coupled spectroscopic wide filed, multi object facility is presented. The design utilizes a three square degree (optional 5 square degrees are possible) field of view (FoV) and is designed for a 1.5 arcsec diameter fibre aperture. One of the three lenses of the corrector system is shifted laterally to achieve atmospheric dispersion correction. Image quality properties and a basic tolerancing analysis is shown with this paper.